TailRecursionElimination.cpp revision 337c0811381a48b75aec204d96090779fec6606e
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. 392240d2b3f7b9f5835868c83ce78d125d1b65212bChris Lattner// 2. Tail recursion is only performed if the call immediately preceeds 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" 622240d2b3f7b9f5835868c83ce78d125d1b65212bChris Lattner#include "llvm/Pass.h" 630cade261322242132905914f613d25d16e1a9ff6Nick Lewycky#include "llvm/Analysis/CaptureTracking.h" 64ea25b48af33be42e19236d8eac26bd42b45bcc1bDan Gohman#include "llvm/Analysis/InlineCost.h" 65cdbd99262286e96729007ac535cd430ecb3d38acDuncan Sands#include "llvm/Analysis/InstructionSimplify.h" 66dd9344f3face8f1978a7f9f393c31b628144d1f6Dan Gohman#include "llvm/Analysis/Loads.h" 67ea25b48af33be42e19236d8eac26bd42b45bcc1bDan Gohman#include "llvm/Support/CallSite.h" 68543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner#include "llvm/Support/CFG.h" 69c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng#include "llvm/Support/Debug.h" 70337c0811381a48b75aec204d96090779fec6606eFrancois Pichet#include "llvm/Support/raw_ostream.h" 71551ccae044b0ff658fe629dd67edd5ffe75d10e8Reid Spencer#include "llvm/ADT/Statistic.h" 72c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng#include "llvm/ADT/STLExtras.h" 73f8485c643412dbff46fe87ea2867445169a5c28eChris Lattnerusing namespace llvm; 74d0fde30ce850b78371fd1386338350591f9ff494Brian Gaeke 750e5f499638c8d277b9dc4a4385712177c53b5681Chris LattnerSTATISTIC(NumEliminated, "Number of tail calls removed"); 7660f5ad46c2147af79035a43e5745e46376124780Evan ChengSTATISTIC(NumRetDuped, "Number of return duplicated"); 770e5f499638c8d277b9dc4a4385712177c53b5681Chris LattnerSTATISTIC(NumAccumAdded, "Number of accumulators introduced"); 782240d2b3f7b9f5835868c83ce78d125d1b65212bChris Lattner 790e5f499638c8d277b9dc4a4385712177c53b5681Chris Lattnernamespace { 803e8b6631e67e01e4960a7ba4668a50c596607473Chris Lattner struct TailCallElim : public FunctionPass { 81ecd94c804a563f2a86572dcf1d2e81f397e19daaNick Lewycky static char ID; // Pass identification, replacement for typeid 82081c34b725980f995be9080eaec24cd3dfaaf065Owen Anderson TailCallElim() : FunctionPass(ID) { 83081c34b725980f995be9080eaec24cd3dfaaf065Owen Anderson initializeTailCallElimPass(*PassRegistry::getPassRegistry()); 84081c34b725980f995be9080eaec24cd3dfaaf065Owen Anderson } 85794fd75c67a2cdc128d67342c6d88a504d186896Devang Patel 862240d2b3f7b9f5835868c83ce78d125d1b65212bChris Lattner virtual bool runOnFunction(Function &F); 877152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner 887152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner private: 89c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng CallInst *FindTRECandidate(Instruction *I, 90c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng bool CannotTailCallElimCallsMarkedTail); 91c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng bool EliminateRecursiveTailCall(CallInst *CI, ReturnInst *Ret, 92c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng BasicBlock *&OldEntry, 93c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng bool &TailCallsAreMarkedTail, 94c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng SmallVector<PHINode*, 8> &ArgumentPHIs, 95c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng bool CannotTailCallElimCallsMarkedTail); 96c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng bool FoldReturnAndProcessPred(BasicBlock *BB, 97c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng ReturnInst *Ret, BasicBlock *&OldEntry, 98c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng bool &TailCallsAreMarkedTail, 99c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng SmallVector<PHINode*, 8> &ArgumentPHIs, 100c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng bool CannotTailCallElimCallsMarkedTail); 1017152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner bool ProcessReturningBlock(ReturnInst *RI, BasicBlock *&OldEntry, 102ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner bool &TailCallsAreMarkedTail, 1030cade261322242132905914f613d25d16e1a9ff6Nick Lewycky SmallVector<PHINode*, 8> &ArgumentPHIs, 104ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner bool CannotTailCallElimCallsMarkedTail); 1057152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner bool CanMoveAboveCall(Instruction *I, CallInst *CI); 106543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner Value *CanTransformAccumulatorRecursion(Instruction *I, CallInst *CI); 1072240d2b3f7b9f5835868c83ce78d125d1b65212bChris Lattner }; 1082240d2b3f7b9f5835868c83ce78d125d1b65212bChris Lattner} 1092240d2b3f7b9f5835868c83ce78d125d1b65212bChris Lattner 110844731a7f1909f55935e3514c9e713a62d67662eDan Gohmanchar TailCallElim::ID = 0; 111d13db2c59cc94162d6cf0a04187d408bfef6d4a7Owen AndersonINITIALIZE_PASS(TailCallElim, "tailcallelim", 112ce665bd2e2b581ab0858d1afe359192bac96b868Owen Anderson "Tail Call Elimination", false, false) 113844731a7f1909f55935e3514c9e713a62d67662eDan Gohman 114d0fde30ce850b78371fd1386338350591f9ff494Brian Gaeke// Public interface to the TailCallElimination pass 115f8485c643412dbff46fe87ea2867445169a5c28eChris LattnerFunctionPass *llvm::createTailCallEliminationPass() { 116f8485c643412dbff46fe87ea2867445169a5c28eChris Lattner return new TailCallElim(); 117f8485c643412dbff46fe87ea2867445169a5c28eChris Lattner} 1183fc6ef1bb96d9a3194cef667a2d3cbc94e3fb189Chris Lattner 119cb19438f63019eb557c1fbaeae8a6de78b03c584Nick Lewycky/// AllocaMightEscapeToCalls - Return true if this alloca may be accessed by 120cb19438f63019eb557c1fbaeae8a6de78b03c584Nick Lewycky/// callees of this function. We only do very simple analysis right now, this 121cb19438f63019eb557c1fbaeae8a6de78b03c584Nick Lewycky/// could be expanded in the future to use mod/ref information for particular 122cb19438f63019eb557c1fbaeae8a6de78b03c584Nick Lewycky/// call sites if desired. 123cb19438f63019eb557c1fbaeae8a6de78b03c584Nick Lewyckystatic bool AllocaMightEscapeToCalls(AllocaInst *AI) { 124cb19438f63019eb557c1fbaeae8a6de78b03c584Nick Lewycky // FIXME: do simple 'address taken' analysis. 125cb19438f63019eb557c1fbaeae8a6de78b03c584Nick Lewycky return true; 126cb19438f63019eb557c1fbaeae8a6de78b03c584Nick Lewycky} 127cb19438f63019eb557c1fbaeae8a6de78b03c584Nick Lewycky 1280cade261322242132905914f613d25d16e1a9ff6Nick Lewycky/// CheckForEscapingAllocas - Scan the specified basic block for alloca 1297f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattner/// instructions. If it contains any that might be accessed by calls, return 1307f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattner/// true. 131ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattnerstatic bool CheckForEscapingAllocas(BasicBlock *BB, 132ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner bool &CannotTCETailMarkedCall) { 133ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner bool RetVal = false; 1347f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattner for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) 135ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner if (AllocaInst *AI = dyn_cast<AllocaInst>(I)) { 136cb19438f63019eb557c1fbaeae8a6de78b03c584Nick Lewycky RetVal |= AllocaMightEscapeToCalls(AI); 137ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner 138ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner // If this alloca is in the body of the function, or if it is a variable 139ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner // sized allocation, we cannot tail call eliminate calls marked 'tail' 140ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner // with this mechanism. 