12240d2b3f7b9f5835868c83ce78d125d1b65212bChris Lattner//===- TailRecursionElimination.cpp - Eliminate Tail Calls ----------------===// 2fd93908ae8b9684fe71c239e3c6cfe13ff6a2663Misha Brukman// 3b576c94c15af9a440f69d9d03c2afead7971118cJohn Criswell// The LLVM Compiler Infrastructure 4b576c94c15af9a440f69d9d03c2afead7971118cJohn Criswell// 54ee451de366474b9c228b4e5fa573795a715216dChris Lattner// This file is distributed under the University of Illinois Open Source 64ee451de366474b9c228b4e5fa573795a715216dChris Lattner// License. See LICENSE.TXT for details. 7fd93908ae8b9684fe71c239e3c6cfe13ff6a2663Misha Brukman// 8b576c94c15af9a440f69d9d03c2afead7971118cJohn Criswell//===----------------------------------------------------------------------===// 92240d2b3f7b9f5835868c83ce78d125d1b65212bChris Lattner// 107152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner// This file transforms calls of the current function (self recursion) followed 117152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner// by a return instruction with a branch to the entry of the function, creating 127152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner// a loop. This pass also implements the following extensions to the basic 137152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner// algorithm: 142240d2b3f7b9f5835868c83ce78d125d1b65212bChris Lattner// 157152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner// 1. Trivial instructions between the call and return do not prevent the 167152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner// transformation from taking place, though currently the analysis cannot 177152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner// support moving any really useful instructions (only dead ones). 18543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner// 2. This pass transforms functions that are prevented from being tail 1924080a98786cf393740cd035e27dd16c12827892Duncan Sands// recursive by an associative and commutative expression to use an 2024080a98786cf393740cd035e27dd16c12827892Duncan Sands// accumulator variable, thus compiling the typical naive factorial or 2124080a98786cf393740cd035e27dd16c12827892Duncan Sands// 'fib' implementation into efficient code. 22d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner// 3. TRE is performed if the function returns void, if the return 23d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner// returns the result returned by the call, or if the function returns a 24d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner// run-time constant on all exits from the function. It is possible, though 25d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner// unlikely, that the return returns something else (like constant 0), and 26d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner// can still be TRE'd. It can be TRE'd if ALL OTHER return instructions in 27d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner// the function return the exact same value. 280cade261322242132905914f613d25d16e1a9ff6Nick Lewycky// 4. If it can prove that callees do not access their caller stack frame, 297f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattner// they are marked as eligible for tail call elimination (by the code 307f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattner// generator). 312240d2b3f7b9f5835868c83ce78d125d1b65212bChris Lattner// 327152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner// There are several improvements that could be made: 337152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner// 347152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner// 1. If the function has any alloca instructions, these instructions will be 357152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner// moved out of the entry block of the function, causing them to be 367152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner// evaluated each time through the tail recursion. Safely keeping allocas 377152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner// in the entry block requires analysis to proves that the tail-called 387152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner// function does not read or write the stack object. 397a2bdde0a0eebcd2125055e0eacaca040f0b766cChris Lattner// 2. Tail recursion is only performed if the call immediately precedes the 407152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner// return instruction. It's possible that there could be a jump between 417152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner// the call and the return. 42d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner// 3. There can be intervening operations between the call and the return that 437152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner// prevent the TRE from occurring. For example, there could be GEP's and 447152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner// stores to memory that will not be read or written by the call. This 457152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner// requires some substantial analysis (such as with DSA) to prove safe to 467152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner// move ahead of the call, but doing so could allow many more TREs to be 477152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner// performed, for example in TreeAdd/TreeAlloc from the treeadd benchmark. 487f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattner// 4. The algorithm we use to detect if callees access their caller stack 497f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattner// frames is very primitive. 502240d2b3f7b9f5835868c83ce78d125d1b65212bChris Lattner// 512240d2b3f7b9f5835868c83ce78d125d1b65212bChris Lattner//===----------------------------------------------------------------------===// 522240d2b3f7b9f5835868c83ce78d125d1b65212bChris Lattner 530e5f499638c8d277b9dc4a4385712177c53b5681Chris Lattner#define DEBUG_TYPE "tailcallelim" 543fc6ef1bb96d9a3194cef667a2d3cbc94e3fb189Chris Lattner#include "llvm/Transforms/Scalar.h" 55c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng#include "llvm/Transforms/Utils/BasicBlockUtils.h" 566a35b40250735a50efe66c88414cdd3b79185019Chris Lattner#include "llvm/Transforms/Utils/Local.h" 57ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner#include "llvm/Constants.h" 582240d2b3f7b9f5835868c83ce78d125d1b65212bChris Lattner#include "llvm/DerivedTypes.h" 592240d2b3f7b9f5835868c83ce78d125d1b65212bChris Lattner#include "llvm/Function.h" 602240d2b3f7b9f5835868c83ce78d125d1b65212bChris Lattner#include "llvm/Instructions.h" 61c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng#include "llvm/IntrinsicInst.h" 620e00c6c561181be7e9cc75ad2fee9cd4cbbfca1eRafael Espindola#include "llvm/Module.h" 632240d2b3f7b9f5835868c83ce78d125d1b65212bChris Lattner#include "llvm/Pass.h" 640cade261322242132905914f613d25d16e1a9ff6Nick Lewycky#include "llvm/Analysis/CaptureTracking.h" 65ea25b48af33be42e19236d8eac26bd42b45bcc1bDan Gohman#include "llvm/Analysis/InlineCost.h" 66cdbd99262286e96729007ac535cd430ecb3d38acDuncan Sands#include "llvm/Analysis/InstructionSimplify.h" 67dd9344f3face8f1978a7f9f393c31b628144d1f6Dan Gohman#include "llvm/Analysis/Loads.h" 68ea25b48af33be42e19236d8eac26bd42b45bcc1bDan Gohman#include "llvm/Support/CallSite.h" 69543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner#include "llvm/Support/CFG.h" 70c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng#include "llvm/Support/Debug.h" 71337c0811381a48b75aec204d96090779fec6606eFrancois Pichet#include "llvm/Support/raw_ostream.h" 72551ccae044b0ff658fe629dd67edd5ffe75d10e8Reid Spencer#include "llvm/ADT/Statistic.h" 73c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng#include "llvm/ADT/STLExtras.h" 