TailRecursionElimination.cpp revision 8d9455d4e4f63c368f17b74a36b472fc61685310
12240d2b3f7b9f5835868c83ce78d125d1b65212bChris Lattner//===- TailRecursionElimination.cpp - Eliminate Tail Calls ----------------===// 2fd93908ae8b9684fe71c239e3c6cfe13ff6a2663Misha Brukman// 3b576c94c15af9a440f69d9d03c2afead7971118cJohn Criswell// The LLVM Compiler Infrastructure 4b576c94c15af9a440f69d9d03c2afead7971118cJohn Criswell// 5b576c94c15af9a440f69d9d03c2afead7971118cJohn Criswell// This file was developed by the LLVM research group and is distributed under 6b576c94c15af9a440f69d9d03c2afead7971118cJohn Criswell// the University of Illinois Open Source 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" 55ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner#include "llvm/Constants.h" 562240d2b3f7b9f5835868c83ce78d125d1b65212bChris Lattner#include "llvm/DerivedTypes.h" 572240d2b3f7b9f5835868c83ce78d125d1b65212bChris Lattner#include "llvm/Function.h" 582240d2b3f7b9f5835868c83ce78d125d1b65212bChris Lattner#include "llvm/Instructions.h" 592240d2b3f7b9f5835868c83ce78d125d1b65212bChris Lattner#include "llvm/Pass.h" 60543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner#include "llvm/Support/CFG.h" 61551ccae044b0ff658fe629dd67edd5ffe75d10e8Reid Spencer#include "llvm/ADT/Statistic.h" 629133fe28954d498fc4de13064c7d65bd811de02cReid Spencer#include "llvm/Support/Compiler.h" 63f8485c643412dbff46fe87ea2867445169a5c28eChris Lattnerusing namespace llvm; 64d0fde30ce850b78371fd1386338350591f9ff494Brian Gaeke 650e5f499638c8d277b9dc4a4385712177c53b5681Chris LattnerSTATISTIC(NumEliminated, "Number of tail calls removed"); 660e5f499638c8d277b9dc4a4385712177c53b5681Chris LattnerSTATISTIC(NumAccumAdded, "Number of accumulators introduced"); 672240d2b3f7b9f5835868c83ce78d125d1b65212bChris Lattner 680e5f499638c8d277b9dc4a4385712177c53b5681Chris Lattnernamespace { 699133fe28954d498fc4de13064c7d65bd811de02cReid Spencer struct VISIBILITY_HIDDEN TailCallElim : public FunctionPass { 70ecd94c804a563f2a86572dcf1d2e81f397e19daaNick Lewycky static char ID; // Pass identification, replacement for typeid 71794fd75c67a2cdc128d67342c6d88a504d186896Devang Patel TailCallElim() : FunctionPass((intptr_t)&ID) {} 72794fd75c67a2cdc128d67342c6d88a504d186896Devang Patel 732240d2b3f7b9f5835868c83ce78d125d1b65212bChris Lattner virtual bool runOnFunction(Function &F); 747152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner 757152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner private: 767152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner bool ProcessReturningBlock(ReturnInst *RI, BasicBlock *&OldEntry, 77ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner bool &TailCallsAreMarkedTail, 78ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner std::vector<PHINode*> &ArgumentPHIs, 79ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner bool CannotTailCallElimCallsMarkedTail); 807152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner bool CanMoveAboveCall(Instruction *I, CallInst *CI); 81543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner Value *CanTransformAccumulatorRecursion(Instruction *I, CallInst *CI); 822240d2b3f7b9f5835868c83ce78d125d1b65212bChris Lattner }; 831997473cf72957d0e70322e2fe6fe2ab141c58a6Devang Patel char TailCallElim::ID = 0; 847f8897f22e88271cfa114998a4d6088e7c8e8e11Chris Lattner RegisterPass<TailCallElim> X("tailcallelim", "Tail Call Elimination"); 852240d2b3f7b9f5835868c83ce78d125d1b65212bChris Lattner} 862240d2b3f7b9f5835868c83ce78d125d1b65212bChris Lattner 87d0fde30ce850b78371fd1386338350591f9ff494Brian Gaeke// Public interface to the TailCallElimination pass 88f8485c643412dbff46fe87ea2867445169a5c28eChris LattnerFunctionPass *llvm::createTailCallEliminationPass() { 89f8485c643412dbff46fe87ea2867445169a5c28eChris Lattner return new TailCallElim(); 90f8485c643412dbff46fe87ea2867445169a5c28eChris Lattner} 913fc6ef1bb96d9a3194cef667a2d3cbc94e3fb189Chris Lattner 922240d2b3f7b9f5835868c83ce78d125d1b65212bChris Lattner 937f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattner/// AllocaMightEscapeToCalls - Return true if this alloca may be accessed by 947f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattner/// callees of this function. We only do very simple analysis right now, this 957f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattner/// could be expanded in the future to use mod/ref information for particular 967f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattner/// call sites if desired. 977f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattnerstatic bool AllocaMightEscapeToCalls(AllocaInst *AI) { 987f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattner // FIXME: do simple 'address taken' analysis. 997f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattner return true; 1007f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattner} 1017f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattner 1027f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattner/// FunctionContainsAllocas - Scan the specified basic block for alloca 1037f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattner/// instructions. If it contains any that might be accessed by calls, return 1047f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattner/// true. 105ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattnerstatic bool CheckForEscapingAllocas(BasicBlock *BB, 106ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner bool &CannotTCETailMarkedCall) { 107ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner bool RetVal = false; 1087f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattner for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) 109ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner if (AllocaInst *AI = dyn_cast<AllocaInst>(I)) { 110ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner RetVal |= AllocaMightEscapeToCalls(AI); 111ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner 112ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner // If this alloca is in the body of the function, or if it is a variable 113ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner // sized allocation, we cannot tail call eliminate calls marked 'tail' 114ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner // with this mechanism. 