141ecb7a77885b174cf4d001a9b48533b3979e7810dDan Gohman if (BB != &BB->getParent()->getEntryBlock() || 142ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner !isa<ConstantInt>(AI->getArraySize())) 143ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner CannotTCETailMarkedCall = true; 144ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner } 145ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner return RetVal; 1467f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattner} 1477f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattner 1482240d2b3f7b9f5835868c83ce78d125d1b65212bChris Lattnerbool TailCallElim::runOnFunction(Function &F) { 1492240d2b3f7b9f5835868c83ce78d125d1b65212bChris Lattner // If this function is a varargs function, we won't be able to PHI the args 1502240d2b3f7b9f5835868c83ce78d125d1b65212bChris Lattner // right, so don't even try to convert it... 1512240d2b3f7b9f5835868c83ce78d125d1b65212bChris Lattner if (F.getFunctionType()->isVarArg()) return false; 1522240d2b3f7b9f5835868c83ce78d125d1b65212bChris Lattner 1532240d2b3f7b9f5835868c83ce78d125d1b65212bChris Lattner BasicBlock *OldEntry = 0; 154ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner bool TailCallsAreMarkedTail = false; 1550cade261322242132905914f613d25d16e1a9ff6Nick Lewycky SmallVector<PHINode*, 8> ArgumentPHIs; 1562240d2b3f7b9f5835868c83ce78d125d1b65212bChris Lattner bool MadeChange = false; 1577f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattner bool FunctionContainsEscapingAllocas = false; 1587f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattner 159ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner // CannotTCETailMarkedCall - If true, we cannot perform TCE on tail calls 160ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner // marked with the 'tail' attribute, because doing so would cause the stack 161ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner // size to increase (real TCE would deallocate variable sized allocas, TCE 162ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner // doesn't). 163ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner bool CannotTCETailMarkedCall = false; 164ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner 1657f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattner // Loop over the function, looking for any returning blocks, and keeping track 1667f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattner // of whether this function has any non-trivially used allocas. 1677f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattner for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) { 168ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner if (FunctionContainsEscapingAllocas && CannotTCETailMarkedCall) 169ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner break; 17000b16889ab461b7ecef1c91ade101186b7f1fce2Jeff Cohen 1714c0e4cdc40bbf94766242294fe386f4eb2d32d2eChris Lattner FunctionContainsEscapingAllocas |= 172ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner CheckForEscapingAllocas(BB, CannotTCETailMarkedCall); 1737f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattner } 17432b1e87f111d79f3f5b0e86c8f138c02bef8aa18Chris Lattner 17532b1e87f111d79f3f5b0e86c8f138c02bef8aa18Chris Lattner /// FIXME: The code generator produces really bad code when an 'escaping 17632b1e87f111d79f3f5b0e86c8f138c02bef8aa18Chris Lattner /// alloca' is changed from being a static alloca to being a dynamic alloca. 17732b1e87f111d79f3f5b0e86c8f138c02bef8aa18Chris Lattner /// Until this is resolved, disable this transformation if that would ever 17832b1e87f111d79f3f5b0e86c8f138c02bef8aa18Chris Lattner /// happen. This bug is PR962. 17932b1e87f111d79f3f5b0e86c8f138c02bef8aa18Chris Lattner if (FunctionContainsEscapingAllocas) 18032b1e87f111d79f3f5b0e86c8f138c02bef8aa18Chris Lattner return false; 181fd93908ae8b9684fe71c239e3c6cfe13ff6a2663Misha Brukman 182ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner // Second pass, change any tail calls to loops. 183c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) { 184c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng if (ReturnInst *Ret = dyn_cast<ReturnInst>(BB->getTerminator())) { 185c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng bool Change = ProcessReturningBlock(Ret, OldEntry, TailCallsAreMarkedTail, 186ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner ArgumentPHIs,CannotTCETailMarkedCall); 187c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng if (!Change && BB->getFirstNonPHIOrDbg() == Ret) 188c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng Change = FoldReturnAndProcessPred(BB, Ret, OldEntry, 189c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng TailCallsAreMarkedTail, ArgumentPHIs, 190c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng CannotTCETailMarkedCall); 191c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng MadeChange |= Change; 192c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng } 193c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng } 194ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner 195cf2f89251d45bc9783917874adb9029f71d50068Chris Lattner // If we eliminated any tail recursions, it's possible that we inserted some 196cf2f89251d45bc9783917874adb9029f71d50068Chris Lattner // silly PHI nodes which just merge an initial value (the incoming operand) 197cf2f89251d45bc9783917874adb9029f71d50068Chris Lattner // with themselves. Check to see if we did and clean up our mess if so. This 198cf2f89251d45bc9783917874adb9029f71d50068Chris Lattner // occurs when a function passes an argument straight through to its tail 199cf2f89251d45bc9783917874adb9029f71d50068Chris Lattner // call. 200cf2f89251d45bc9783917874adb9029f71d50068Chris Lattner if (!ArgumentPHIs.empty()) { 201cf2f89251d45bc9783917874adb9029f71d50068Chris Lattner for (unsigned i = 0, e = ArgumentPHIs.size(); i != e; ++i) { 202cf2f89251d45bc9783917874adb9029f71d50068Chris Lattner PHINode *PN = ArgumentPHIs[i]; 203cf2f89251d45bc9783917874adb9029f71d50068Chris Lattner 204cf2f89251d45bc9783917874adb9029f71d50068Chris Lattner // If the PHI Node is a dynamic constant, replace it with the value it is. 205cdbd99262286e96729007ac535cd430ecb3d38acDuncan Sands if (Value *PNV = SimplifyInstruction(PN)) { 206ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner PN->replaceAllUsesWith(PNV); 207ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner PN->eraseFromParent(); 208cf2f89251d45bc9783917874adb9029f71d50068Chris Lattner } 209cf2f89251d45bc9783917874adb9029f71d50068Chris Lattner } 210cf2f89251d45bc9783917874adb9029f71d50068Chris Lattner } 211cf2f89251d45bc9783917874adb9029f71d50068Chris Lattner 2127f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattner // Finally, if this function contains no non-escaping allocas, mark all calls 2137f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattner // in the function as eligible for tail calls (there is no stack memory for 2147f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattner // them to access). 