74f8485c643412dbff46fe87ea2867445169a5c28eChris Lattnerusing namespace llvm; 75d0fde30ce850b78371fd1386338350591f9ff494Brian Gaeke 760e5f499638c8d277b9dc4a4385712177c53b5681Chris LattnerSTATISTIC(NumEliminated, "Number of tail calls removed"); 7760f5ad46c2147af79035a43e5745e46376124780Evan ChengSTATISTIC(NumRetDuped, "Number of return duplicated"); 780e5f499638c8d277b9dc4a4385712177c53b5681Chris LattnerSTATISTIC(NumAccumAdded, "Number of accumulators introduced"); 792240d2b3f7b9f5835868c83ce78d125d1b65212bChris Lattner 800e5f499638c8d277b9dc4a4385712177c53b5681Chris Lattnernamespace { 813e8b6631e67e01e4960a7ba4668a50c596607473Chris Lattner struct TailCallElim : public FunctionPass { 82ecd94c804a563f2a86572dcf1d2e81f397e19daaNick Lewycky static char ID; // Pass identification, replacement for typeid 83081c34b725980f995be9080eaec24cd3dfaaf065Owen Anderson TailCallElim() : FunctionPass(ID) { 84081c34b725980f995be9080eaec24cd3dfaaf065Owen Anderson initializeTailCallElimPass(*PassRegistry::getPassRegistry()); 85081c34b725980f995be9080eaec24cd3dfaaf065Owen Anderson } 86794fd75c67a2cdc128d67342c6d88a504d186896Devang Patel 872240d2b3f7b9f5835868c83ce78d125d1b65212bChris Lattner virtual bool runOnFunction(Function &F); 887152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner 897152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner private: 90c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng CallInst *FindTRECandidate(Instruction *I, 91c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng bool CannotTailCallElimCallsMarkedTail); 92c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng bool EliminateRecursiveTailCall(CallInst *CI, ReturnInst *Ret, 93c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng BasicBlock *&OldEntry, 94c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng bool &TailCallsAreMarkedTail, 95c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng SmallVector<PHINode*, 8> &ArgumentPHIs, 96c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng bool CannotTailCallElimCallsMarkedTail); 97c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng bool FoldReturnAndProcessPred(BasicBlock *BB, 98c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng ReturnInst *Ret, BasicBlock *&OldEntry, 99c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng bool &TailCallsAreMarkedTail, 100c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng SmallVector<PHINode*, 8> &ArgumentPHIs, 101c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng bool CannotTailCallElimCallsMarkedTail); 1027152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner bool ProcessReturningBlock(ReturnInst *RI, BasicBlock *&OldEntry, 103ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner bool &TailCallsAreMarkedTail, 1040cade261322242132905914f613d25d16e1a9ff6Nick Lewycky SmallVector<PHINode*, 8> &ArgumentPHIs, 105ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner bool CannotTailCallElimCallsMarkedTail); 1067152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner bool CanMoveAboveCall(Instruction *I, CallInst *CI); 107543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner Value *CanTransformAccumulatorRecursion(Instruction *I, CallInst *CI); 1082240d2b3f7b9f5835868c83ce78d125d1b65212bChris Lattner }; 1092240d2b3f7b9f5835868c83ce78d125d1b65212bChris Lattner} 1102240d2b3f7b9f5835868c83ce78d125d1b65212bChris Lattner 111844731a7f1909f55935e3514c9e713a62d67662eDan Gohmanchar TailCallElim::ID = 0; 112d13db2c59cc94162d6cf0a04187d408bfef6d4a7Owen AndersonINITIALIZE_PASS(TailCallElim, "tailcallelim", 113ce665bd2e2b581ab0858d1afe359192bac96b868Owen Anderson "Tail Call Elimination", false, false) 114844731a7f1909f55935e3514c9e713a62d67662eDan Gohman 115d0fde30ce850b78371fd1386338350591f9ff494Brian Gaeke// Public interface to the TailCallElimination pass 116f8485c643412dbff46fe87ea2867445169a5c28eChris LattnerFunctionPass *llvm::createTailCallEliminationPass() { 117f8485c643412dbff46fe87ea2867445169a5c28eChris Lattner return new TailCallElim(); 118f8485c643412dbff46fe87ea2867445169a5c28eChris Lattner} 1193fc6ef1bb96d9a3194cef667a2d3cbc94e3fb189Chris Lattner 120cb19438f63019eb557c1fbaeae8a6de78b03c584Nick Lewycky/// AllocaMightEscapeToCalls - Return true if this alloca may be accessed by 121cb19438f63019eb557c1fbaeae8a6de78b03c584Nick Lewycky/// callees of this function. We only do very simple analysis right now, this 122cb19438f63019eb557c1fbaeae8a6de78b03c584Nick Lewycky/// could be expanded in the future to use mod/ref information for particular 123cb19438f63019eb557c1fbaeae8a6de78b03c584Nick Lewycky/// call sites if desired. 124cb19438f63019eb557c1fbaeae8a6de78b03c584Nick Lewyckystatic bool AllocaMightEscapeToCalls(AllocaInst *AI) { 125cb19438f63019eb557c1fbaeae8a6de78b03c584Nick Lewycky // FIXME: do simple 'address taken' analysis. 126cb19438f63019eb557c1fbaeae8a6de78b03c584Nick Lewycky return true; 127cb19438f63019eb557c1fbaeae8a6de78b03c584Nick Lewycky} 128cb19438f63019eb557c1fbaeae8a6de78b03c584Nick Lewycky 1290cade261322242132905914f613d25d16e1a9ff6Nick Lewycky/// CheckForEscapingAllocas - Scan the specified basic block for alloca 1307f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattner/// instructions. If it contains any that might be accessed by calls, return 1317f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattner/// true. 132ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattnerstatic bool CheckForEscapingAllocas(BasicBlock *BB, 133ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner bool &CannotTCETailMarkedCall) { 134ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner bool RetVal = false; 1357f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattner for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) 136ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner if (AllocaInst *AI = dyn_cast<AllocaInst>(I)) { 137cb19438f63019eb557c1fbaeae8a6de78b03c584Nick Lewycky RetVal |= AllocaMightEscapeToCalls(AI); 138ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner 139ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner // If this alloca is in the body of the function, or if it is a variable 140ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner // sized allocation, we cannot tail call eliminate calls marked 'tail' 141ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner // with this mechanism. 142ecb7a77885b174cf4d001a9b48533b3979e7810dDan Gohman if (BB != &BB->getParent()->getEntryBlock() || 143ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner !isa<ConstantInt>(AI->getArraySize())) 144ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner CannotTCETailMarkedCall = true; 145ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner } 146ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner return RetVal; 1477f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattner} 1487f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattner 1492240d2b3f7b9f5835868c83ce78d125d1b65212bChris Lattnerbool TailCallElim::runOnFunction(Function &F) { 1502240d2b3f7b9f5835868c83ce78d125d1b65212bChris Lattner // If this function is a varargs function, we won't be able to PHI the args 1512240d2b3f7b9f5835868c83ce78d125d1b65212bChris Lattner // right, so don't even try to convert it... 1522240d2b3f7b9f5835868c83ce78d125d1b65212bChris Lattner if (F.getFunctionType()->isVarArg()) return false; 1532240d2b3f7b9f5835868c83ce78d125d1b65212bChris Lattner 1542240d2b3f7b9f5835868c83ce78d125d1b65212bChris Lattner BasicBlock *OldEntry = 0; 155ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner bool TailCallsAreMarkedTail = false; 1560cade261322242132905914f613d25d16e1a9ff6Nick Lewycky SmallVector<PHINode*, 8> ArgumentPHIs; 1572240d2b3f7b9f5835868c83ce78d125d1b65212bChris Lattner bool MadeChange = false; 1587f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattner bool FunctionContainsEscapingAllocas = false; 1597f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattner 160ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner // CannotTCETailMarkedCall - If true, we cannot perform TCE on tail calls 161ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner // marked with the 'tail' attribute, because doing so would cause the stack 162ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner // size to increase (real TCE would deallocate variable sized allocas, TCE 163ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner // doesn't). 164ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner bool CannotTCETailMarkedCall = false; 165ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner 1667f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattner // Loop over the function, looking for any returning blocks, and keeping track 1677f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattner // of whether this function has any non-trivially used allocas. 1687f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattner for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) { 169ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner if (FunctionContainsEscapingAllocas && CannotTCETailMarkedCall) 170ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner break; 17100b16889ab461b7ecef1c91ade101186b7f1fce2Jeff Cohen 1724c0e4cdc40bbf94766242294fe386f4eb2d32d2eChris Lattner FunctionContainsEscapingAllocas |= 173ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner CheckForEscapingAllocas(BB, CannotTCETailMarkedCall); 1747f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattner } 17532b1e87f111d79f3f5b0e86c8f138c02bef8aa18Chris Lattner 17632b1e87f111d79f3f5b0e86c8f138c02bef8aa18Chris Lattner /// FIXME: The code generator produces really bad code when an 'escaping 17732b1e87f111d79f3f5b0e86c8f138c02bef8aa18Chris Lattner /// alloca' is changed from being a static alloca to being a dynamic alloca. 17832b1e87f111d79f3f5b0e86c8f138c02bef8aa18Chris Lattner /// Until this is resolved, disable this transformation if that would ever 17932b1e87f111d79f3f5b0e86c8f138c02bef8aa18Chris Lattner /// happen. This bug is PR962. 18032b1e87f111d79f3f5b0e86c8f138c02bef8aa18Chris Lattner if (FunctionContainsEscapingAllocas) 18132b1e87f111d79f3f5b0e86c8f138c02bef8aa18Chris Lattner return false; 182fd93908ae8b9684fe71c239e3c6cfe13ff6a2663Misha Brukman 183ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner // Second pass, change any tail calls to loops. 184c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) { 185c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng if (ReturnInst *Ret = dyn_cast<ReturnInst>(BB->getTerminator())) { 186c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng bool Change = ProcessReturningBlock(Ret, OldEntry, TailCallsAreMarkedTail, 187ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner ArgumentPHIs,CannotTCETailMarkedCall); 188c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng if (!Change && BB->getFirstNonPHIOrDbg() == Ret) 189c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng Change = FoldReturnAndProcessPred(BB, Ret, OldEntry, 190c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng TailCallsAreMarkedTail, ArgumentPHIs, 191c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng CannotTCETailMarkedCall); 192c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng MadeChange |= Change; 193c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng } 194c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng } 195ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner 196cf2f89251d45bc9783917874adb9029f71d50068Chris Lattner // If we eliminated any tail recursions, it's possible that we inserted some 197cf2f89251d45bc9783917874adb9029f71d50068Chris Lattner // silly PHI nodes which just merge an initial value (the incoming operand) 198cf2f89251d45bc9783917874adb9029f71d50068Chris Lattner // with themselves. Check to see if we did and clean up our mess if so. This 199cf2f89251d45bc9783917874adb9029f71d50068Chris Lattner // occurs when a function passes an argument straight through to its tail 200cf2f89251d45bc9783917874adb9029f71d50068Chris Lattner // call. 201cf2f89251d45bc9783917874adb9029f71d50068Chris Lattner if (!ArgumentPHIs.empty()) { 202cf2f89251d45bc9783917874adb9029f71d50068Chris Lattner for (unsigned i = 0, e = ArgumentPHIs.size(); i != e; ++i) { 203cf2f89251d45bc9783917874adb9029f71d50068Chris Lattner PHINode *PN = ArgumentPHIs[i]; 204cf2f89251d45bc9783917874adb9029f71d50068Chris Lattner 205cf2f89251d45bc9783917874adb9029f71d50068Chris Lattner // If the PHI Node is a dynamic constant, replace it with the value it is. 206cdbd99262286e96729007ac535cd430ecb3d38acDuncan Sands if (Value *PNV = SimplifyInstruction(PN)) { 207ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner PN->replaceAllUsesWith(PNV); 208ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner PN->eraseFromParent(); 209cf2f89251d45bc9783917874adb9029f71d50068Chris Lattner } 210cf2f89251d45bc9783917874adb9029f71d50068Chris Lattner } 211cf2f89251d45bc9783917874adb9029f71d50068Chris Lattner } 212cf2f89251d45bc9783917874adb9029f71d50068Chris Lattner 2130e00c6c561181be7e9cc75ad2fee9cd4cbbfca1eRafael Espindola // Finally, if this function contains no non-escaping allocas, or calls 2140e00c6c561181be7e9cc75ad2fee9cd4cbbfca1eRafael Espindola // setjmp, mark all calls in the function as eligible for tail calls 2150e00c6c561181be7e9cc75ad2fee9cd4cbbfca1eRafael Espindola //(there is no stack memory for them to access). 2160e00c6c561181be7e9cc75ad2fee9cd4cbbfca1eRafael Espindola if (!FunctionContainsEscapingAllocas && !F.callsFunctionThatReturnsTwice()) 2177f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattner for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) 2187f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattner for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) 219febc81680c80a53f15f85b1812cba07fc179b9fdEvan Cheng if (CallInst *CI = dyn_cast<CallInst>(I)) { 220febc81680c80a53f15f85b1812cba07fc179b9fdEvan Cheng CI->setTailCall(); 221febc81680c80a53f15f85b1812cba07fc179b9fdEvan Cheng MadeChange = true; 222febc81680c80a53f15f85b1812cba07fc179b9fdEvan Cheng } 2237f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattner 2242240d2b3f7b9f5835868c83ce78d125d1b65212bChris Lattner return MadeChange; 2252240d2b3f7b9f5835868c83ce78d125d1b65212bChris Lattner} 2267152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner 2277152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner 228543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner/// CanMoveAboveCall - Return true if it is safe to move the specified 229543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner/// instruction from after the call to before the call, assuming that all 230543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner/// instructions between the call and this instruction are movable. 231543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner/// 2327152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattnerbool TailCallElim::CanMoveAboveCall(Instruction *I, CallInst *CI) { 2337152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner // FIXME: We can move load/store/call/free instructions above the call if the 2347152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner // call does not mod/ref the memory location being processed. 2356a35b40250735a50efe66c88414cdd3b79185019Chris Lattner if (I->mayHaveSideEffects()) // This also handles volatile loads. 