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(
26 SmallVector<RuntimePointerChecking::PointerCheck, 4> Checks,
27 const LoopAccessInfo &LAI, Loop *L, LoopInfo *LI, DominatorTree *DT)
28 : VersionedLoop(L), NonVersionedLoop(nullptr), Checks(std::move(Checks)),
29 LAI(LAI), LI(LI), DT(DT) {
30 assert(L->getExitBlock() && "No single exit block");
31 assert(L->getLoopPreheader() && "No preheader");
34 LoopVersioning::LoopVersioning(const LoopAccessInfo &LAInfo, Loop *L,
35 LoopInfo *LI, DominatorTree *DT)
36 : VersionedLoop(L), NonVersionedLoop(nullptr),
37 Checks(LAInfo.getRuntimePointerChecking()->getChecks()), LAI(LAInfo),
39 assert(L->getExitBlock() && "No single exit block");
40 assert(L->getLoopPreheader() && "No preheader");
43 void LoopVersioning::versionLoop(
44 const SmallVectorImpl<Instruction *> &DefsUsedOutside) {
45 Instruction *FirstCheckInst;
46 Instruction *MemRuntimeCheck;
47 // Add the memcheck in the original preheader (this is empty initially).
48 BasicBlock *MemCheckBB = VersionedLoop->getLoopPreheader();
49 std::tie(FirstCheckInst, MemRuntimeCheck) =
50 LAI.addRuntimeChecks(MemCheckBB->getTerminator(), Checks);
51 assert(MemRuntimeCheck && "called even though needsAnyChecking = false");
53 // Rename the block to make the IR more readable.
54 MemCheckBB->setName(VersionedLoop->getHeader()->getName() + ".lver.memcheck");
56 // Create empty preheader for the loop (and after cloning for the
57 // non-versioned loop).
58 BasicBlock *PH = SplitBlock(MemCheckBB, MemCheckBB->getTerminator(), DT, LI);
59 PH->setName(VersionedLoop->getHeader()->getName() + ".ph");
61 // Clone the loop including the preheader.
63 // FIXME: This does not currently preserve SimplifyLoop because the exit
64 // block is a join between the two loops.
65 SmallVector<BasicBlock *, 8> NonVersionedLoopBlocks;
67 cloneLoopWithPreheader(PH, MemCheckBB, VersionedLoop, VMap, ".lver.orig",
68 LI, DT, NonVersionedLoopBlocks);
69 remapInstructionsInBlocks(NonVersionedLoopBlocks, VMap);
71 // Insert the conditional branch based on the result of the memchecks.
72 Instruction *OrigTerm = MemCheckBB->getTerminator();
73 BranchInst::Create(NonVersionedLoop->getLoopPreheader(),
74 VersionedLoop->getLoopPreheader(), MemRuntimeCheck,
76 OrigTerm->eraseFromParent();
78 // The loops merge in the original exit block. This is now dominated by the
80 DT->changeImmediateDominator(VersionedLoop->getExitBlock(), MemCheckBB);
82 // Adds the necessary PHI nodes for the versioned loops based on the
83 // loop-defined values used outside of the loop.
84 addPHINodes(DefsUsedOutside);
87 void LoopVersioning::addPHINodes(
88 const SmallVectorImpl<Instruction *> &DefsUsedOutside) {
89 BasicBlock *PHIBlock = VersionedLoop->getExitBlock();
90 assert(PHIBlock && "No single successor to loop exit block");
92 for (auto *Inst : DefsUsedOutside) {
93 auto *NonVersionedLoopInst = cast<Instruction>(VMap[Inst]);
96 // First see if we have a single-operand PHI with the value defined by the
98 for (auto I = PHIBlock->begin(); (PN = dyn_cast<PHINode>(I)); ++I) {
99 assert(PN->getNumOperands() == 1 &&
100 "Exit block should only have on predecessor");
101 if (PN->getIncomingValue(0) == Inst)
106 PN = PHINode::Create(Inst->getType(), 2, Inst->getName() + ".lver",
108 for (auto *User : Inst->users())
109 if (!VersionedLoop->contains(cast<Instruction>(User)->getParent()))
110 User->replaceUsesOfWith(Inst, PN);
111 PN->addIncoming(Inst, VersionedLoop->getExitingBlock());
113 // Add the new incoming value from the non-versioned loop.
114 PN->addIncoming(NonVersionedLoopInst, NonVersionedLoop->getExitingBlock());