TailRecursionElimination.cpp revision 6a35b40250735a50efe66c88414cdd3b79185019
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 19543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner// recursive by an associative expression to use an accumulator variable, 20543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner// thus compiling the typical naive factorial or 'fib' implementation into 21543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner// 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. 287f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattner// 4. If it can prove that callees do not access theier 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" 556a35b40250735a50efe66c88414cdd3b79185019Chris Lattner#include "llvm/Transforms/Utils/Local.h" 56ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner#include "llvm/Constants.h" 572240d2b3f7b9f5835868c83ce78d125d1b65212bChris Lattner#include "llvm/DerivedTypes.h" 582240d2b3f7b9f5835868c83ce78d125d1b65212bChris Lattner#include "llvm/Function.h" 592240d2b3f7b9f5835868c83ce78d125d1b65212bChris Lattner#include "llvm/Instructions.h" 602240d2b3f7b9f5835868c83ce78d125d1b65212bChris Lattner#include "llvm/Pass.h" 61543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner#include "llvm/Support/CFG.h" 62551ccae044b0ff658fe629dd67edd5ffe75d10e8Reid Spencer#include "llvm/ADT/Statistic.h" 639133fe28954d498fc4de13064c7d65bd811de02cReid Spencer#include "llvm/Support/Compiler.h" 64f8485c643412dbff46fe87ea2867445169a5c28eChris Lattnerusing namespace llvm; 65d0fde30ce850b78371fd1386338350591f9ff494Brian Gaeke 660e5f499638c8d277b9dc4a4385712177c53b5681Chris LattnerSTATISTIC(NumEliminated, "Number of tail calls removed"); 670e5f499638c8d277b9dc4a4385712177c53b5681Chris LattnerSTATISTIC(NumAccumAdded, "Number of accumulators introduced"); 682240d2b3f7b9f5835868c83ce78d125d1b65212bChris Lattner 690e5f499638c8d277b9dc4a4385712177c53b5681Chris Lattnernamespace { 709133fe28954d498fc4de13064c7d65bd811de02cReid Spencer struct VISIBILITY_HIDDEN TailCallElim : public FunctionPass { 71ecd94c804a563f2a86572dcf1d2e81f397e19daaNick Lewycky static char ID; // Pass identification, replacement for typeid 72ae73dc1448d25b02cabc7c64c86c64371453dda8Dan Gohman TailCallElim() : FunctionPass(&ID) {} 73794fd75c67a2cdc128d67342c6d88a504d186896Devang Patel 742240d2b3f7b9f5835868c83ce78d125d1b65212bChris Lattner virtual bool runOnFunction(Function &F); 757152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner 767152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner private: 777152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner bool ProcessReturningBlock(ReturnInst *RI, BasicBlock *&OldEntry, 78ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner bool &TailCallsAreMarkedTail, 79ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner std::vector<PHINode*> &ArgumentPHIs, 80ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner bool CannotTailCallElimCallsMarkedTail); 817152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner bool CanMoveAboveCall(Instruction *I, CallInst *CI); 82543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner Value *CanTransformAccumulatorRecursion(Instruction *I, CallInst *CI); 832240d2b3f7b9f5835868c83ce78d125d1b65212bChris Lattner }; 842240d2b3f7b9f5835868c83ce78d125d1b65212bChris Lattner} 852240d2b3f7b9f5835868c83ce78d125d1b65212bChris Lattner 86844731a7f1909f55935e3514c9e713a62d67662eDan Gohmanchar TailCallElim::ID = 0; 87844731a7f1909f55935e3514c9e713a62d67662eDan Gohmanstatic RegisterPass<TailCallElim> X("tailcallelim", "Tail Call Elimination"); 88844731a7f1909f55935e3514c9e713a62d67662eDan Gohman 89d0fde30ce850b78371fd1386338350591f9ff494Brian Gaeke// Public interface to the TailCallElimination pass 90f8485c643412dbff46fe87ea2867445169a5c28eChris LattnerFunctionPass *llvm::createTailCallEliminationPass() { 91f8485c643412dbff46fe87ea2867445169a5c28eChris Lattner return new TailCallElim(); 92f8485c643412dbff46fe87ea2867445169a5c28eChris Lattner} 933fc6ef1bb96d9a3194cef667a2d3cbc94e3fb189Chris Lattner 942240d2b3f7b9f5835868c83ce78d125d1b65212bChris Lattner 957f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattner/// AllocaMightEscapeToCalls - Return true if this alloca may be accessed by 967f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattner/// callees of this function. We only do very simple analysis right now, this 977f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattner/// could be expanded in the future to use mod/ref information for particular 987f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattner/// call sites if desired. 997f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattnerstatic bool AllocaMightEscapeToCalls(AllocaInst *AI) { 1007f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattner // FIXME: do simple 'address taken' analysis. 