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[LoopFlatten][LoopInfo] Use Loop to identify latch compare instruction 

Make getLatchCmpInst non-static and use it in LoopFlatten as a more
robust way of identifying the compare.

Differential Revision: https://reviews.llvm.org/D106256
This commit is contained in:
Rosie Sumpter 2021-07-15 14:08:30 +01:00
parent 724f0e2abb
commit 44c9adb414
3 changed files with 14 additions and 15 deletions
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3
llvm/include/llvm/Analysis/LoopInfo.h
View File

@ -589,6 +589,9 @@ public:
/// ///
PHINode *getCanonicalInductionVariable() const; PHINode *getCanonicalInductionVariable() const;
/// Get the latch condition instruction.
ICmpInst *getLatchCmpInst() const;
/// Obtain the unique incoming and back edge. Return false if they are /// Obtain the unique incoming and back edge. Return false if they are
/// non-unique or the loop is dead; otherwise, return true. /// non-unique or the loop is dead; otherwise, return true.
bool getIncomingAndBackEdge(BasicBlock *&Incoming, bool getIncomingAndBackEdge(BasicBlock *&Incoming,

8
llvm/lib/Analysis/LoopInfo.cpp
View File

@ -171,8 +171,8 @@ PHINode *Loop::getCanonicalInductionVariable() const {
} }
/// Get the latch condition instruction. /// Get the latch condition instruction.
static ICmpInst *getLatchCmpInst(const Loop &L) { ICmpInst *Loop::getLatchCmpInst() const {
if (BasicBlock *Latch = L.getLoopLatch()) if (BasicBlock *Latch = getLoopLatch())
if (BranchInst *BI = dyn_cast_or_null<BranchInst>(Latch->getTerminator())) if (BranchInst *BI = dyn_cast_or_null<BranchInst>(Latch->getTerminator()))
if (BI->isConditional()) if (BI->isConditional())
return dyn_cast<ICmpInst>(BI->getCondition()); return dyn_cast<ICmpInst>(BI->getCondition());
@ -183,7 +183,7 @@ static ICmpInst *getLatchCmpInst(const Loop &L) {
/// Return the final value of the loop induction variable if found. /// Return the final value of the loop induction variable if found.
static Value *findFinalIVValue(const Loop &L, const PHINode &IndVar, static Value *findFinalIVValue(const Loop &L, const PHINode &IndVar,
const Instruction &StepInst) { const Instruction &StepInst) {
ICmpInst *LatchCmpInst = getLatchCmpInst(L); ICmpInst *LatchCmpInst = L.getLatchCmpInst();
if (!LatchCmpInst) if (!LatchCmpInst)
return nullptr; return nullptr;
@ -297,7 +297,7 @@ PHINode *Loop::getInductionVariable(ScalarEvolution &SE) const {
BasicBlock *Header = getHeader(); BasicBlock *Header = getHeader();
assert(Header && "Expected a valid loop header"); assert(Header && "Expected a valid loop header");
ICmpInst *CmpInst = getLatchCmpInst(*this); ICmpInst *CmpInst = getLatchCmpInst();
if (!CmpInst) if (!CmpInst)
return nullptr; return nullptr;

18
llvm/lib/Transforms/Scalar/LoopFlatten.cpp
View File

@ -111,15 +111,6 @@ static bool findLoopComponents(
LLVM_DEBUG(dbgs() << "Exiting and latch block are different\n"); LLVM_DEBUG(dbgs() << "Exiting and latch block are different\n");
return false; return false;
} }
// Latch block must end in a conditional branch.
BackBranch = dyn_cast<BranchInst>(Latch->getTerminator());
if (!BackBranch || !BackBranch->isConditional()) {
LLVM_DEBUG(dbgs() << "Could not find back-branch\n");
return false;
}
IterationInstructions.insert(BackBranch);
LLVM_DEBUG(dbgs() << "Found back branch: "; BackBranch->dump());
bool ContinueOnTrue = L->contains(BackBranch->getSuccessor(0));
// Find the induction PHI. If there is no induction PHI, we can't do the // Find the induction PHI. If there is no induction PHI, we can't do the
// transformation. TODO: could other variables trigger this? Do we have to // transformation. TODO: could other variables trigger this? Do we have to
@ -131,6 +122,7 @@ static bool findLoopComponents(
} }
LLVM_DEBUG(dbgs() << "Found induction PHI: "; InductionPHI->dump()); LLVM_DEBUG(dbgs() << "Found induction PHI: "; InductionPHI->dump());
bool ContinueOnTrue = L->contains(Latch->getTerminator()->getSuccessor(0));
auto IsValidPredicate = [&](ICmpInst::Predicate Pred) { auto IsValidPredicate = [&](ICmpInst::Predicate Pred) {
if (ContinueOnTrue) if (ContinueOnTrue)
return Pred == CmpInst::ICMP_NE || Pred == CmpInst::ICMP_ULT; return Pred == CmpInst::ICMP_NE || Pred == CmpInst::ICMP_ULT;
@ -138,13 +130,17 @@ static bool findLoopComponents(
return Pred == CmpInst::ICMP_EQ; return Pred == CmpInst::ICMP_EQ;
}; };
// Find Compare and make sure it is valid // Find Compare and make sure it is valid. getLatchCmpInst checks that the
ICmpInst *Compare = dyn_cast<ICmpInst>(BackBranch->getCondition()); // back branch of the latch is conditional.
ICmpInst *Compare = L->getLatchCmpInst();
if (!Compare || !IsValidPredicate(Compare->getUnsignedPredicate()) || if (!Compare || !IsValidPredicate(Compare->getUnsignedPredicate()) ||
Compare->hasNUsesOrMore(2)) { Compare->hasNUsesOrMore(2)) {
LLVM_DEBUG(dbgs() << "Could not find valid comparison\n"); LLVM_DEBUG(dbgs() << "Could not find valid comparison\n");
return false; return false;
} }
BackBranch = cast<BranchInst>(Latch->getTerminator());
IterationInstructions.insert(BackBranch);
LLVM_DEBUG(dbgs() << "Found back branch: "; BackBranch->dump());
IterationInstructions.insert(Compare); IterationInstructions.insert(Compare);
LLVM_DEBUG(dbgs() << "Found comparison: "; Compare->dump()); LLVM_DEBUG(dbgs() << "Found comparison: "; Compare->dump());