115ecb7a77885b174cf4d001a9b48533b3979e7810dDan Gohman if (BB != &BB->getParent()->getEntryBlock() || 116ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner !isa<ConstantInt>(AI->getArraySize())) 117ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner CannotTCETailMarkedCall = true; 118ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner } 119ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner return RetVal; 1207f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattner} 1217f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattner 1222240d2b3f7b9f5835868c83ce78d125d1b65212bChris Lattnerbool TailCallElim::runOnFunction(Function &F) { 1232240d2b3f7b9f5835868c83ce78d125d1b65212bChris Lattner // If this function is a varargs function, we won't be able to PHI the args 1242240d2b3f7b9f5835868c83ce78d125d1b65212bChris Lattner // right, so don't even try to convert it... 1252240d2b3f7b9f5835868c83ce78d125d1b65212bChris Lattner if (F.getFunctionType()->isVarArg()) return false; 1262240d2b3f7b9f5835868c83ce78d125d1b65212bChris Lattner 1272240d2b3f7b9f5835868c83ce78d125d1b65212bChris Lattner BasicBlock *OldEntry = 0; 128ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner bool TailCallsAreMarkedTail = false; 1292240d2b3f7b9f5835868c83ce78d125d1b65212bChris Lattner std::vector<PHINode*> ArgumentPHIs; 1302240d2b3f7b9f5835868c83ce78d125d1b65212bChris Lattner bool MadeChange = false; 1312240d2b3f7b9f5835868c83ce78d125d1b65212bChris Lattner 1327f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattner bool FunctionContainsEscapingAllocas = false; 1337f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattner 134ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner // CannotTCETailMarkedCall - If true, we cannot perform TCE on tail calls 135ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner // marked with the 'tail' attribute, because doing so would cause the stack 136ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner // size to increase (real TCE would deallocate variable sized allocas, TCE 137ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner // doesn't). 138ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner bool CannotTCETailMarkedCall = false; 139ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner 1407f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattner // Loop over the function, looking for any returning blocks, and keeping track 1417f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattner // of whether this function has any non-trivially used allocas. 1427f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattner for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) { 143ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner if (FunctionContainsEscapingAllocas && CannotTCETailMarkedCall) 144ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner break; 14500b16889ab461b7ecef1c91ade101186b7f1fce2Jeff Cohen 1464c0e4cdc40bbf94766242294fe386f4eb2d32d2eChris Lattner FunctionContainsEscapingAllocas |= 147ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner CheckForEscapingAllocas(BB, CannotTCETailMarkedCall); 1487f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattner } 14932b1e87f111d79f3f5b0e86c8f138c02bef8aa18Chris Lattner 15032b1e87f111d79f3f5b0e86c8f138c02bef8aa18Chris Lattner /// FIXME: The code generator produces really bad code when an 'escaping 15132b1e87f111d79f3f5b0e86c8f138c02bef8aa18Chris Lattner /// alloca' is changed from being a static alloca to being a dynamic alloca. 15232b1e87f111d79f3f5b0e86c8f138c02bef8aa18Chris Lattner /// Until this is resolved, disable this transformation if that would ever 15332b1e87f111d79f3f5b0e86c8f138c02bef8aa18Chris Lattner /// happen. This bug is PR962. 15432b1e87f111d79f3f5b0e86c8f138c02bef8aa18Chris Lattner if (FunctionContainsEscapingAllocas) 15532b1e87f111d79f3f5b0e86c8f138c02bef8aa18Chris Lattner return false; 15632b1e87f111d79f3f5b0e86c8f138c02bef8aa18Chris Lattner 157fd93908ae8b9684fe71c239e3c6cfe13ff6a2663Misha Brukman 158ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner // Second pass, change any tail calls to loops. 159ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) 160ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner if (ReturnInst *Ret = dyn_cast<ReturnInst>(BB->getTerminator())) 161ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner MadeChange |= ProcessReturningBlock(Ret, OldEntry, TailCallsAreMarkedTail, 162ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner ArgumentPHIs,CannotTCETailMarkedCall); 163ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner 164cf2f89251d45bc9783917874adb9029f71d50068Chris Lattner // If we eliminated any tail recursions, it's possible that we inserted some 165cf2f89251d45bc9783917874adb9029f71d50068Chris Lattner // silly PHI nodes which just merge an initial value (the incoming operand) 166cf2f89251d45bc9783917874adb9029f71d50068Chris Lattner // with themselves. Check to see if we did and clean up our mess if so. This 167cf2f89251d45bc9783917874adb9029f71d50068Chris Lattner // occurs when a function passes an argument straight through to its tail 168cf2f89251d45bc9783917874adb9029f71d50068Chris Lattner // call. 169cf2f89251d45bc9783917874adb9029f71d50068Chris Lattner if (!ArgumentPHIs.empty()) { 170cf2f89251d45bc9783917874adb9029f71d50068Chris Lattner for (unsigned i = 0, e = ArgumentPHIs.size(); i != e; ++i) { 171cf2f89251d45bc9783917874adb9029f71d50068Chris Lattner PHINode *PN = ArgumentPHIs[i]; 172cf2f89251d45bc9783917874adb9029f71d50068Chris Lattner 173cf2f89251d45bc9783917874adb9029f71d50068Chris Lattner // If the PHI Node is a dynamic constant, replace it with the value it is. 174ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner if (Value *PNV = PN->hasConstantValue()) { 175ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner PN->replaceAllUsesWith(PNV); 176ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner PN->eraseFromParent(); 177cf2f89251d45bc9783917874adb9029f71d50068Chris Lattner } 178cf2f89251d45bc9783917874adb9029f71d50068Chris Lattner } 179cf2f89251d45bc9783917874adb9029f71d50068Chris Lattner } 180cf2f89251d45bc9783917874adb9029f71d50068Chris Lattner 1817f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattner // Finally, if this function contains no non-escaping allocas, mark all calls 1827f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattner // in the function as eligible for tail calls (there is no stack memory for 1837f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattner // them to access). 