1017f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattner return true; 1027f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattner} 1037f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattner 1047f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattner/// FunctionContainsAllocas - Scan the specified basic block for alloca 1057f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattner/// instructions. If it contains any that might be accessed by calls, return 1067f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattner/// true. 107ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattnerstatic bool CheckForEscapingAllocas(BasicBlock *BB, 108ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner bool &CannotTCETailMarkedCall) { 109ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner bool RetVal = false; 1107f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattner for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) 111ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner if (AllocaInst *AI = dyn_cast<AllocaInst>(I)) { 112ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner RetVal |= AllocaMightEscapeToCalls(AI); 113ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner 114ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner // If this alloca is in the body of the function, or if it is a variable 115ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner // sized allocation, we cannot tail call eliminate calls marked 'tail' 116ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner // with this mechanism. 117ecb7a77885b174cf4d001a9b48533b3979e7810dDan Gohman if (BB != &BB->getParent()->getEntryBlock() || 118ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner !isa<ConstantInt>(AI->getArraySize())) 119ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner CannotTCETailMarkedCall = true; 120ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner } 121ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner return RetVal; 1227f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattner} 1237f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattner 1242240d2b3f7b9f5835868c83ce78d125d1b65212bChris Lattnerbool TailCallElim::runOnFunction(Function &F) { 1252240d2b3f7b9f5835868c83ce78d125d1b65212bChris Lattner // If this function is a varargs function, we won't be able to PHI the args 1262240d2b3f7b9f5835868c83ce78d125d1b65212bChris Lattner // right, so don't even try to convert it... 1272240d2b3f7b9f5835868c83ce78d125d1b65212bChris Lattner if (F.getFunctionType()->isVarArg()) return false; 1282240d2b3f7b9f5835868c83ce78d125d1b65212bChris Lattner 1292240d2b3f7b9f5835868c83ce78d125d1b65212bChris Lattner BasicBlock *OldEntry = 0; 130ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner bool TailCallsAreMarkedTail = false; 1312240d2b3f7b9f5835868c83ce78d125d1b65212bChris Lattner std::vector<PHINode*> ArgumentPHIs; 1322240d2b3f7b9f5835868c83ce78d125d1b65212bChris Lattner bool MadeChange = false; 1332240d2b3f7b9f5835868c83ce78d125d1b65212bChris Lattner 1347f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattner bool FunctionContainsEscapingAllocas = false; 1357f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattner 136ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner // CannotTCETailMarkedCall - If true, we cannot perform TCE on tail calls 137ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner // marked with the 'tail' attribute, because doing so would cause the stack 138ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner // size to increase (real TCE would deallocate variable sized allocas, TCE 139ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner // doesn't). 140ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner bool CannotTCETailMarkedCall = false; 141ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner 1427f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattner // Loop over the function, looking for any returning blocks, and keeping track 1437f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattner // of whether this function has any non-trivially used allocas. 1447f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattner for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) { 145ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner if (FunctionContainsEscapingAllocas && CannotTCETailMarkedCall) 146ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner break; 14700b16889ab461b7ecef1c91ade101186b7f1fce2Jeff Cohen 1484c0e4cdc40bbf94766242294fe386f4eb2d32d2eChris Lattner FunctionContainsEscapingAllocas |= 149ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner CheckForEscapingAllocas(BB, CannotTCETailMarkedCall); 1507f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattner } 15132b1e87f111d79f3f5b0e86c8f138c02bef8aa18Chris Lattner 15232b1e87f111d79f3f5b0e86c8f138c02bef8aa18Chris Lattner /// FIXME: The code generator produces really bad code when an 'escaping 15332b1e87f111d79f3f5b0e86c8f138c02bef8aa18Chris Lattner /// alloca' is changed from being a static alloca to being a dynamic alloca. 15432b1e87f111d79f3f5b0e86c8f138c02bef8aa18Chris Lattner /// Until this is resolved, disable this transformation if that would ever 15532b1e87f111d79f3f5b0e86c8f138c02bef8aa18Chris Lattner /// happen. This bug is PR962. 15632b1e87f111d79f3f5b0e86c8f138c02bef8aa18Chris Lattner if (FunctionContainsEscapingAllocas) 15732b1e87f111d79f3f5b0e86c8f138c02bef8aa18Chris Lattner return false; 15832b1e87f111d79f3f5b0e86c8f138c02bef8aa18Chris Lattner 159fd93908ae8b9684fe71c239e3c6cfe13ff6a2663Misha Brukman 160ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner // Second pass, change any tail calls to loops. 161ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) 162ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner if (ReturnInst *Ret = dyn_cast<ReturnInst>(BB->getTerminator())) 163ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner MadeChange |= ProcessReturningBlock(Ret, OldEntry, TailCallsAreMarkedTail, 164ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner ArgumentPHIs,CannotTCETailMarkedCall); 165ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner 166cf2f89251d45bc9783917874adb9029f71d50068Chris Lattner // If we eliminated any tail recursions, it's possible that we inserted some 167cf2f89251d45bc9783917874adb9029f71d50068Chris Lattner // silly PHI nodes which just merge an initial value (the incoming operand) 168cf2f89251d45bc9783917874adb9029f71d50068Chris Lattner // with themselves. Check to see if we did and clean up our mess if so. This 169cf2f89251d45bc9783917874adb9029f71d50068Chris Lattner // occurs when a function passes an argument straight through to its tail 170cf2f89251d45bc9783917874adb9029f71d50068Chris Lattner // call. 171cf2f89251d45bc9783917874adb9029f71d50068Chris Lattner if (!ArgumentPHIs.empty()) { 172cf2f89251d45bc9783917874adb9029f71d50068Chris Lattner for (unsigned i = 0, e = ArgumentPHIs.size(); i != e; ++i) { 173cf2f89251d45bc9783917874adb9029f71d50068Chris Lattner PHINode *PN = ArgumentPHIs[i]; 174cf2f89251d45bc9783917874adb9029f71d50068Chris Lattner 175cf2f89251d45bc9783917874adb9029f71d50068Chris Lattner // If the PHI Node is a dynamic constant, replace it with the value it is. 176ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner if (Value *PNV = PN->hasConstantValue()) { 177ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner PN->replaceAllUsesWith(PNV); 178ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner PN->eraseFromParent(); 179cf2f89251d45bc9783917874adb9029f71d50068Chris Lattner } 180cf2f89251d45bc9783917874adb9029f71d50068Chris Lattner } 181cf2f89251d45bc9783917874adb9029f71d50068Chris Lattner } 182cf2f89251d45bc9783917874adb9029f71d50068Chris Lattner 1837f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattner // Finally, if this function contains no non-escaping allocas, mark all calls 1847f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattner // in the function as eligible for tail calls (there is no stack memory for 1857f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattner // them to access). 1867f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattner if (!FunctionContainsEscapingAllocas) 1877f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattner for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) 1887f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattner for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) 189c5dc660ea0b153904de601eadd40fa4962c8c71cChris Lattner if (CallInst *CI = dyn_cast<CallInst>(I)) { 1907f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattner CI->setTailCall(); 191c5dc660ea0b153904de601eadd40fa4962c8c71cChris Lattner MadeChange = true; 192c5dc660ea0b153904de601eadd40fa4962c8c71cChris Lattner } 1937f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattner 1942240d2b3f7b9f5835868c83ce78d125d1b65212bChris Lattner return MadeChange; 1952240d2b3f7b9f5835868c83ce78d125d1b65212bChris Lattner} 1967152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner 1977152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner 198543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner/// CanMoveAboveCall - Return true if it is safe to move the specified 199543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner/// instruction from after the call to before the call, assuming that all 200543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner/// instructions between the call and this instruction are movable. 201543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner/// 2027152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattnerbool TailCallElim::CanMoveAboveCall(Instruction *I, CallInst *CI) { 2037152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner // FIXME: We can move load/store/call/free instructions above the call if the 2047152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner // call does not mod/ref the memory location being processed. 2056a35b40250735a50efe66c88414cdd3b79185019Chris Lattner if (I->mayHaveSideEffects()) // This also handles volatile loads. 2067152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner return false; 2076a35b40250735a50efe66c88414cdd3b79185019Chris Lattner 2086a35b40250735a50efe66c88414cdd3b79185019Chris Lattner if (LoadInst* L = dyn_cast<LoadInst>(I)) { 2096a35b40250735a50efe66c88414cdd3b79185019Chris Lattner // Loads may always be moved above calls without side effects. 2106a35b40250735a50efe66c88414cdd3b79185019Chris Lattner if (CI->mayHaveSideEffects()) { 2116a35b40250735a50efe66c88414cdd3b79185019Chris Lattner // Non-volatile loads may be moved above a call with side effects if it 2126a35b40250735a50efe66c88414cdd3b79185019Chris Lattner // does not write to memory and the load provably won't trap. 2136a35b40250735a50efe66c88414cdd3b79185019Chris Lattner // FIXME: Writes to memory only matter if they may alias the pointer 2146a35b40250735a50efe66c88414cdd3b79185019Chris Lattner // being loaded from. 2156a35b40250735a50efe66c88414cdd3b79185019Chris Lattner if (CI->mayWriteToMemory() || 2166a35b40250735a50efe66c88414cdd3b79185019Chris Lattner !isSafeToLoadUnconditionally(L->getPointerOperand(), L)) 2176a35b40250735a50efe66c88414cdd3b79185019Chris Lattner return false; 2186a35b40250735a50efe66c88414cdd3b79185019Chris Lattner } 2196a35b40250735a50efe66c88414cdd3b79185019Chris Lattner } 2207152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner 2217152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner // Otherwise, if this is a side-effect free instruction, check to make sure 2227152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner // that it does not use the return value of the call. If it doesn't use the 2237152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner // return value of the call, it must only use things that are defined before 2247152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner // the call, or movable instructions between the call and the instruction 2257152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner // itself. 