2367152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner return false; 2376a35b40250735a50efe66c88414cdd3b79185019Chris Lattner 2380cade261322242132905914f613d25d16e1a9ff6Nick Lewycky if (LoadInst *L = dyn_cast<LoadInst>(I)) { 2396a35b40250735a50efe66c88414cdd3b79185019Chris Lattner // Loads may always be moved above calls without side effects. 2406a35b40250735a50efe66c88414cdd3b79185019Chris Lattner if (CI->mayHaveSideEffects()) { 2416a35b40250735a50efe66c88414cdd3b79185019Chris Lattner // Non-volatile loads may be moved above a call with side effects if it 2426a35b40250735a50efe66c88414cdd3b79185019Chris Lattner // does not write to memory and the load provably won't trap. 2436a35b40250735a50efe66c88414cdd3b79185019Chris Lattner // FIXME: Writes to memory only matter if they may alias the pointer 2446a35b40250735a50efe66c88414cdd3b79185019Chris Lattner // being loaded from. 2456a35b40250735a50efe66c88414cdd3b79185019Chris Lattner if (CI->mayWriteToMemory() || 24649db68fba01722ca032dc5170f8248a9d25f0199Bob Wilson !isSafeToLoadUnconditionally(L->getPointerOperand(), L, 24749db68fba01722ca032dc5170f8248a9d25f0199Bob Wilson L->getAlignment())) 2486a35b40250735a50efe66c88414cdd3b79185019Chris Lattner return false; 2496a35b40250735a50efe66c88414cdd3b79185019Chris Lattner } 2506a35b40250735a50efe66c88414cdd3b79185019Chris Lattner } 2517152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner 2527152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner // Otherwise, if this is a side-effect free instruction, check to make sure 2537152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner // that it does not use the return value of the call. If it doesn't use the 2547152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner // return value of the call, it must only use things that are defined before 2557152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner // the call, or movable instructions between the call and the instruction 2567152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner // itself. 2577152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) 2587152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner if (I->getOperand(i) == CI) 2597152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner return false; 2607152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner return true; 2617152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner} 2627152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner 263d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner// isDynamicConstant - Return true if the specified value is the same when the 264d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner// return would exit as it was when the initial iteration of the recursive 265d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner// function was executed. 266d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner// 267d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner// We currently handle static constants and arguments that are not modified as 268d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner// part of the recursion. 269d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner// 270f80fcd00b3590626a6110fe5fbe9b5fd2a8be1aeNick Lewyckystatic bool isDynamicConstant(Value *V, CallInst *CI, ReturnInst *RI) { 271d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner if (isa<Constant>(V)) return true; // Static constants are always dyn consts 272d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner 273d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner // Check to see if this is an immutable argument, if so, the value 274d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner // will be available to initialize the accumulator. 275d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner if (Argument *Arg = dyn_cast<Argument>(V)) { 276d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner // Figure out which argument number this is... 277d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner unsigned ArgNo = 0; 278d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner Function *F = CI->getParent()->getParent(); 279e4d5c441e04bdc00ccf1804744af670655123b07Chris Lattner for (Function::arg_iterator AI = F->arg_begin(); &*AI != Arg; ++AI) 280d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner ++ArgNo; 281fd93908ae8b9684fe71c239e3c6cfe13ff6a2663Misha Brukman 282d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner // If we are passing this argument into call as the corresponding 283d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner // argument operand, then the argument is dynamically constant. 284d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner // Otherwise, we cannot transform this function safely. 285de9f5452d3ae894bb7fdd455cec5af50e2560aa5Gabor Greif if (CI->getArgOperand(ArgNo) == Arg) 286d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner return true; 287d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner } 288f80fcd00b3590626a6110fe5fbe9b5fd2a8be1aeNick Lewycky 289f80fcd00b3590626a6110fe5fbe9b5fd2a8be1aeNick Lewycky // Switch cases are always constant integers. If the value is being switched 290f80fcd00b3590626a6110fe5fbe9b5fd2a8be1aeNick Lewycky // on and the return is only reachable from one of its cases, it's 291f80fcd00b3590626a6110fe5fbe9b5fd2a8be1aeNick Lewycky // effectively constant. 292f80fcd00b3590626a6110fe5fbe9b5fd2a8be1aeNick Lewycky if (BasicBlock *UniquePred = RI->getParent()->getUniquePredecessor()) 293f80fcd00b3590626a6110fe5fbe9b5fd2a8be1aeNick Lewycky if (SwitchInst *SI = dyn_cast<SwitchInst>(UniquePred->getTerminator())) 294f80fcd00b3590626a6110fe5fbe9b5fd2a8be1aeNick Lewycky if (SI->getCondition() == V) 295f80fcd00b3590626a6110fe5fbe9b5fd2a8be1aeNick Lewycky return SI->getDefaultDest() != RI->getParent(); 296f80fcd00b3590626a6110fe5fbe9b5fd2a8be1aeNick Lewycky 297d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner // Not a constant or immutable argument, we can't safely transform. 298d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner return false; 299d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner} 300d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner 301d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner// getCommonReturnValue - Check to see if the function containing the specified 302d50e9e2566479301e687fc81e16dab7e3c2b50eaDuncan Sands// tail call consistently returns the same runtime-constant value at all exit 303d50e9e2566479301e687fc81e16dab7e3c2b50eaDuncan Sands// points except for IgnoreRI. If so, return the returned value. 304d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner// 305d50e9e2566479301e687fc81e16dab7e3c2b50eaDuncan Sandsstatic Value *getCommonReturnValue(ReturnInst *IgnoreRI, CallInst *CI) { 306d50e9e2566479301e687fc81e16dab7e3c2b50eaDuncan Sands Function *F = CI->getParent()->getParent(); 307d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner Value *ReturnedValue = 0; 308d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner 309b5d84d13bc338efc4eeed87d19c49dfaed38e036Chris Lattner for (Function::iterator BBI = F->begin(), E = F->end(); BBI != E; ++BBI) { 310b5d84d13bc338efc4eeed87d19c49dfaed38e036Chris Lattner ReturnInst *RI = dyn_cast<ReturnInst>(BBI->getTerminator()); 311b5d84d13bc338efc4eeed87d19c49dfaed38e036Chris Lattner if (RI == 0 || RI == IgnoreRI) continue; 312b5d84d13bc338efc4eeed87d19c49dfaed38e036Chris Lattner 313b5d84d13bc338efc4eeed87d19c49dfaed38e036Chris Lattner // We can only perform this transformation if the value returned is 314b5d84d13bc338efc4eeed87d19c49dfaed38e036Chris Lattner // evaluatable at the start of the initial invocation of the function, 315b5d84d13bc338efc4eeed87d19c49dfaed38e036Chris Lattner // instead of at the end of the evaluation. 