2157f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattner if (!FunctionContainsEscapingAllocas) 2167f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattner for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) 2177f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattner for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) 218febc81680c80a53f15f85b1812cba07fc179b9fdEvan Cheng if (CallInst *CI = dyn_cast<CallInst>(I)) { 219febc81680c80a53f15f85b1812cba07fc179b9fdEvan Cheng CI->setTailCall(); 220febc81680c80a53f15f85b1812cba07fc179b9fdEvan Cheng MadeChange = true; 221febc81680c80a53f15f85b1812cba07fc179b9fdEvan Cheng } 2227f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattner 2232240d2b3f7b9f5835868c83ce78d125d1b65212bChris Lattner return MadeChange; 2242240d2b3f7b9f5835868c83ce78d125d1b65212bChris Lattner} 2257152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner 2267152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner 227543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner/// CanMoveAboveCall - Return true if it is safe to move the specified 228543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner/// instruction from after the call to before the call, assuming that all 229543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner/// instructions between the call and this instruction are movable. 230543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner/// 2317152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattnerbool TailCallElim::CanMoveAboveCall(Instruction *I, CallInst *CI) { 2327152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner // FIXME: We can move load/store/call/free instructions above the call if the 2337152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner // call does not mod/ref the memory location being processed. 2346a35b40250735a50efe66c88414cdd3b79185019Chris Lattner if (I->mayHaveSideEffects()) // This also handles volatile loads. 2357152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner return false; 2366a35b40250735a50efe66c88414cdd3b79185019Chris Lattner 2370cade261322242132905914f613d25d16e1a9ff6Nick Lewycky if (LoadInst *L = dyn_cast<LoadInst>(I)) { 2386a35b40250735a50efe66c88414cdd3b79185019Chris Lattner // Loads may always be moved above calls without side effects. 2396a35b40250735a50efe66c88414cdd3b79185019Chris Lattner if (CI->mayHaveSideEffects()) { 2406a35b40250735a50efe66c88414cdd3b79185019Chris Lattner // Non-volatile loads may be moved above a call with side effects if it 2416a35b40250735a50efe66c88414cdd3b79185019Chris Lattner // does not write to memory and the load provably won't trap. 2426a35b40250735a50efe66c88414cdd3b79185019Chris Lattner // FIXME: Writes to memory only matter if they may alias the pointer 2436a35b40250735a50efe66c88414cdd3b79185019Chris Lattner // being loaded from. 2446a35b40250735a50efe66c88414cdd3b79185019Chris Lattner if (CI->mayWriteToMemory() || 24549db68fba01722ca032dc5170f8248a9d25f0199Bob Wilson !isSafeToLoadUnconditionally(L->getPointerOperand(), L, 24649db68fba01722ca032dc5170f8248a9d25f0199Bob Wilson L->getAlignment())) 2476a35b40250735a50efe66c88414cdd3b79185019Chris Lattner return false; 2486a35b40250735a50efe66c88414cdd3b79185019Chris Lattner } 2496a35b40250735a50efe66c88414cdd3b79185019Chris Lattner } 2507152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner 2517152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner // Otherwise, if this is a side-effect free instruction, check to make sure 2527152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner // that it does not use the return value of the call. If it doesn't use the 2537152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner // return value of the call, it must only use things that are defined before 2547152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner // the call, or movable instructions between the call and the instruction 2557152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner // itself. 2567152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) 2577152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner if (I->getOperand(i) == CI) 2587152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner return false; 2597152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner return true; 2607152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner} 2617152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner 262d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner// isDynamicConstant - Return true if the specified value is the same when the 263d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner// return would exit as it was when the initial iteration of the recursive 264d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner// function was executed. 265d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner// 266d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner// We currently handle static constants and arguments that are not modified as 267d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner// part of the recursion. 268d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner// 269f80fcd00b3590626a6110fe5fbe9b5fd2a8be1aeNick Lewyckystatic bool isDynamicConstant(Value *V, CallInst *CI, ReturnInst *RI) { 270d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner if (isa<Constant>(V)) return true; // Static constants are always dyn consts 271d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner 272d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner // Check to see if this is an immutable argument, if so, the value 273d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner // will be available to initialize the accumulator. 