1 //===- LoopVersioning.cpp - Utility to version a loop ---------------------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file defines a utility class to perform loop versioning. The versioned
11 // loop speculates that otherwise may-aliasing memory accesses don't overlap and
12 // emits checks to prove this.
14 //===----------------------------------------------------------------------===//
16 #include "llvm/Analysis/LoopAccessAnalysis.h"
17 #include "llvm/Analysis/LoopInfo.h"
18 #include "llvm/IR/Dominators.h"
19 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
20 #include "llvm/Transforms/Utils/Cloning.h"
21 #include "llvm/Transforms/Utils/LoopVersioning.h"
25 LoopVersioning::LoopVersioning(const LoopAccessInfo &LAI, Loop *L, LoopInfo *LI,
27 const SmallVector<int, 8> *PtrToPartition)
28 : VersionedLoop(L), NonVersionedLoop(nullptr),
29 PtrToPartition(PtrToPartition), LAI(LAI), LI(LI), DT(DT) {
30 assert(L->getExitBlock() && "No single exit block");
31 assert(L->getLoopPreheader() && "No preheader");
34 bool LoopVersioning::needsRuntimeChecks() const {
35 return LAI.getRuntimePointerCheck()->needsAnyChecking(PtrToPartition);
38 void LoopVersioning::versionLoop(Pass *P) {
39 Instruction *FirstCheckInst;
40 Instruction *MemRuntimeCheck;
41 // Add the memcheck in the original preheader (this is empty initially).
42 BasicBlock *MemCheckBB = VersionedLoop->getLoopPreheader();
43 std::tie(FirstCheckInst, MemRuntimeCheck) =
44 LAI.addRuntimeCheck(MemCheckBB->getTerminator(), PtrToPartition);
45 assert(MemRuntimeCheck && "called even though needsAnyChecking = false");
47 // Rename the block to make the IR more readable.
48 MemCheckBB->setName(VersionedLoop->getHeader()->getName() + ".lver.memcheck");
50 // Create empty preheader for the loop (and after cloning for the
51 // non-versioned loop).
52 BasicBlock *PH = SplitBlock(MemCheckBB, MemCheckBB->getTerminator(), DT, LI);
53 PH->setName(VersionedLoop->getHeader()->getName() + ".ph");
55 // Clone the loop including the preheader.
57 // FIXME: This does not currently preserve SimplifyLoop because the exit
58 // block is a join between the two loops.
59 SmallVector<BasicBlock *, 8> NonVersionedLoopBlocks;
61 cloneLoopWithPreheader(PH, MemCheckBB, VersionedLoop, VMap, ".lver.orig",
62 LI, DT, NonVersionedLoopBlocks);
63 remapInstructionsInBlocks(NonVersionedLoopBlocks, VMap);
65 // Insert the conditional branch based on the result of the memchecks.
66 Instruction *OrigTerm = MemCheckBB->getTerminator();
67 BranchInst::Create(NonVersionedLoop->getLoopPreheader(),
68 VersionedLoop->getLoopPreheader(), MemRuntimeCheck,
70 OrigTerm->eraseFromParent();
72 // The loops merge in the original exit block. This is now dominated by the
74 DT->changeImmediateDominator(VersionedLoop->getExitBlock(), MemCheckBB);
77 void LoopVersioning::addPHINodes(
78 const SmallVectorImpl<Instruction *> &DefsUsedOutside) {
79 BasicBlock *PHIBlock = VersionedLoop->getExitBlock();
80 assert(PHIBlock && "No single successor to loop exit block");
82 for (auto *Inst : DefsUsedOutside) {
83 auto *NonVersionedLoopInst = cast<Instruction>(VMap[Inst]);
86 // First see if we have a single-operand PHI with the value defined by the
88 for (auto I = PHIBlock->begin(); (PN = dyn_cast<PHINode>(I)); ++I) {
89 assert(PN->getNumOperands() == 1 &&
90 "Exit block should only have on predecessor");
91 if (PN->getIncomingValue(0) == Inst)
96 PN = PHINode::Create(Inst->getType(), 2, Inst->getName() + ".lver",
98 for (auto *User : Inst->users())
99 if (!VersionedLoop->contains(cast<Instruction>(User)->getParent()))
100 User->replaceUsesOfWith(Inst, PN);
101 PN->addIncoming(Inst, VersionedLoop->getExitingBlock());
103 // Add the new incoming value from the non-versioned loop.
104 PN->addIncoming(NonVersionedLoopInst, NonVersionedLoop->getExitingBlock());