1847f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattner if (!FunctionContainsEscapingAllocas) 1857f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattner for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) 1867f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattner for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) 1877f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattner if (CallInst *CI = dyn_cast<CallInst>(I)) 1887f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattner CI->setTailCall(); 1897f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattner 1902240d2b3f7b9f5835868c83ce78d125d1b65212bChris Lattner return MadeChange; 1912240d2b3f7b9f5835868c83ce78d125d1b65212bChris Lattner} 1927152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner 1937152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner 194543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner/// CanMoveAboveCall - Return true if it is safe to move the specified 195543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner/// instruction from after the call to before the call, assuming that all 196543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner/// instructions between the call and this instruction are movable. 197543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner/// 1987152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattnerbool TailCallElim::CanMoveAboveCall(Instruction *I, CallInst *CI) { 1997152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner // FIXME: We can move load/store/call/free instructions above the call if the 2007152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner // call does not mod/ref the memory location being processed. 2017152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner if (I->mayWriteToMemory() || isa<LoadInst>(I)) 2027152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner return false; 2037152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner 2047152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner // Otherwise, if this is a side-effect free instruction, check to make sure 2057152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner // that it does not use the return value of the call. If it doesn't use the 2067152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner // return value of the call, it must only use things that are defined before 2077152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner // the call, or movable instructions between the call and the instruction 2087152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner // itself. 2097152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) 2107152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner if (I->getOperand(i) == CI) 2117152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner return false; 2127152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner return true; 2137152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner} 2147152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner 215d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner// isDynamicConstant - Return true if the specified value is the same when the 216d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner// return would exit as it was when the initial iteration of the recursive 217d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner// function was executed. 218d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner// 219d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner// We currently handle static constants and arguments that are not modified as 220d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner// part of the recursion. 221d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner// 222d64152a70842b2f4186aa912938e69ca09c1434cChris Lattnerstatic bool isDynamicConstant(Value *V, CallInst *CI) { 223d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner if (isa<Constant>(V)) return true; // Static constants are always dyn consts 224d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner 225d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner // Check to see if this is an immutable argument, if so, the value 226d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner // will be available to initialize the accumulator. 227d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner if (Argument *Arg = dyn_cast<Argument>(V)) { 228d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner // Figure out which argument number this is... 229d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner unsigned ArgNo = 0; 230d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner Function *F = CI->getParent()->getParent(); 231e4d5c441e04bdc00ccf1804744af670655123b07Chris Lattner for (Function::arg_iterator AI = F->arg_begin(); &*AI != Arg; ++AI) 232d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner ++ArgNo; 233fd93908ae8b9684fe71c239e3c6cfe13ff6a2663Misha Brukman 234d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner // If we are passing this argument into call as the corresponding 235d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner // argument operand, then the argument is dynamically constant. 