274d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner if (Argument *Arg = dyn_cast<Argument>(V)) { 275d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner // Figure out which argument number this is... 276d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner unsigned ArgNo = 0; 277d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner Function *F = CI->getParent()->getParent(); 278e4d5c441e04bdc00ccf1804744af670655123b07Chris Lattner for (Function::arg_iterator AI = F->arg_begin(); &*AI != Arg; ++AI) 279d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner ++ArgNo; 280fd93908ae8b9684fe71c239e3c6cfe13ff6a2663Misha Brukman 281d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner // If we are passing this argument into call as the corresponding 282d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner // argument operand, then the argument is dynamically constant. 283d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner // Otherwise, we cannot transform this function safely. 284de9f5452d3ae894bb7fdd455cec5af50e2560aa5Gabor Greif if (CI->getArgOperand(ArgNo) == Arg) 285d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner return true; 286d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner } 287f80fcd00b3590626a6110fe5fbe9b5fd2a8be1aeNick Lewycky 288f80fcd00b3590626a6110fe5fbe9b5fd2a8be1aeNick Lewycky // Switch cases are always constant integers. If the value is being switched 289f80fcd00b3590626a6110fe5fbe9b5fd2a8be1aeNick Lewycky // on and the return is only reachable from one of its cases, it's 290f80fcd00b3590626a6110fe5fbe9b5fd2a8be1aeNick Lewycky // effectively constant. 291f80fcd00b3590626a6110fe5fbe9b5fd2a8be1aeNick Lewycky if (BasicBlock *UniquePred = RI->getParent()->getUniquePredecessor()) 292f80fcd00b3590626a6110fe5fbe9b5fd2a8be1aeNick Lewycky if (SwitchInst *SI = dyn_cast<SwitchInst>(UniquePred->getTerminator())) 293f80fcd00b3590626a6110fe5fbe9b5fd2a8be1aeNick Lewycky if (SI->getCondition() == V) 294f80fcd00b3590626a6110fe5fbe9b5fd2a8be1aeNick Lewycky return SI->getDefaultDest() != RI->getParent(); 295f80fcd00b3590626a6110fe5fbe9b5fd2a8be1aeNick Lewycky 296d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner // Not a constant or immutable argument, we can't safely transform. 297d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner return false; 298d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner} 299d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner 300d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner// getCommonReturnValue - Check to see if the function containing the specified 301d50e9e2566479301e687fc81e16dab7e3c2b50eaDuncan Sands// tail call consistently returns the same runtime-constant value at all exit 302d50e9e2566479301e687fc81e16dab7e3c2b50eaDuncan Sands// points except for IgnoreRI. If so, return the returned value. 303d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner// 304d50e9e2566479301e687fc81e16dab7e3c2b50eaDuncan Sandsstatic Value *getCommonReturnValue(ReturnInst *IgnoreRI, CallInst *CI) { 305d50e9e2566479301e687fc81e16dab7e3c2b50eaDuncan Sands Function *F = CI->getParent()->getParent(); 306d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner Value *ReturnedValue = 0; 307d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner 308b5d84d13bc338efc4eeed87d19c49dfaed38e036Chris Lattner for (Function::iterator BBI = F->begin(), E = F->end(); BBI != E; ++BBI) { 309b5d84d13bc338efc4eeed87d19c49dfaed38e036Chris Lattner ReturnInst *RI = dyn_cast<ReturnInst>(BBI->getTerminator()); 310b5d84d13bc338efc4eeed87d19c49dfaed38e036Chris Lattner if (RI == 0 || RI == IgnoreRI) continue; 311b5d84d13bc338efc4eeed87d19c49dfaed38e036Chris Lattner 312b5d84d13bc338efc4eeed87d19c49dfaed38e036Chris Lattner // We can only perform this transformation if the value returned is 313b5d84d13bc338efc4eeed87d19c49dfaed38e036Chris Lattner // evaluatable at the start of the initial invocation of the function, 314b5d84d13bc338efc4eeed87d19c49dfaed38e036Chris Lattner // instead of at the end of the evaluation. 315b5d84d13bc338efc4eeed87d19c49dfaed38e036Chris Lattner // 316b5d84d13bc338efc4eeed87d19c49dfaed38e036Chris Lattner Value *RetOp = RI->getOperand(0); 317b5d84d13bc338efc4eeed87d19c49dfaed38e036Chris Lattner if (!isDynamicConstant(RetOp, CI, RI)) 318b5d84d13bc338efc4eeed87d19c49dfaed38e036Chris Lattner return 0; 319b5d84d13bc338efc4eeed87d19c49dfaed38e036Chris Lattner 320b5d84d13bc338efc4eeed87d19c49dfaed38e036Chris Lattner if (ReturnedValue && RetOp != ReturnedValue) 321b5d84d13bc338efc4eeed87d19c49dfaed38e036Chris Lattner return 0; // Cannot transform if differing values are returned. 322b5d84d13bc338efc4eeed87d19c49dfaed38e036Chris Lattner ReturnedValue = RetOp; 323b5d84d13bc338efc4eeed87d19c49dfaed38e036Chris Lattner } 324d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner return ReturnedValue; 325d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner} 3267152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner 327543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner/// CanTransformAccumulatorRecursion - If the specified instruction can be 328543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner/// transformed using accumulator recursion elimination, return the constant 329543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner/// which is the start of the accumulator value. Otherwise return null. 330543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner/// 331543d622ef7505910c1cdc09ada0ab797c3437590Chris LattnerValue *TailCallElim::CanTransformAccumulatorRecursion(Instruction *I, 332543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner CallInst *CI) { 33324080a98786cf393740cd035e27dd16c12827892Duncan Sands if (!I->isAssociative() || !I->isCommutative()) return 0; 334543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner assert(I->getNumOperands() == 2 && 33524080a98786cf393740cd035e27dd16c12827892Duncan Sands "Associative/commutative operations should have 2 args!"); 336543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner 337b5d84d13bc338efc4eeed87d19c49dfaed38e036Chris Lattner // Exactly one operand should be the result of the call instruction. 33807e6e56f57e8781a8d7bc601cc9034a3741d84c2Anton Korobeynikov if ((I->getOperand(0) == CI && I->getOperand(1) == CI) || 33907e6e56f57e8781a8d7bc601cc9034a3741d84c2Anton Korobeynikov (I->getOperand(0) != CI && I->getOperand(1) != CI)) 340543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner return 0; 341543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner 342543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // The only user of this instruction we allow is a single return instruction. 343543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner if (!I->hasOneUse() || !isa<ReturnInst>(I->use_back())) 344543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner return 0; 345543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner 346543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // Ok, now we have to check all of the other return instructions in this 347543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // function. If they return non-constants or differing values, then we cannot 348543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // transform the function safely. 