316b5d84d13bc338efc4eeed87d19c49dfaed38e036Chris Lattner // 317b5d84d13bc338efc4eeed87d19c49dfaed38e036Chris Lattner Value *RetOp = RI->getOperand(0); 318b5d84d13bc338efc4eeed87d19c49dfaed38e036Chris Lattner if (!isDynamicConstant(RetOp, CI, RI)) 319b5d84d13bc338efc4eeed87d19c49dfaed38e036Chris Lattner return 0; 320b5d84d13bc338efc4eeed87d19c49dfaed38e036Chris Lattner 321b5d84d13bc338efc4eeed87d19c49dfaed38e036Chris Lattner if (ReturnedValue && RetOp != ReturnedValue) 322b5d84d13bc338efc4eeed87d19c49dfaed38e036Chris Lattner return 0; // Cannot transform if differing values are returned. 323b5d84d13bc338efc4eeed87d19c49dfaed38e036Chris Lattner ReturnedValue = RetOp; 324b5d84d13bc338efc4eeed87d19c49dfaed38e036Chris Lattner } 325d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner return ReturnedValue; 326d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner} 3277152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner 328543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner/// CanTransformAccumulatorRecursion - If the specified instruction can be 329543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner/// transformed using accumulator recursion elimination, return the constant 330543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner/// which is the start of the accumulator value. Otherwise return null. 331543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner/// 332543d622ef7505910c1cdc09ada0ab797c3437590Chris LattnerValue *TailCallElim::CanTransformAccumulatorRecursion(Instruction *I, 333543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner CallInst *CI) { 33424080a98786cf393740cd035e27dd16c12827892Duncan Sands if (!I->isAssociative() || !I->isCommutative()) return 0; 335543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner assert(I->getNumOperands() == 2 && 33624080a98786cf393740cd035e27dd16c12827892Duncan Sands "Associative/commutative operations should have 2 args!"); 337543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner 338b5d84d13bc338efc4eeed87d19c49dfaed38e036Chris Lattner // Exactly one operand should be the result of the call instruction. 33907e6e56f57e8781a8d7bc601cc9034a3741d84c2Anton Korobeynikov if ((I->getOperand(0) == CI && I->getOperand(1) == CI) || 34007e6e56f57e8781a8d7bc601cc9034a3741d84c2Anton Korobeynikov (I->getOperand(0) != CI && I->getOperand(1) != CI)) 341543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner return 0; 342543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner 343543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // The only user of this instruction we allow is a single return instruction. 344543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner if (!I->hasOneUse() || !isa<ReturnInst>(I->use_back())) 345543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner return 0; 346543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner 347543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // Ok, now we have to check all of the other return instructions in this 348543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // function. If they return non-constants or differing values, then we cannot 349543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // transform the function safely. 350d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner return getCommonReturnValue(cast<ReturnInst>(I->use_back()), CI); 351543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner} 352543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner 353c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Chengstatic Instruction *FirstNonDbg(BasicBlock::iterator I) { 354c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng while (isa<DbgInfoIntrinsic>(I)) 355c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng ++I; 356c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng return &*I; 357c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng} 358c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng 359c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan ChengCallInst* 360c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan ChengTailCallElim::FindTRECandidate(Instruction *TI, 361c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng bool CannotTailCallElimCallsMarkedTail) { 362c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng BasicBlock *BB = TI->getParent(); 3637152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner Function *F = BB->getParent(); 3647152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner 365c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng if (&BB->front() == TI) // Make sure there is something before the terminator. 366c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng return 0; 3678d9455d4e4f63c368f17b74a36b472fc61685310Chris Lattner 3687152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner // Scan backwards from the return, checking to see if there is a tail call in 3697152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner // this block. If so, set CI to it. 370c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng CallInst *CI = 0; 371c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng BasicBlock::iterator BBI = TI; 372c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng while (true) { 3737152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner CI = dyn_cast<CallInst>(BBI); 3747152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner if (CI && CI->getCalledFunction() == F) 3757152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner break; 3767152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner 3777152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner if (BBI == BB->begin()) 378c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng return 0; // Didn't find a potential tail call. 3797152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner --BBI; 3807152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner } 3817152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner 382ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner // If this call is marked as a tail call, and if there are dynamic allocas in 383ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner // the function, we cannot perform this optimization. 384ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner if (CI->isTailCall() && CannotTailCallElimCallsMarkedTail) 385c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng return 0; 386ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner 387ea25b48af33be42e19236d8eac26bd42b45bcc1bDan Gohman // As a special case, detect code like this: 388ea25b48af33be42e19236d8eac26bd42b45bcc1bDan Gohman // double fabs(double f) { return __builtin_fabs(f); } // a 'fabs' call 389ea25b48af33be42e19236d8eac26bd42b45bcc1bDan Gohman // and disable this xform in this case, because the code generator will 390ea25b48af33be42e19236d8eac26bd42b45bcc1bDan Gohman // lower the call to fabs into inline code. 391ea25b48af33be42e19236d8eac26bd42b45bcc1bDan Gohman if (BB == &F->getEntryBlock() && 392c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng FirstNonDbg(BB->front()) == CI && 393c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng FirstNonDbg(llvm::next(BB->begin())) == TI && 394ea25b48af33be42e19236d8eac26bd42b45bcc1bDan Gohman callIsSmall(F)) { 395ea25b48af33be42e19236d8eac26bd42b45bcc1bDan Gohman // A single-block function with just a call and a return. Check that 396ea25b48af33be42e19236d8eac26bd42b45bcc1bDan Gohman // the arguments match. 