236d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner // Otherwise, we cannot transform this function safely. 237d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner if (CI->getOperand(ArgNo+1) == Arg) 238d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner return true; 239d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner } 240d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner // Not a constant or immutable argument, we can't safely transform. 241d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner return false; 242d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner} 243d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner 244d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner// getCommonReturnValue - Check to see if the function containing the specified 245d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner// return instruction and tail call consistently returns the same 246d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner// runtime-constant value at all exit points. If so, return the returned value. 247d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner// 248d64152a70842b2f4186aa912938e69ca09c1434cChris Lattnerstatic Value *getCommonReturnValue(ReturnInst *TheRI, CallInst *CI) { 249d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner Function *F = TheRI->getParent()->getParent(); 250d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner Value *ReturnedValue = 0; 251d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner 252d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner for (Function::iterator BBI = F->begin(), E = F->end(); BBI != E; ++BBI) 253d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner if (ReturnInst *RI = dyn_cast<ReturnInst>(BBI->getTerminator())) 254d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner if (RI != TheRI) { 255d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner Value *RetOp = RI->getOperand(0); 256d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner 257d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner // We can only perform this transformation if the value returned is 258d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner // evaluatable at the start of the initial invocation of the function, 259d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner // instead of at the end of the evaluation. 260d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner // 261d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner if (!isDynamicConstant(RetOp, CI)) 262d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner return 0; 263d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner 264d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner if (ReturnedValue && RetOp != ReturnedValue) 265d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner return 0; // Cannot transform if differing values are returned. 266d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner ReturnedValue = RetOp; 267d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner } 268d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner return ReturnedValue; 269d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner} 2707152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner 271543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner/// CanTransformAccumulatorRecursion - If the specified instruction can be 272543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner/// transformed using accumulator recursion elimination, return the constant 273543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner/// which is the start of the accumulator value. Otherwise return null. 274543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner/// 275543d622ef7505910c1cdc09ada0ab797c3437590Chris LattnerValue *TailCallElim::CanTransformAccumulatorRecursion(Instruction *I, 276543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner CallInst *CI) { 277543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner if (!I->isAssociative()) return 0; 278543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner assert(I->getNumOperands() == 2 && 279543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner "Associative operations should have 2 args!"); 280543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner 281543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // Exactly one operand should be the result of the call instruction... 282543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner if (I->getOperand(0) == CI && I->getOperand(1) == CI || 283543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner I->getOperand(0) != CI && I->getOperand(1) != CI) 284543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner return 0; 285543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner 286543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // The only user of this instruction we allow is a single return instruction. 287543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner if (!I->hasOneUse() || !isa<ReturnInst>(I->use_back())) 288543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner return 0; 289543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner 290543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // Ok, now we have to check all of the other return instructions in this 291543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // function. If they return non-constants or differing values, then we cannot 292543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // transform the function safely. 