2267152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) 2277152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner if (I->getOperand(i) == CI) 2287152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner return false; 2297152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner return true; 2307152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner} 2317152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner 232d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner// isDynamicConstant - Return true if the specified value is the same when the 233d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner// return would exit as it was when the initial iteration of the recursive 234d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner// function was executed. 235d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner// 236d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner// We currently handle static constants and arguments that are not modified as 237d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner// part of the recursion. 238d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner// 239d64152a70842b2f4186aa912938e69ca09c1434cChris Lattnerstatic bool isDynamicConstant(Value *V, CallInst *CI) { 240d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner if (isa<Constant>(V)) return true; // Static constants are always dyn consts 241d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner 242d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner // Check to see if this is an immutable argument, if so, the value 243d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner // will be available to initialize the accumulator. 244d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner if (Argument *Arg = dyn_cast<Argument>(V)) { 245d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner // Figure out which argument number this is... 246d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner unsigned ArgNo = 0; 247d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner Function *F = CI->getParent()->getParent(); 248e4d5c441e04bdc00ccf1804744af670655123b07Chris Lattner for (Function::arg_iterator AI = F->arg_begin(); &*AI != Arg; ++AI) 249d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner ++ArgNo; 250fd93908ae8b9684fe71c239e3c6cfe13ff6a2663Misha Brukman 251d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner // If we are passing this argument into call as the corresponding 252d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner // argument operand, then the argument is dynamically constant. 253d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner // Otherwise, we cannot transform this function safely. 254d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner if (CI->getOperand(ArgNo+1) == Arg) 255d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner return true; 256d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner } 257d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner // Not a constant or immutable argument, we can't safely transform. 258d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner return false; 259d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner} 260d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner 261d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner// getCommonReturnValue - Check to see if the function containing the specified 262d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner// return instruction and tail call consistently returns the same 263d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner// runtime-constant value at all exit points. If so, return the returned value. 264d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner// 265d64152a70842b2f4186aa912938e69ca09c1434cChris Lattnerstatic Value *getCommonReturnValue(ReturnInst *TheRI, CallInst *CI) { 266d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner Function *F = TheRI->getParent()->getParent(); 267d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner Value *ReturnedValue = 0; 268d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner 269826c49132a9cba1e08a5fce78d05561d9a3746ceDevang Patel // TODO: Handle multiple value ret instructions; 270826c49132a9cba1e08a5fce78d05561d9a3746ceDevang Patel if (isa<StructType>(F->getReturnType())) 271826c49132a9cba1e08a5fce78d05561d9a3746ceDevang Patel return 0; 272826c49132a9cba1e08a5fce78d05561d9a3746ceDevang Patel 273d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner for (Function::iterator BBI = F->begin(), E = F->end(); BBI != E; ++BBI) 274d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner if (ReturnInst *RI = dyn_cast<ReturnInst>(BBI->getTerminator())) 275d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner if (RI != TheRI) { 276d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner Value *RetOp = RI->getOperand(0); 277d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner 278d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner // We can only perform this transformation if the value returned is 279d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner // evaluatable at the start of the initial invocation of the function, 280d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner // instead of at the end of the evaluation. 