397ea25b48af33be42e19236d8eac26bd42b45bcc1bDan Gohman CallSite::arg_iterator I = CallSite(CI).arg_begin(), 398ea25b48af33be42e19236d8eac26bd42b45bcc1bDan Gohman E = CallSite(CI).arg_end(); 399ea25b48af33be42e19236d8eac26bd42b45bcc1bDan Gohman Function::arg_iterator FI = F->arg_begin(), 400ea25b48af33be42e19236d8eac26bd42b45bcc1bDan Gohman FE = F->arg_end(); 401ea25b48af33be42e19236d8eac26bd42b45bcc1bDan Gohman for (; I != E && FI != FE; ++I, ++FI) 402ea25b48af33be42e19236d8eac26bd42b45bcc1bDan Gohman if (*I != &*FI) break; 403ea25b48af33be42e19236d8eac26bd42b45bcc1bDan Gohman if (I == E && FI == FE) 404c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng return 0; 405ea25b48af33be42e19236d8eac26bd42b45bcc1bDan Gohman } 406ea25b48af33be42e19236d8eac26bd42b45bcc1bDan Gohman 407c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng return CI; 408c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng} 409c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng 410c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Chengbool TailCallElim::EliminateRecursiveTailCall(CallInst *CI, ReturnInst *Ret, 411c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng BasicBlock *&OldEntry, 412c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng bool &TailCallsAreMarkedTail, 413c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng SmallVector<PHINode*, 8> &ArgumentPHIs, 414c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng bool CannotTailCallElimCallsMarkedTail) { 41524080a98786cf393740cd035e27dd16c12827892Duncan Sands // If we are introducing accumulator recursion to eliminate operations after 41624080a98786cf393740cd035e27dd16c12827892Duncan Sands // the call instruction that are both associative and commutative, the initial 41724080a98786cf393740cd035e27dd16c12827892Duncan Sands // value for the accumulator is placed in this variable. If this value is set 41824080a98786cf393740cd035e27dd16c12827892Duncan Sands // then we actually perform accumulator recursion elimination instead of 419d0d3ccc827de69de3d9f666aa922f5f191219a06Duncan Sands // simple tail recursion elimination. If the operation is an LLVM instruction 420d0d3ccc827de69de3d9f666aa922f5f191219a06Duncan Sands // (eg: "add") then it is recorded in AccumulatorRecursionInstr. If not, then 421d0d3ccc827de69de3d9f666aa922f5f191219a06Duncan Sands // we are handling the case when the return instruction returns a constant C 422d0d3ccc827de69de3d9f666aa922f5f191219a06Duncan Sands // which is different to the constant returned by other return instructions 423d0d3ccc827de69de3d9f666aa922f5f191219a06Duncan Sands // (which is recorded in AccumulatorRecursionEliminationInitVal). This is a 424d0d3ccc827de69de3d9f666aa922f5f191219a06Duncan Sands // special case of accumulator recursion, the operation being "return C". 425543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner Value *AccumulatorRecursionEliminationInitVal = 0; 426543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner Instruction *AccumulatorRecursionInstr = 0; 427543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner 4287152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner // Ok, we found a potential tail call. We can currently only transform the 4297152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner // tail call if all of the instructions between the call and the return are 4307152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner // movable to above the call itself, leaving the call next to the return. 4317152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner // Check that this is the case now. 432c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng BasicBlock::iterator BBI = CI; 433c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng for (++BBI; &*BBI != Ret; ++BBI) { 434b5d84d13bc338efc4eeed87d19c49dfaed38e036Chris Lattner if (CanMoveAboveCall(BBI, CI)) continue; 435b5d84d13bc338efc4eeed87d19c49dfaed38e036Chris Lattner 436b5d84d13bc338efc4eeed87d19c49dfaed38e036Chris Lattner // If we can't move the instruction above the call, it might be because it 4377a2bdde0a0eebcd2125055e0eacaca040f0b766cChris Lattner // is an associative and commutative operation that could be transformed 438b5d84d13bc338efc4eeed87d19c49dfaed38e036Chris Lattner // using accumulator recursion elimination. Check to see if this is the 439b5d84d13bc338efc4eeed87d19c49dfaed38e036Chris Lattner // case, and if so, remember the initial accumulator value for later. 440b5d84d13bc338efc4eeed87d19c49dfaed38e036Chris Lattner if ((AccumulatorRecursionEliminationInitVal = 441b5d84d13bc338efc4eeed87d19c49dfaed38e036Chris Lattner CanTransformAccumulatorRecursion(BBI, CI))) { 442b5d84d13bc338efc4eeed87d19c49dfaed38e036Chris Lattner // Yes, this is accumulator recursion. Remember which instruction 443b5d84d13bc338efc4eeed87d19c49dfaed38e036Chris Lattner // accumulates. 444b5d84d13bc338efc4eeed87d19c49dfaed38e036Chris Lattner AccumulatorRecursionInstr = BBI; 445b5d84d13bc338efc4eeed87d19c49dfaed38e036Chris Lattner } else { 446b5d84d13bc338efc4eeed87d19c49dfaed38e036Chris Lattner return false; // Otherwise, we cannot eliminate the tail recursion! 447543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner } 448b5d84d13bc338efc4eeed87d19c49dfaed38e036Chris Lattner } 4497152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner 4507152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner // We can only transform call/return pairs that either ignore the return value 451d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner // of the call and return void, ignore the value of the call and return a 452d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner // constant, return the value returned by the tail call, or that are being 453d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner // accumulator recursion variable eliminated. 454826c49132a9cba1e08a5fce78d05561d9a3746ceDevang Patel if (Ret->getNumOperands() == 1 && Ret->getReturnValue() != CI && 4553b5f45042b17ad52815e3dd6c0c1df99f196dd04Chris Lattner !isa<UndefValue>(Ret->getReturnValue()) && 456d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner AccumulatorRecursionEliminationInitVal == 0 && 457d0d3ccc827de69de3d9f666aa922f5f191219a06Duncan Sands !getCommonReturnValue(0, CI)) { 458d0d3ccc827de69de3d9f666aa922f5f191219a06Duncan Sands // One case remains that we are able to handle: the current return 459d0d3ccc827de69de3d9f666aa922f5f191219a06Duncan Sands // instruction returns a constant, and all other return instructions 460d0d3ccc827de69de3d9f666aa922f5f191219a06Duncan Sands // return a different constant. 461d0d3ccc827de69de3d9f666aa922f5f191219a06Duncan Sands if (!isDynamicConstant(Ret->getReturnValue(), CI, Ret)) 462d0d3ccc827de69de3d9f666aa922f5f191219a06Duncan Sands return false; // Current return instruction does not return a constant. 463d0d3ccc827de69de3d9f666aa922f5f191219a06Duncan Sands // Check that all other return instructions return a common constant. If 464d0d3ccc827de69de3d9f666aa922f5f191219a06Duncan Sands // so, record it in AccumulatorRecursionEliminationInitVal. 465d0d3ccc827de69de3d9f666aa922f5f191219a06Duncan Sands AccumulatorRecursionEliminationInitVal = getCommonReturnValue(Ret, CI); 466d0d3ccc827de69de3d9f666aa922f5f191219a06Duncan Sands if (!AccumulatorRecursionEliminationInitVal) 467d0d3ccc827de69de3d9f666aa922f5f191219a06Duncan Sands return false; 468d0d3ccc827de69de3d9f666aa922f5f191219a06Duncan Sands } 4697152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner 470c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng BasicBlock *BB = Ret->getParent(); 471c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng Function *F = BB->getParent(); 472c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng 4737152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner // OK! We can transform this tail call. If this is the first one found, 4747152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner // create the new entry block, allowing us to branch back to the old entry. 