349d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner return getCommonReturnValue(cast<ReturnInst>(I->use_back()), CI); 350543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner} 351543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner 352c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Chengstatic Instruction *FirstNonDbg(BasicBlock::iterator I) { 353c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng while (isa<DbgInfoIntrinsic>(I)) 354c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng ++I; 355c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng return &*I; 356c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng} 357c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng 358c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan ChengCallInst* 359c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan ChengTailCallElim::FindTRECandidate(Instruction *TI, 360c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng bool CannotTailCallElimCallsMarkedTail) { 361c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng BasicBlock *BB = TI->getParent(); 3627152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner Function *F = BB->getParent(); 3637152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner 364c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng if (&BB->front() == TI) // Make sure there is something before the terminator. 365c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng return 0; 3668d9455d4e4f63c368f17b74a36b472fc61685310Chris Lattner 3677152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner // Scan backwards from the return, checking to see if there is a tail call in 3687152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner // this block. If so, set CI to it. 369c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng CallInst *CI = 0; 370c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng BasicBlock::iterator BBI = TI; 371c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng while (true) { 3727152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner CI = dyn_cast<CallInst>(BBI); 3737152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner if (CI && CI->getCalledFunction() == F) 3747152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner break; 3757152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner 3767152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner if (BBI == BB->begin()) 377c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng return 0; // Didn't find a potential tail call. 3787152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner --BBI; 3797152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner } 3807152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner 381ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner // If this call is marked as a tail call, and if there are dynamic allocas in 382ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner // the function, we cannot perform this optimization. 383ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner if (CI->isTailCall() && CannotTailCallElimCallsMarkedTail) 384c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng return 0; 385ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner 386ea25b48af33be42e19236d8eac26bd42b45bcc1bDan Gohman // As a special case, detect code like this: 387ea25b48af33be42e19236d8eac26bd42b45bcc1bDan Gohman // double fabs(double f) { return __builtin_fabs(f); } // a 'fabs' call 388ea25b48af33be42e19236d8eac26bd42b45bcc1bDan Gohman // and disable this xform in this case, because the code generator will 389ea25b48af33be42e19236d8eac26bd42b45bcc1bDan Gohman // lower the call to fabs into inline code. 390ea25b48af33be42e19236d8eac26bd42b45bcc1bDan Gohman if (BB == &F->getEntryBlock() && 391c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng FirstNonDbg(BB->front()) == CI && 392c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng FirstNonDbg(llvm::next(BB->begin())) == TI && 393ea25b48af33be42e19236d8eac26bd42b45bcc1bDan Gohman callIsSmall(F)) { 394ea25b48af33be42e19236d8eac26bd42b45bcc1bDan Gohman // A single-block function with just a call and a return. Check that 395ea25b48af33be42e19236d8eac26bd42b45bcc1bDan Gohman // the arguments match. 396ea25b48af33be42e19236d8eac26bd42b45bcc1bDan Gohman CallSite::arg_iterator I = CallSite(CI).arg_begin(), 397ea25b48af33be42e19236d8eac26bd42b45bcc1bDan Gohman E = CallSite(CI).arg_end(); 398ea25b48af33be42e19236d8eac26bd42b45bcc1bDan Gohman Function::arg_iterator FI = F->arg_begin(), 399ea25b48af33be42e19236d8eac26bd42b45bcc1bDan Gohman FE = F->arg_end(); 400ea25b48af33be42e19236d8eac26bd42b45bcc1bDan Gohman for (; I != E && FI != FE; ++I, ++FI) 401ea25b48af33be42e19236d8eac26bd42b45bcc1bDan Gohman if (*I != &*FI) break; 402ea25b48af33be42e19236d8eac26bd42b45bcc1bDan Gohman if (I == E && FI == FE) 403c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng return 0; 404ea25b48af33be42e19236d8eac26bd42b45bcc1bDan Gohman } 405ea25b48af33be42e19236d8eac26bd42b45bcc1bDan Gohman 406c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng return CI; 407c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng} 408c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng 409c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Chengbool TailCallElim::EliminateRecursiveTailCall(CallInst *CI, ReturnInst *Ret, 410c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng BasicBlock *&OldEntry, 411c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng bool &TailCallsAreMarkedTail, 412c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng SmallVector<PHINode*, 8> &ArgumentPHIs, 413c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng bool CannotTailCallElimCallsMarkedTail) { 41424080a98786cf393740cd035e27dd16c12827892Duncan Sands // If we are introducing accumulator recursion to eliminate operations after 41524080a98786cf393740cd035e27dd16c12827892Duncan Sands // the call instruction that are both associative and commutative, the initial 41624080a98786cf393740cd035e27dd16c12827892Duncan Sands // value for the accumulator is placed in this variable. If this value is set 41724080a98786cf393740cd035e27dd16c12827892Duncan Sands // then we actually perform accumulator recursion elimination instead of 418d0d3ccc827de69de3d9f666aa922f5f191219a06Duncan Sands // simple tail recursion elimination. If the operation is an LLVM instruction 419d0d3ccc827de69de3d9f666aa922f5f191219a06Duncan Sands // (eg: "add") then it is recorded in AccumulatorRecursionInstr. If not, then 420d0d3ccc827de69de3d9f666aa922f5f191219a06Duncan Sands // we are handling the case when the return instruction returns a constant C 421d0d3ccc827de69de3d9f666aa922f5f191219a06Duncan Sands // which is different to the constant returned by other return instructions 422d0d3ccc827de69de3d9f666aa922f5f191219a06Duncan Sands // (which is recorded in AccumulatorRecursionEliminationInitVal). This is a 423d0d3ccc827de69de3d9f666aa922f5f191219a06Duncan Sands // special case of accumulator recursion, the operation being "return C". 