281d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner // 282d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner if (!isDynamicConstant(RetOp, CI)) 283d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner return 0; 284d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner 285d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner if (ReturnedValue && RetOp != ReturnedValue) 286d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner return 0; // Cannot transform if differing values are returned. 287d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner ReturnedValue = RetOp; 288d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner } 289d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner return ReturnedValue; 290d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner} 2917152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner 292543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner/// CanTransformAccumulatorRecursion - If the specified instruction can be 293543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner/// transformed using accumulator recursion elimination, return the constant 294543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner/// which is the start of the accumulator value. Otherwise return null. 295543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner/// 296543d622ef7505910c1cdc09ada0ab797c3437590Chris LattnerValue *TailCallElim::CanTransformAccumulatorRecursion(Instruction *I, 297543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner CallInst *CI) { 298543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner if (!I->isAssociative()) return 0; 299543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner assert(I->getNumOperands() == 2 && 300543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner "Associative operations should have 2 args!"); 301543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner 302543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // Exactly one operand should be the result of the call instruction... 30307e6e56f57e8781a8d7bc601cc9034a3741d84c2Anton Korobeynikov if ((I->getOperand(0) == CI && I->getOperand(1) == CI) || 30407e6e56f57e8781a8d7bc601cc9034a3741d84c2Anton Korobeynikov (I->getOperand(0) != CI && I->getOperand(1) != CI)) 305543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner return 0; 306543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner 307543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // The only user of this instruction we allow is a single return instruction. 308543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner if (!I->hasOneUse() || !isa<ReturnInst>(I->use_back())) 309543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner return 0; 310543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner 311543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // Ok, now we have to check all of the other return instructions in this 312543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // function. If they return non-constants or differing values, then we cannot 313543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // transform the function safely. 314d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner return getCommonReturnValue(cast<ReturnInst>(I->use_back()), CI); 315543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner} 316543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner 3177152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattnerbool TailCallElim::ProcessReturningBlock(ReturnInst *Ret, BasicBlock *&OldEntry, 318ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner bool &TailCallsAreMarkedTail, 319ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner std::vector<PHINode*> &ArgumentPHIs, 320ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner bool CannotTailCallElimCallsMarkedTail) { 3217152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner BasicBlock *BB = Ret->getParent(); 3227152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner Function *F = BB->getParent(); 3237152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner 3247152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner if (&BB->front() == Ret) // Make sure there is something before the ret... 3257152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner return false; 3268d9455d4e4f63c368f17b74a36b472fc61685310Chris Lattner 3278d9455d4e4f63c368f17b74a36b472fc61685310Chris Lattner // If the return is in the entry block, then making this transformation would 3288d9455d4e4f63c368f17b74a36b472fc61685310Chris Lattner // turn infinite recursion into an infinite loop. This transformation is ok 3298d9455d4e4f63c368f17b74a36b472fc61685310Chris Lattner // in theory, but breaks some code like: 3308d9455d4e4f63c368f17b74a36b472fc61685310Chris Lattner // double fabs(double f) { return __builtin_fabs(f); } // a 'fabs' call 3318d9455d4e4f63c368f17b74a36b472fc61685310Chris Lattner // disable this xform in this case, because the code generator will lower the 3328d9455d4e4f63c368f17b74a36b472fc61685310Chris Lattner // call to fabs into inline code. 3338d9455d4e4f63c368f17b74a36b472fc61685310Chris Lattner if (BB == &F->getEntryBlock()) 