4757152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner if (OldEntry == 0) { 4767152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner OldEntry = &F->getEntryBlock(); 4771d0be15f89cb5056e20e2d24faa8d6afb1573bcaOwen Anderson BasicBlock *NewEntry = BasicBlock::Create(F->getContext(), "", F, OldEntry); 4786934a04a8c15e9971cd1ea4d5c8df2d7afdd5be5Chris Lattner NewEntry->takeName(OldEntry); 4796934a04a8c15e9971cd1ea4d5c8df2d7afdd5be5Chris Lattner OldEntry->setName("tailrecurse"); 480051a950000e21935165db56695e35bade668193bGabor Greif BranchInst::Create(OldEntry, NewEntry); 481fd93908ae8b9684fe71c239e3c6cfe13ff6a2663Misha Brukman 482ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner // If this tail call is marked 'tail' and if there are any allocas in the 483ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner // entry block, move them up to the new entry block. 484ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner TailCallsAreMarkedTail = CI->isTailCall(); 485ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner if (TailCallsAreMarkedTail) 486ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner // Move all fixed sized allocas from OldEntry to NewEntry. 487ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner for (BasicBlock::iterator OEBI = OldEntry->begin(), E = OldEntry->end(), 488ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner NEBI = NewEntry->begin(); OEBI != E; ) 489ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner if (AllocaInst *AI = dyn_cast<AllocaInst>(OEBI++)) 490ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner if (isa<ConstantInt>(AI->getArraySize())) 4914bc5f8071a28b6fc4f4c2207dd03a5f747d0d84bChris Lattner AI->moveBefore(NEBI); 492ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner 4937152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner // Now that we have created a new block, which jumps to the entry 4947152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner // block, insert a PHI node for each argument of the function. 4957152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner // For now, we initialize each PHI to only have the real arguments 4967152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner // which are passed in. 4977152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner Instruction *InsertPos = OldEntry->begin(); 4987f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattner for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(); 4997f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattner I != E; ++I) { 5003ecfc861b4365f341c5c969b40e1afccde676e6fJay Foad PHINode *PN = PHINode::Create(I->getType(), 2, 501b1dbcd886a4b5597a839f299054b78b33fb2d6dfGabor Greif I->getName() + ".tr", InsertPos); 5027152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner I->replaceAllUsesWith(PN); // Everyone use the PHI node now! 5037152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner PN->addIncoming(I, NewEntry); 5047152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner ArgumentPHIs.push_back(PN); 5057152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner } 5067152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner } 507fd93908ae8b9684fe71c239e3c6cfe13ff6a2663Misha Brukman 508ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner // If this function has self recursive calls in the tail position where some 509ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner // are marked tail and some are not, only transform one flavor or another. We 510ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner // have to choose whether we move allocas in the entry block to the new entry 511ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner // block or not, so we can't make a good choice for both. NOTE: We could do 512ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner // slightly better here in the case that the function has no entry block 513ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner // allocas. 514ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner if (TailCallsAreMarkedTail && !CI->isTailCall()) 515ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner return false; 516ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner 5177152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner // Ok, now that we know we have a pseudo-entry block WITH all of the 5187152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner // required PHI nodes, add entries into the PHI node for the actual 5197152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner // parameters passed into the tail-recursive call. 520407014f9a5f05f5a5867e5992a036358acc4a441Gabor Greif for (unsigned i = 0, e = CI->getNumArgOperands(); i != e; ++i) 521de9f5452d3ae894bb7fdd455cec5af50e2560aa5Gabor Greif ArgumentPHIs[i]->addIncoming(CI->getArgOperand(i), BB); 522fd93908ae8b9684fe71c239e3c6cfe13ff6a2663Misha Brukman 523543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // If we are introducing an accumulator variable to eliminate the recursion, 524543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // do so now. Note that we _know_ that no subsequent tail recursion 525543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // eliminations will happen on this function because of the way the 526543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // accumulator recursion predicate is set up. 527543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // 528543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner if (AccumulatorRecursionEliminationInitVal) { 529543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner Instruction *AccRecInstr = AccumulatorRecursionInstr; 530543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // Start by inserting a new PHI node for the accumulator. 531d8b4fb4aab4d6fedb2b14bed1b846451b17bde7cJay Foad pred_iterator PB = pred_begin(OldEntry), PE = pred_end(OldEntry); 532d0d3ccc827de69de3d9f666aa922f5f191219a06Duncan Sands PHINode *AccPN = 533d0d3ccc827de69de3d9f666aa922f5f191219a06Duncan Sands PHINode::Create(AccumulatorRecursionEliminationInitVal->getType(), 5343ecfc861b4365f341c5c969b40e1afccde676e6fJay Foad std::distance(PB, PE) + 1, 535d0d3ccc827de69de3d9f666aa922f5f191219a06Duncan Sands "accumulator.tr", OldEntry->begin()); 536543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner 537543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // Loop over all of the predecessors of the tail recursion block. For the 538543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // real entry into the function we seed the PHI with the initial value, 539543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // computed earlier. For any other existing branches to this block (due to 540543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // other tail recursions eliminated) the accumulator is not modified. 541543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // Because we haven't added the branch in the current block to OldEntry yet, 542543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // it will not show up as a predecessor. 543d8b4fb4aab4d6fedb2b14bed1b846451b17bde7cJay Foad for (pred_iterator PI = PB; PI != PE; ++PI) { 544a8b9df7bd96e0b0bc6dec448d30b7d72180b6595Gabor Greif BasicBlock *P = *PI; 545a8b9df7bd96e0b0bc6dec448d30b7d72180b6595Gabor Greif if (P == &F->getEntryBlock()) 546a8b9df7bd96e0b0bc6dec448d30b7d72180b6595Gabor Greif AccPN->addIncoming(AccumulatorRecursionEliminationInitVal, P); 547543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner else 548a8b9df7bd96e0b0bc6dec448d30b7d72180b6595Gabor Greif AccPN->addIncoming(AccPN, P); 549543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner } 550543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner 551d0d3ccc827de69de3d9f666aa922f5f191219a06Duncan Sands if (AccRecInstr) { 552d0d3ccc827de69de3d9f666aa922f5f191219a06Duncan Sands // Add an incoming argument for the current block, which is computed by 553d0d3ccc827de69de3d9f666aa922f5f191219a06Duncan Sands // our associative and commutative accumulator instruction. 