424543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner Value *AccumulatorRecursionEliminationInitVal = 0; 425543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner Instruction *AccumulatorRecursionInstr = 0; 426543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner 4277152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner // Ok, we found a potential tail call. We can currently only transform the 4287152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner // tail call if all of the instructions between the call and the return are 4297152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner // movable to above the call itself, leaving the call next to the return. 4307152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner // Check that this is the case now. 431c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng BasicBlock::iterator BBI = CI; 432c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng for (++BBI; &*BBI != Ret; ++BBI) { 433b5d84d13bc338efc4eeed87d19c49dfaed38e036Chris Lattner if (CanMoveAboveCall(BBI, CI)) continue; 434b5d84d13bc338efc4eeed87d19c49dfaed38e036Chris Lattner 435b5d84d13bc338efc4eeed87d19c49dfaed38e036Chris Lattner // If we can't move the instruction above the call, it might be because it 436b5d84d13bc338efc4eeed87d19c49dfaed38e036Chris Lattner // is an associative and commutative operation that could be tranformed 437b5d84d13bc338efc4eeed87d19c49dfaed38e036Chris Lattner // using accumulator recursion elimination. Check to see if this is the 438b5d84d13bc338efc4eeed87d19c49dfaed38e036Chris Lattner // case, and if so, remember the initial accumulator value for later. 439b5d84d13bc338efc4eeed87d19c49dfaed38e036Chris Lattner if ((AccumulatorRecursionEliminationInitVal = 440b5d84d13bc338efc4eeed87d19c49dfaed38e036Chris Lattner CanTransformAccumulatorRecursion(BBI, CI))) { 441b5d84d13bc338efc4eeed87d19c49dfaed38e036Chris Lattner // Yes, this is accumulator recursion. Remember which instruction 442b5d84d13bc338efc4eeed87d19c49dfaed38e036Chris Lattner // accumulates. 443b5d84d13bc338efc4eeed87d19c49dfaed38e036Chris Lattner AccumulatorRecursionInstr = BBI; 444b5d84d13bc338efc4eeed87d19c49dfaed38e036Chris Lattner } else { 445b5d84d13bc338efc4eeed87d19c49dfaed38e036Chris Lattner return false; // Otherwise, we cannot eliminate the tail recursion! 446543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner } 447b5d84d13bc338efc4eeed87d19c49dfaed38e036Chris Lattner } 4487152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner 4497152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner // We can only transform call/return pairs that either ignore the return value 450d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner // of the call and return void, ignore the value of the call and return a 451d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner // constant, return the value returned by the tail call, or that are being 452d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner // accumulator recursion variable eliminated. 453826c49132a9cba1e08a5fce78d05561d9a3746ceDevang Patel if (Ret->getNumOperands() == 1 && Ret->getReturnValue() != CI && 4543b5f45042b17ad52815e3dd6c0c1df99f196dd04Chris Lattner !isa<UndefValue>(Ret->getReturnValue()) && 455d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner AccumulatorRecursionEliminationInitVal == 0 && 456d0d3ccc827de69de3d9f666aa922f5f191219a06Duncan Sands !getCommonReturnValue(0, CI)) { 457d0d3ccc827de69de3d9f666aa922f5f191219a06Duncan Sands // One case remains that we are able to handle: the current return 458d0d3ccc827de69de3d9f666aa922f5f191219a06Duncan Sands // instruction returns a constant, and all other return instructions 459d0d3ccc827de69de3d9f666aa922f5f191219a06Duncan Sands // return a different constant. 460d0d3ccc827de69de3d9f666aa922f5f191219a06Duncan Sands if (!isDynamicConstant(Ret->getReturnValue(), CI, Ret)) 461d0d3ccc827de69de3d9f666aa922f5f191219a06Duncan Sands return false; // Current return instruction does not return a constant. 462d0d3ccc827de69de3d9f666aa922f5f191219a06Duncan Sands // Check that all other return instructions return a common constant. If 463d0d3ccc827de69de3d9f666aa922f5f191219a06Duncan Sands // so, record it in AccumulatorRecursionEliminationInitVal. 464d0d3ccc827de69de3d9f666aa922f5f191219a06Duncan Sands AccumulatorRecursionEliminationInitVal = getCommonReturnValue(Ret, CI); 465d0d3ccc827de69de3d9f666aa922f5f191219a06Duncan Sands if (!AccumulatorRecursionEliminationInitVal) 466d0d3ccc827de69de3d9f666aa922f5f191219a06Duncan Sands return false; 467d0d3ccc827de69de3d9f666aa922f5f191219a06Duncan Sands } 4687152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner 469c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng BasicBlock *BB = Ret->getParent(); 470c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng Function *F = BB->getParent(); 471c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng 4727152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner // OK! We can transform this tail call. If this is the first one found, 4737152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner // create the new entry block, allowing us to branch back to the old entry. 4747152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner if (OldEntry == 0) { 4757152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner OldEntry = &F->getEntryBlock(); 4761d0be15f89cb5056e20e2d24faa8d6afb1573bcaOwen Anderson BasicBlock *NewEntry = BasicBlock::Create(F->getContext(), "", F, OldEntry); 4776934a04a8c15e9971cd1ea4d5c8df2d7afdd5be5Chris Lattner NewEntry->takeName(OldEntry); 4786934a04a8c15e9971cd1ea4d5c8df2d7afdd5be5Chris Lattner OldEntry->setName("tailrecurse"); 479051a950000e21935165db56695e35bade668193bGabor Greif BranchInst::Create(OldEntry, NewEntry); 480fd93908ae8b9684fe71c239e3c6cfe13ff6a2663Misha Brukman 481ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner // If this tail call is marked 'tail' and if there are any allocas in the 482ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner // entry block, move them up to the new entry block. 483ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner TailCallsAreMarkedTail = CI->isTailCall(); 484ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner if (TailCallsAreMarkedTail) 485ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner // Move all fixed sized allocas from OldEntry to NewEntry. 486ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner for (BasicBlock::iterator OEBI = OldEntry->begin(), E = OldEntry->end(), 487ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner NEBI = NewEntry->begin(); OEBI != E; ) 488ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner if (AllocaInst *AI = dyn_cast<AllocaInst>(OEBI++)) 489ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner if (isa<ConstantInt>(AI->getArraySize())) 4904bc5f8071a28b6fc4f4c2207dd03a5f747d0d84bChris Lattner AI->moveBefore(NEBI); 491ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner 4927152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner // Now that we have created a new block, which jumps to the entry 4937152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner // block, insert a PHI node for each argument of the function. 4947152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner // For now, we initialize each PHI to only have the real arguments 4957152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner // which are passed in. 4967152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner Instruction *InsertPos = OldEntry->begin(); 4977f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattner for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(); 4987f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattner I != E; ++I) { 499b1dbcd886a4b5597a839f299054b78b33fb2d6dfGabor Greif PHINode *PN = PHINode::Create(I->getType(), 500b1dbcd886a4b5597a839f299054b78b33fb2d6dfGabor Greif I->getName() + ".tr", InsertPos); 5017152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner I->replaceAllUsesWith(PN); // Everyone use the PHI node now! 5027152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner PN->addIncoming(I, NewEntry); 5037152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner ArgumentPHIs.push_back(PN); 5047152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner } 5057152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner } 506fd93908ae8b9684fe71c239e3c6cfe13ff6a2663Misha Brukman 507ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner // If this function has self recursive calls in the tail position where some 508ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner // are marked tail and some are not, only transform one flavor or another. We 509ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner // have to choose whether we move allocas in the entry block to the new entry 510ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner // block or not, so we can't make a good choice for both. NOTE: We could do 511ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner // slightly better here in the case that the function has no entry block 512ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner // allocas. 513ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner if (TailCallsAreMarkedTail && !CI->isTailCall()) 514ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner return false; 515ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner 5167152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner // Ok, now that we know we have a pseudo-entry block WITH all of the 5177152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner // required PHI nodes, add entries into the PHI node for the actual 5187152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner // parameters passed into the tail-recursive call. 519407014f9a5f05f5a5867e5992a036358acc4a441Gabor Greif for (unsigned i = 0, e = CI->getNumArgOperands(); i != e; ++i) 520de9f5452d3ae894bb7fdd455cec5af50e2560aa5Gabor Greif ArgumentPHIs[i]->addIncoming(CI->getArgOperand(i), BB); 521fd93908ae8b9684fe71c239e3c6cfe13ff6a2663Misha Brukman 522543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // If we are introducing an accumulator variable to eliminate the recursion, 523543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // do so now. Note that we _know_ that no subsequent tail recursion 524543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // eliminations will happen on this function because of the way the 525543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // accumulator recursion predicate is set up. 526543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // 527543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner if (AccumulatorRecursionEliminationInitVal) { 528543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner Instruction *AccRecInstr = AccumulatorRecursionInstr; 529543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // Start by inserting a new PHI node for the accumulator. 530d0d3ccc827de69de3d9f666aa922f5f191219a06Duncan Sands PHINode *AccPN = 531d0d3ccc827de69de3d9f666aa922f5f191219a06Duncan Sands PHINode::Create(AccumulatorRecursionEliminationInitVal->getType(), 532d0d3ccc827de69de3d9f666aa922f5f191219a06Duncan Sands "accumulator.tr", OldEntry->begin()); 533543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner 534543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // Loop over all of the predecessors of the tail recursion block. For the 535543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // real entry into the function we seed the PHI with the initial value, 536543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // computed earlier. For any other existing branches to this block (due to 537543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // other tail recursions eliminated) the accumulator is not modified. 538543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // Because we haven't added the branch in the current block to OldEntry yet, 539543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // it will not show up as a predecessor. 540543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner for (pred_iterator PI = pred_begin(OldEntry), PE = pred_end(OldEntry); 541543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner PI != PE; ++PI) { 542a8b9df7bd96e0b0bc6dec448d30b7d72180b6595Gabor Greif BasicBlock *P = *PI; 543a8b9df7bd96e0b0bc6dec448d30b7d72180b6595Gabor Greif if (P == &F->getEntryBlock()) 544a8b9df7bd96e0b0bc6dec448d30b7d72180b6595Gabor Greif AccPN->addIncoming(AccumulatorRecursionEliminationInitVal, P); 545543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner else 546a8b9df7bd96e0b0bc6dec448d30b7d72180b6595Gabor Greif AccPN->addIncoming(AccPN, P); 547543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner } 548543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner 549d0d3ccc827de69de3d9f666aa922f5f191219a06Duncan Sands if (AccRecInstr) { 550d0d3ccc827de69de3d9f666aa922f5f191219a06Duncan Sands // Add an incoming argument for the current block, which is computed by 551d0d3ccc827de69de3d9f666aa922f5f191219a06Duncan Sands // our associative and commutative accumulator instruction. 552d0d3ccc827de69de3d9f666aa922f5f191219a06Duncan Sands AccPN->addIncoming(AccRecInstr, BB); 553d0d3ccc827de69de3d9f666aa922f5f191219a06Duncan Sands 554d0d3ccc827de69de3d9f666aa922f5f191219a06Duncan Sands // Next, rewrite the accumulator recursion instruction so that it does not 555d0d3ccc827de69de3d9f666aa922f5f191219a06Duncan Sands // use the result of the call anymore, instead, use the PHI node we just 556d0d3ccc827de69de3d9f666aa922f5f191219a06Duncan Sands // inserted. 