3348d9455d4e4f63c368f17b74a36b472fc61685310Chris Lattner return false; 3357152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner 3367152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner // Scan backwards from the return, checking to see if there is a tail call in 3377152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner // this block. If so, set CI to it. 3387152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner CallInst *CI; 3397152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner BasicBlock::iterator BBI = Ret; 3407152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner while (1) { 3417152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner CI = dyn_cast<CallInst>(BBI); 3427152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner if (CI && CI->getCalledFunction() == F) 3437152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner break; 3447152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner 3457152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner if (BBI == BB->begin()) 3467152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner return false; // Didn't find a potential tail call. 3477152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner --BBI; 3487152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner } 3497152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner 350ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner // If this call is marked as a tail call, and if there are dynamic allocas in 351ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner // the function, we cannot perform this optimization. 352ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner if (CI->isTailCall() && CannotTailCallElimCallsMarkedTail) 353ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner return false; 354ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner 355543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // If we are introducing accumulator recursion to eliminate associative 356543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // operations after the call instruction, this variable contains the initial 357543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // value for the accumulator. If this value is set, we actually perform 358543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // accumulator recursion elimination instead of simple tail recursion 359543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // elimination. 360543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner Value *AccumulatorRecursionEliminationInitVal = 0; 361543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner Instruction *AccumulatorRecursionInstr = 0; 362543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner 3637152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner // Ok, we found a potential tail call. We can currently only transform the 3647152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner // tail call if all of the instructions between the call and the return are 3657152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner // movable to above the call itself, leaving the call next to the return. 3667152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner // Check that this is the case now. 3677152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner for (BBI = CI, ++BBI; &*BBI != Ret; ++BBI) 368543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner if (!CanMoveAboveCall(BBI, CI)) { 369543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // If we can't move the instruction above the call, it might be because it 370543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // is an associative operation that could be tranformed using accumulator 371543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // recursion elimination. Check to see if this is the case, and if so, 372543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // remember the initial accumulator value for later. 373543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner if ((AccumulatorRecursionEliminationInitVal = 374543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner CanTransformAccumulatorRecursion(BBI, CI))) { 375543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // Yes, this is accumulator recursion. Remember which instruction 376543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // accumulates. 377543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner AccumulatorRecursionInstr = BBI; 378543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner } else { 379543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner return false; // Otherwise, we cannot eliminate the tail recursion! 380543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner } 381543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner } 3827152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner 3837152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner // We can only transform call/return pairs that either ignore the return value 384d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner // of the call and return void, ignore the value of the call and return a 385d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner // constant, return the value returned by the tail call, or that are being 386d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner // accumulator recursion variable eliminated. 