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Enhance ScalarEvolution::isKnownPredicate with support for 

loop conditions which are invariants.

llvm-svn: 100995
This commit is contained in:
Dan Gohman 2010-04-11 22:16:48 +00:00
parent f7f28511a9
commit 07591698ce
2 changed files with 40 additions and 8 deletions
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7
llvm/include/llvm/Analysis/ScalarEvolution.h
View File

@ -380,6 +380,13 @@ namespace llvm {
Constant *getConstantEvolutionLoopExitValue(PHINode *PN, const APInt& BEs,
const Loop *L);
/// isKnownPredicateWithRanges - Test if the given expression is known to
/// satisfy the condition described by Pred and the known constant ranges
/// of LHS and RHS.
///
bool isKnownPredicateWithRanges(ICmpInst::Predicate Pred,
const SCEV *LHS, const SCEV *RHS);
public:
static char ID; // Pass identification, replacement for typeid
ScalarEvolution();

41
llvm/lib/Analysis/ScalarEvolution.cpp
View File

@ -4651,10 +4651,35 @@ bool ScalarEvolution::isKnownNonZero(const SCEV *S) {
bool ScalarEvolution::isKnownPredicate(ICmpInst::Predicate Pred,
const SCEV *LHS, const SCEV *RHS) {
// If LHS or RHS is an addrec, check to see if the condition is true in
// every iteration of the loop.
if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(LHS))
if (isLoopEntryGuardedByCond(
AR->getLoop(), Pred, AR->getStart(), RHS) &&
isLoopBackedgeGuardedByCond(
AR->getLoop(), Pred,
getAddExpr(AR, AR->getStepRecurrence(*this)), RHS))
return true;
if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(RHS))
if (isLoopEntryGuardedByCond(
AR->getLoop(), Pred, LHS, AR->getStart()) &&
isLoopBackedgeGuardedByCond(
AR->getLoop(), Pred,
LHS, getAddExpr(AR, AR->getStepRecurrence(*this))))
return true;
// Otherwise see what can be done with known constant ranges.
return isKnownPredicateWithRanges(Pred, LHS, RHS);
}
bool
ScalarEvolution::isKnownPredicateWithRanges(ICmpInst::Predicate Pred,
const SCEV *LHS, const SCEV *RHS) {
if (HasSameValue(LHS, RHS))
return ICmpInst::isTrueWhenEqual(Pred);
// This code is split out from isKnownPredicate because it is called from
// within isLoopEntryGuardedByCond.
switch (Pred) {
default:
llvm_unreachable("Unexpected ICmpInst::Predicate value!");
@ -5026,26 +5051,26 @@ ScalarEvolution::isImpliedCondOperandsHelper(ICmpInst::Predicate Pred,
break;
case ICmpInst::ICMP_SLT:
case ICmpInst::ICMP_SLE:
if (isKnownPredicate(ICmpInst::ICMP_SLE, LHS, FoundLHS) &&
isKnownPredicate(ICmpInst::ICMP_SGE, RHS, FoundRHS))
if (isKnownPredicateWithRanges(ICmpInst::ICMP_SLE, LHS, FoundLHS) &&
isKnownPredicateWithRanges(ICmpInst::ICMP_SGE, RHS, FoundRHS))
return true;
break;
case ICmpInst::ICMP_SGT:
case ICmpInst::ICMP_SGE:
if (isKnownPredicate(ICmpInst::ICMP_SGE, LHS, FoundLHS) &&
isKnownPredicate(ICmpInst::ICMP_SLE, RHS, FoundRHS))
if (isKnownPredicateWithRanges(ICmpInst::ICMP_SGE, LHS, FoundLHS) &&
isKnownPredicateWithRanges(ICmpInst::ICMP_SLE, RHS, FoundRHS))
return true;
break;
case ICmpInst::ICMP_ULT:
case ICmpInst::ICMP_ULE:
if (isKnownPredicate(ICmpInst::ICMP_ULE, LHS, FoundLHS) &&
isKnownPredicate(ICmpInst::ICMP_UGE, RHS, FoundRHS))
if (isKnownPredicateWithRanges(ICmpInst::ICMP_ULE, LHS, FoundLHS) &&
isKnownPredicateWithRanges(ICmpInst::ICMP_UGE, RHS, FoundRHS))
return true;
break;
case ICmpInst::ICMP_UGT:
case ICmpInst::ICMP_UGE:
if (isKnownPredicate(ICmpInst::ICMP_UGE, LHS, FoundLHS) &&
isKnownPredicate(ICmpInst::ICMP_ULE, RHS, FoundRHS))
if (isKnownPredicateWithRanges(ICmpInst::ICMP_UGE, LHS, FoundLHS) &&
isKnownPredicateWithRanges(ICmpInst::ICMP_ULE, RHS, FoundRHS))
return true;
break;
}