557d0d3ccc827de69de3d9f666aa922f5f191219a06Duncan Sands AccRecInstr->setOperand(AccRecInstr->getOperand(0) != CI, AccPN); 558d0d3ccc827de69de3d9f666aa922f5f191219a06Duncan Sands } else { 559d0d3ccc827de69de3d9f666aa922f5f191219a06Duncan Sands // Add an incoming argument for the current block, which is just the 560d0d3ccc827de69de3d9f666aa922f5f191219a06Duncan Sands // constant returned by the current return instruction. 561d0d3ccc827de69de3d9f666aa922f5f191219a06Duncan Sands AccPN->addIncoming(Ret->getReturnValue(), BB); 562d0d3ccc827de69de3d9f666aa922f5f191219a06Duncan Sands } 563543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner 564543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // Finally, rewrite any return instructions in the program to return the PHI 565543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // node instead of the "initval" that they do currently. This loop will 566543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // actually rewrite the return value we are destroying, but that's ok. 567543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner for (Function::iterator BBI = F->begin(), E = F->end(); BBI != E; ++BBI) 568543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner if (ReturnInst *RI = dyn_cast<ReturnInst>(BBI->getTerminator())) 569543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner RI->setOperand(0, AccPN); 570543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner ++NumAccumAdded; 571543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner } 572543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner 5737152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner // Now that all of the PHI nodes are in place, remove the call and 5747152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner // ret instructions, replacing them with an unconditional branch. 575051a950000e21935165db56695e35bade668193bGabor Greif BranchInst::Create(OldEntry, Ret); 5767152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner BB->getInstList().erase(Ret); // Remove return. 5777152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner BB->getInstList().erase(CI); // Remove call. 578543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner ++NumEliminated; 5797152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner return true; 5807152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner} 581c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng 582c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Chengbool TailCallElim::FoldReturnAndProcessPred(BasicBlock *BB, 583c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng ReturnInst *Ret, BasicBlock *&OldEntry, 584c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng bool &TailCallsAreMarkedTail, 585c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng SmallVector<PHINode*, 8> &ArgumentPHIs, 586c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng bool CannotTailCallElimCallsMarkedTail) { 587c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng bool Change = false; 588c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng 589c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng // If the return block contains nothing but the return and PHI's, 590c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng // there might be an opportunity to duplicate the return in its 591c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng // predecessors and perform TRC there. Look for predecessors that end 592c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng // in unconditional branch and recursive call(s). 593c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng SmallVector<BranchInst*, 8> UncondBranchPreds; 594c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) { 595c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng BasicBlock *Pred = *PI; 596c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng TerminatorInst *PTI = Pred->getTerminator(); 597c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng if (BranchInst *BI = dyn_cast<BranchInst>(PTI)) 598c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng if (BI->isUnconditional()) 599c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng UncondBranchPreds.push_back(BI); 600c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng } 601c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng 602c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng while (!UncondBranchPreds.empty()) { 603c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng BranchInst *BI = UncondBranchPreds.pop_back_val(); 604c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng BasicBlock *Pred = BI->getParent(); 605c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng if (CallInst *CI = FindTRECandidate(BI, CannotTailCallElimCallsMarkedTail)){ 606c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng DEBUG(dbgs() << "FOLDING: " << *BB 607c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng << "INTO UNCOND BRANCH PRED: " << *Pred); 608c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng EliminateRecursiveTailCall(CI, FoldReturnIntoUncondBranch(Ret, BB, Pred), 609c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng OldEntry, TailCallsAreMarkedTail, ArgumentPHIs, 610c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng CannotTailCallElimCallsMarkedTail); 61160f5ad46c2147af79035a43e5745e46376124780Evan Cheng ++NumRetDuped; 612c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng Change = true; 613c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng } 614c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng } 615c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng 616c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng return Change; 617c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng} 618c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng 619c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Chengbool TailCallElim::ProcessReturningBlock(ReturnInst *Ret, BasicBlock *&OldEntry, 620c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng bool &TailCallsAreMarkedTail, 621c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng SmallVector<PHINode*, 8> &ArgumentPHIs, 622c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng bool CannotTailCallElimCallsMarkedTail) { 623c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng CallInst *CI = FindTRECandidate(Ret, CannotTailCallElimCallsMarkedTail); 624c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng if (!CI) 625c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng return false; 626c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng 627c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng return EliminateRecursiveTailCall(CI, Ret, OldEntry, TailCallsAreMarkedTail, 628c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng ArgumentPHIs, 629c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng CannotTailCallElimCallsMarkedTail); 630c3f507f98a0747bd256e1c13536060b6fc5c4b62Evan Cheng} 631