387826c49132a9cba1e08a5fce78d05561d9a3746ceDevang Patel if (Ret->getNumOperands() == 1 && Ret->getReturnValue() != CI && 3883b5f45042b17ad52815e3dd6c0c1df99f196dd04Chris Lattner !isa<UndefValue>(Ret->getReturnValue()) && 389d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner AccumulatorRecursionEliminationInitVal == 0 && 390d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner !getCommonReturnValue(Ret, CI)) 3917152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner return false; 3927152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner 3937152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner // OK! We can transform this tail call. If this is the first one found, 3947152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner // create the new entry block, allowing us to branch back to the old entry. 3957152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner if (OldEntry == 0) { 3967152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner OldEntry = &F->getEntryBlock(); 397051a950000e21935165db56695e35bade668193bGabor Greif BasicBlock *NewEntry = BasicBlock::Create("", F, OldEntry); 3986934a04a8c15e9971cd1ea4d5c8df2d7afdd5be5Chris Lattner NewEntry->takeName(OldEntry); 3996934a04a8c15e9971cd1ea4d5c8df2d7afdd5be5Chris Lattner OldEntry->setName("tailrecurse"); 400051a950000e21935165db56695e35bade668193bGabor Greif BranchInst::Create(OldEntry, NewEntry); 401fd93908ae8b9684fe71c239e3c6cfe13ff6a2663Misha Brukman 402ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner // If this tail call is marked 'tail' and if there are any allocas in the 403ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner // entry block, move them up to the new entry block. 404ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner TailCallsAreMarkedTail = CI->isTailCall(); 405ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner if (TailCallsAreMarkedTail) 406ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner // Move all fixed sized allocas from OldEntry to NewEntry. 407ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner for (BasicBlock::iterator OEBI = OldEntry->begin(), E = OldEntry->end(), 408ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner NEBI = NewEntry->begin(); OEBI != E; ) 409ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner if (AllocaInst *AI = dyn_cast<AllocaInst>(OEBI++)) 410ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner if (isa<ConstantInt>(AI->getArraySize())) 4114bc5f8071a28b6fc4f4c2207dd03a5f747d0d84bChris Lattner AI->moveBefore(NEBI); 412ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner 4137152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner // Now that we have created a new block, which jumps to the entry 4147152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner // block, insert a PHI node for each argument of the function. 4157152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner // For now, we initialize each PHI to only have the real arguments 4167152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner // which are passed in. 4177152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner Instruction *InsertPos = OldEntry->begin(); 4187f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattner for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(); 4197f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattner I != E; ++I) { 420b1dbcd886a4b5597a839f299054b78b33fb2d6dfGabor Greif PHINode *PN = PHINode::Create(I->getType(), 421b1dbcd886a4b5597a839f299054b78b33fb2d6dfGabor Greif I->getName() + ".tr", InsertPos); 4227152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner I->replaceAllUsesWith(PN); // Everyone use the PHI node now! 4237152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner PN->addIncoming(I, NewEntry); 4247152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner ArgumentPHIs.push_back(PN); 4257152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner } 4267152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner } 427fd93908ae8b9684fe71c239e3c6cfe13ff6a2663Misha Brukman 428ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner // If this function has self recursive calls in the tail position where some 429ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner // are marked tail and some are not, only transform one flavor or another. We 430ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner // have to choose whether we move allocas in the entry block to the new entry 431ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner // block or not, so we can't make a good choice for both. NOTE: We could do 432ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner // slightly better here in the case that the function has no entry block 433ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner // allocas. 434ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner if (TailCallsAreMarkedTail && !CI->isTailCall()) 435ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner return false; 436ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner 4377152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner // Ok, now that we know we have a pseudo-entry block WITH all of the 4387152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner // required PHI nodes, add entries into the PHI node for the actual 4397152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner // parameters passed into the tail-recursive call. 4407152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner for (unsigned i = 0, e = CI->getNumOperands()-1; i != e; ++i) 4417152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner ArgumentPHIs[i]->addIncoming(CI->getOperand(i+1), BB); 442fd93908ae8b9684fe71c239e3c6cfe13ff6a2663Misha Brukman 443543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // If we are introducing an accumulator variable to eliminate the recursion, 444543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // do so now. Note that we _know_ that no subsequent tail recursion 445543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // eliminations will happen on this function because of the way the 446543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // accumulator recursion predicate is set up. 447543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // 448543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner if (AccumulatorRecursionEliminationInitVal) { 449543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner Instruction *AccRecInstr = AccumulatorRecursionInstr; 450543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // Start by inserting a new PHI node for the accumulator. 451051a950000e21935165db56695e35bade668193bGabor Greif PHINode *AccPN = PHINode::Create(AccRecInstr->getType(), "accumulator.tr", 452051a950000e21935165db56695e35bade668193bGabor Greif OldEntry->begin()); 453543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner 454543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // Loop over all of the predecessors of the tail recursion block. For the 455543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // real entry into the function we seed the PHI with the initial value, 456543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // computed earlier. For any other existing branches to this block (due to 457543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // other tail recursions eliminated) the accumulator is not modified. 458543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // Because we haven't added the branch in the current block to OldEntry yet, 459543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // it will not show up as a predecessor. 460543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner for (pred_iterator PI = pred_begin(OldEntry), PE = pred_end(OldEntry); 461543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner PI != PE; ++PI) { 462543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner if (*PI == &F->getEntryBlock()) 463543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner AccPN->addIncoming(AccumulatorRecursionEliminationInitVal, *PI); 464543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner else 465543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner AccPN->addIncoming(AccPN, *PI); 466543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner } 467543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner 468543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // Add an incoming argument for the current block, which is computed by our 469543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // associative accumulator instruction. 470543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner AccPN->addIncoming(AccRecInstr, BB); 471543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner 472543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // Next, rewrite the accumulator recursion instruction so that it does not 473543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // use the result of the call anymore, instead, use the PHI node we just 474543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // inserted. 475543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner AccRecInstr->setOperand(AccRecInstr->getOperand(0) != CI, AccPN); 476543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner 477543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // Finally, rewrite any return instructions in the program to return the PHI 478543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // node instead of the "initval" that they do currently. This loop will 479543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // actually rewrite the return value we are destroying, but that's ok. 480543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner for (Function::iterator BBI = F->begin(), E = F->end(); BBI != E; ++BBI) 481543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner if (ReturnInst *RI = dyn_cast<ReturnInst>(BBI->getTerminator())) 482543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner RI->setOperand(0, AccPN); 483543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner ++NumAccumAdded; 484543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner } 485543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner 4867152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner // Now that all of the PHI nodes are in place, remove the call and 4877152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner // ret instructions, replacing them with an unconditional branch. 488051a950000e21935165db56695e35bade668193bGabor Greif BranchInst::Create(OldEntry, Ret); 4897152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner BB->getInstList().erase(Ret); // Remove return. 4907152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner BB->getInstList().erase(CI); // Remove call. 491543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner ++NumEliminated; 4927152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner return true; 4937152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner} 494