554d0d3ccc827de69de3d9f666aa922f5f191219a06Duncan Sands AccPN->addIncoming(AccRecInstr, BB); 555d0d3ccc827de69de3d9f666aa922f5f191219a06Duncan Sands 556d0d3ccc827de69de3d9f666aa922f5f191219a06Duncan Sands // Next, rewrite the accumulator recursion instruction so that it does not 557d0d3ccc827de69de3d9f666aa922f5f191219a06Duncan Sands // use the result of the call anymore, instead, use the PHI node we just 558d0d3ccc827de69de3d9f666aa922f5f191219a06Duncan Sands // inserted. 559d0d3ccc827de69de3d9f666aa922f5f191219a06Duncan Sands AccRecInstr->setOperand(AccRecInstr->getOperand(0) != CI, AccPN); 560d0d3ccc827de69de3d9f666aa922f5f191219a06Duncan Sands } else { 561d0d3ccc827de69de3d9f666aa922f5f191219a06Duncan Sands // Add an incoming argument for the current block, which is just the 562d0d3ccc827de69de3d9f666aa922f5f191219a06Duncan Sands // constant returned by the current return instruction. 563d0d3ccc827de69de3d9f666aa922f5f191219a06Duncan Sands AccPN->addIncoming(Ret->getReturnValue(), BB); 564d0d3ccc827de69de3d9f666aa922f5f191219a06Duncan Sands } 565543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner 566543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // Finally, rewrite any return instructions in the program to return the PHI 567543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // node instead of the "initval" that they do currently. This loop will 568543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // actually rewrite the return value we are destroying, but that's ok. 569543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner for (Function::iterator BBI = F->begin(), E = F->end(); BBI != E; ++BBI) 570543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner if (ReturnInst *RI = dyn_cast<ReturnInst>(BBI->getTerminator())) 571543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner RI->setOperand(0, AccPN); 572543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner ++NumAccumAdded; 573543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner } 574543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner 5757152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner // Now that all of the PHI nodes are in place, remove the call and 5767152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner // ret instructions, replacing them with an unconditional branch. 57781199d2545112fcff5a6e055eb71e2a4950192a7Devang Patel BranchInst *NewBI = BranchInst::Create(OldEntry, Ret); 57881199d2545112fcff5a6e055eb71e2a4950192a7Devang Patel NewBI->setDebugLoc(CI->getDebugLoc()); 57981199d2545112fcff5a6e055eb71e2a4950192a7Devang Patel 5807152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner BB->getInstList().erase(Ret); // Remove return. 5817152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner BB->getInstList().erase(CI); // Remove call. 582543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner ++NumEliminated; 5837152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner return true; 5847152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner} 585c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng 586c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Chengbool TailCallElim::FoldReturnAndProcessPred(BasicBlock *BB, 587c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng ReturnInst *Ret, BasicBlock *&OldEntry, 588c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng bool &TailCallsAreMarkedTail, 589c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng SmallVector<PHINode*, 8> &ArgumentPHIs, 590c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng bool CannotTailCallElimCallsMarkedTail) { 591c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng bool Change = false; 592c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng 593c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng // If the return block contains nothing but the return and PHI's, 594c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng // there might be an opportunity to duplicate the return in its 595c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng // predecessors and perform TRC there. Look for predecessors that end 596c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng // in unconditional branch and recursive call(s). 597c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng SmallVector<BranchInst*, 8> UncondBranchPreds; 598c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) { 599c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng BasicBlock *Pred = *PI; 600c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng TerminatorInst *PTI = Pred->getTerminator(); 601c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng if (BranchInst *BI = dyn_cast<BranchInst>(PTI)) 602c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng if (BI->isUnconditional()) 603c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng UncondBranchPreds.push_back(BI); 604c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng } 605c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng 606c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng while (!UncondBranchPreds.empty()) { 607c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng BranchInst *BI = UncondBranchPreds.pop_back_val(); 608c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng BasicBlock *Pred = BI->getParent(); 609c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng if (CallInst *CI = FindTRECandidate(BI, CannotTailCallElimCallsMarkedTail)){ 610c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng DEBUG(dbgs() << "FOLDING: " << *BB 611c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng << "INTO UNCOND BRANCH PRED: " << *Pred); 612c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng EliminateRecursiveTailCall(CI, FoldReturnIntoUncondBranch(Ret, BB, Pred), 613c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng OldEntry, TailCallsAreMarkedTail, ArgumentPHIs, 614c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng CannotTailCallElimCallsMarkedTail); 61560f5ad46c2147af79035a43e5745e46376124780Evan Cheng ++NumRetDuped; 616c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng Change = true; 617c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng } 618c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng } 619c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng 620c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng return Change; 621c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng} 622c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng 623c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Chengbool TailCallElim::ProcessReturningBlock(ReturnInst *Ret, BasicBlock *&OldEntry, 624c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng bool &TailCallsAreMarkedTail, 625c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng SmallVector<PHINode*, 8> &ArgumentPHIs, 626c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng bool CannotTailCallElimCallsMarkedTail) { 627c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng CallInst *CI = FindTRECandidate(Ret, CannotTailCallElimCallsMarkedTail); 628c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng if (!CI) 629c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng return false; 630c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng 631c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng return EliminateRecursiveTailCall(CI, Ret, OldEntry, TailCallsAreMarkedTail, 632c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng ArgumentPHIs, 633c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng CannotTailCallElimCallsMarkedTail); 634c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng} 635