293d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner return getCommonReturnValue(cast<ReturnInst>(I->use_back()), CI); 294543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner} 295543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner 2967152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattnerbool TailCallElim::ProcessReturningBlock(ReturnInst *Ret, BasicBlock *&OldEntry, 297ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner bool &TailCallsAreMarkedTail, 298ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner std::vector<PHINode*> &ArgumentPHIs, 299ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner bool CannotTailCallElimCallsMarkedTail) { 3007152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner BasicBlock *BB = Ret->getParent(); 3017152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner Function *F = BB->getParent(); 3027152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner 3037152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner if (&BB->front() == Ret) // Make sure there is something before the ret... 3047152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner return false; 3058d9455d4e4f63c368f17b74a36b472fc61685310Chris Lattner 3068d9455d4e4f63c368f17b74a36b472fc61685310Chris Lattner // If the return is in the entry block, then making this transformation would 3078d9455d4e4f63c368f17b74a36b472fc61685310Chris Lattner // turn infinite recursion into an infinite loop. This transformation is ok 3088d9455d4e4f63c368f17b74a36b472fc61685310Chris Lattner // in theory, but breaks some code like: 3098d9455d4e4f63c368f17b74a36b472fc61685310Chris Lattner // double fabs(double f) { return __builtin_fabs(f); } // a 'fabs' call 3108d9455d4e4f63c368f17b74a36b472fc61685310Chris Lattner // disable this xform in this case, because the code generator will lower the 3118d9455d4e4f63c368f17b74a36b472fc61685310Chris Lattner // call to fabs into inline code. 3128d9455d4e4f63c368f17b74a36b472fc61685310Chris Lattner if (BB == &F->getEntryBlock()) 3138d9455d4e4f63c368f17b74a36b472fc61685310Chris Lattner return false; 3147152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner 3157152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner // Scan backwards from the return, checking to see if there is a tail call in 3167152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner // this block. If so, set CI to it. 3177152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner CallInst *CI; 3187152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner BasicBlock::iterator BBI = Ret; 3197152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner while (1) { 3207152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner CI = dyn_cast<CallInst>(BBI); 3217152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner if (CI && CI->getCalledFunction() == F) 3227152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner break; 3237152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner 3247152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner if (BBI == BB->begin()) 3257152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner return false; // Didn't find a potential tail call. 3267152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner --BBI; 3277152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner } 3287152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner 329ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner // If this call is marked as a tail call, and if there are dynamic allocas in 330ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner // the function, we cannot perform this optimization. 331ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner if (CI->isTailCall() && CannotTailCallElimCallsMarkedTail) 332ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner return false; 333ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner 334543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // If we are introducing accumulator recursion to eliminate associative 335543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // operations after the call instruction, this variable contains the initial 336543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // value for the accumulator. If this value is set, we actually perform 337543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // accumulator recursion elimination instead of simple tail recursion 338543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // elimination. 339543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner Value *AccumulatorRecursionEliminationInitVal = 0; 340543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner Instruction *AccumulatorRecursionInstr = 0; 341543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner 3427152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner // Ok, we found a potential tail call. We can currently only transform the 3437152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner // tail call if all of the instructions between the call and the return are 3447152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner // movable to above the call itself, leaving the call next to the return. 3457152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner // Check that this is the case now. 3467152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner for (BBI = CI, ++BBI; &*BBI != Ret; ++BBI) 347543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner if (!CanMoveAboveCall(BBI, CI)) { 348543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // If we can't move the instruction above the call, it might be because it 349543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // is an associative operation that could be tranformed using accumulator 350543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // recursion elimination. Check to see if this is the case, and if so, 351543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // remember the initial accumulator value for later. 352543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner if ((AccumulatorRecursionEliminationInitVal = 353543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner CanTransformAccumulatorRecursion(BBI, CI))) { 354543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // Yes, this is accumulator recursion. Remember which instruction 355543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // accumulates. 356543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner AccumulatorRecursionInstr = BBI; 357543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner } else { 358543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner return false; // Otherwise, we cannot eliminate the tail recursion! 359543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner } 360543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner } 3617152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner 3627152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner // We can only transform call/return pairs that either ignore the return value 363d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner // of the call and return void, ignore the value of the call and return a 364d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner // constant, return the value returned by the tail call, or that are being 365d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner // accumulator recursion variable eliminated. 366543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner if (Ret->getNumOperands() != 0 && Ret->getReturnValue() != CI && 3673b5f45042b17ad52815e3dd6c0c1df99f196dd04Chris Lattner !isa<UndefValue>(Ret->getReturnValue()) && 368d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner AccumulatorRecursionEliminationInitVal == 0 && 369d64152a70842b2f4186aa912938e69ca09c1434cChris Lattner !getCommonReturnValue(Ret, CI)) 3707152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner return false; 3717152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner 3727152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner // OK! We can transform this tail call. If this is the first one found, 3737152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner // create the new entry block, allowing us to branch back to the old entry. 3747152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner if (OldEntry == 0) { 3757152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner OldEntry = &F->getEntryBlock(); 3766934a04a8c15e9971cd1ea4d5c8df2d7afdd5be5Chris Lattner BasicBlock *NewEntry = new BasicBlock("", F, OldEntry); 3776934a04a8c15e9971cd1ea4d5c8df2d7afdd5be5Chris Lattner NewEntry->takeName(OldEntry); 3786934a04a8c15e9971cd1ea4d5c8df2d7afdd5be5Chris Lattner OldEntry->setName("tailrecurse"); 3797152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner new BranchInst(OldEntry, NewEntry); 380fd93908ae8b9684fe71c239e3c6cfe13ff6a2663Misha Brukman 381ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner // If this tail call is marked 'tail' and if there are any allocas in the 382ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner // entry block, move them up to the new entry block. 383ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner TailCallsAreMarkedTail = CI->isTailCall(); 384ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner if (TailCallsAreMarkedTail) 385ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner // Move all fixed sized allocas from OldEntry to NewEntry. 386ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner for (BasicBlock::iterator OEBI = OldEntry->begin(), E = OldEntry->end(), 387ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner NEBI = NewEntry->begin(); OEBI != E; ) 388ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner if (AllocaInst *AI = dyn_cast<AllocaInst>(OEBI++)) 389ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner if (isa<ConstantInt>(AI->getArraySize())) 3904bc5f8071a28b6fc4f4c2207dd03a5f747d0d84bChris Lattner AI->moveBefore(NEBI); 391ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner 3927152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner // Now that we have created a new block, which jumps to the entry 3937152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner // block, insert a PHI node for each argument of the function. 3947152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner // For now, we initialize each PHI to only have the real arguments 3957152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner // which are passed in. 3967152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner Instruction *InsertPos = OldEntry->begin(); 3977f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattner for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(); 3987f78f218fdb3515a61b995ac64f909bfd8ee84a7Chris Lattner I != E; ++I) { 3997152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner PHINode *PN = new PHINode(I->getType(), I->getName()+".tr", InsertPos); 4007152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner I->replaceAllUsesWith(PN); // Everyone use the PHI node now! 4017152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner PN->addIncoming(I, NewEntry); 4027152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner ArgumentPHIs.push_back(PN); 4037152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner } 4047152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner } 405fd93908ae8b9684fe71c239e3c6cfe13ff6a2663Misha Brukman 406ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner // If this function has self recursive calls in the tail position where some 407ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner // are marked tail and some are not, only transform one flavor or another. We 408ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner // have to choose whether we move allocas in the entry block to the new entry 409ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner // block or not, so we can't make a good choice for both. NOTE: We could do 410ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner // slightly better here in the case that the function has no entry block 411ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner // allocas. 412ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner if (TailCallsAreMarkedTail && !CI->isTailCall()) 413ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner return false; 414ce869ee05bfcb9d4750a3d0919a8260a727841c3Chris Lattner 4157152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner // Ok, now that we know we have a pseudo-entry block WITH all of the 4167152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner // required PHI nodes, add entries into the PHI node for the actual 4177152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner // parameters passed into the tail-recursive call. 4187152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner for (unsigned i = 0, e = CI->getNumOperands()-1; i != e; ++i) 4197152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner ArgumentPHIs[i]->addIncoming(CI->getOperand(i+1), BB); 420fd93908ae8b9684fe71c239e3c6cfe13ff6a2663Misha Brukman 421543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // If we are introducing an accumulator variable to eliminate the recursion, 422543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // do so now. Note that we _know_ that no subsequent tail recursion 423543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // eliminations will happen on this function because of the way the 424543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // accumulator recursion predicate is set up. 425543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // 426543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner if (AccumulatorRecursionEliminationInitVal) { 427543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner Instruction *AccRecInstr = AccumulatorRecursionInstr; 428543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // Start by inserting a new PHI node for the accumulator. 429543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner PHINode *AccPN = new PHINode(AccRecInstr->getType(), "accumulator.tr", 430543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner OldEntry->begin()); 431543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner 432543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // Loop over all of the predecessors of the tail recursion block. For the 433543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // real entry into the function we seed the PHI with the initial value, 434543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // computed earlier. For any other existing branches to this block (due to 435543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // other tail recursions eliminated) the accumulator is not modified. 436543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // Because we haven't added the branch in the current block to OldEntry yet, 437543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // it will not show up as a predecessor. 438543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner for (pred_iterator PI = pred_begin(OldEntry), PE = pred_end(OldEntry); 439543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner PI != PE; ++PI) { 440543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner if (*PI == &F->getEntryBlock()) 441543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner AccPN->addIncoming(AccumulatorRecursionEliminationInitVal, *PI); 442543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner else 443543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner AccPN->addIncoming(AccPN, *PI); 444543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner } 445543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner 446543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // Add an incoming argument for the current block, which is computed by our 447543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // associative accumulator instruction. 448543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner AccPN->addIncoming(AccRecInstr, BB); 449543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner 450543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // Next, rewrite the accumulator recursion instruction so that it does not 451543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // use the result of the call anymore, instead, use the PHI node we just 452543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // inserted. 453543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner AccRecInstr->setOperand(AccRecInstr->getOperand(0) != CI, AccPN); 454543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner 455543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // Finally, rewrite any return instructions in the program to return the PHI 456543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // node instead of the "initval" that they do currently. This loop will 457543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner // actually rewrite the return value we are destroying, but that's ok. 458543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner for (Function::iterator BBI = F->begin(), E = F->end(); BBI != E; ++BBI) 459543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner if (ReturnInst *RI = dyn_cast<ReturnInst>(BBI->getTerminator())) 460543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner RI->setOperand(0, AccPN); 461543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner ++NumAccumAdded; 462543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner } 463543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner 4647152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner // Now that all of the PHI nodes are in place, remove the call and 4657152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner // ret instructions, replacing them with an unconditional branch. 4667152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner new BranchInst(OldEntry, Ret); 4677152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner BB->getInstList().erase(Ret); // Remove return. 4687152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner BB->getInstList().erase(CI); // Remove call. 469543d622ef7505910c1cdc09ada0ab797c3437590Chris Lattner ++NumEliminated; 4707152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner return true; 4717152da38ef2c1f9f8ee407dc7740dfd43cbc41a6Chris Lattner} 472