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Allow "exhaustive" trip count evaluation on phi nodes with all

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constant operands.

llvm-svn: 106537
This commit is contained in:
Dan Gohman 2010-06-22 13:15:46 +00:00
parent 981ff4464c
commit a3bc6b13f7
2 changed files with 26 additions and 9 deletions
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16
lib/Analysis/ScalarEvolution.cpp
View File

@ -4133,8 +4133,7 @@ static PHINode *getConstantEvolvingPHI(Value *V, const Loop *L) {
// constant or derived from a PHI node themselves.
PHINode *PHI = 0;
for (unsigned Op = 0, e = I->getNumOperands(); Op != e; ++Op)
if (!(isa<Constant>(I->getOperand(Op)) ||
isa<GlobalValue>(I->getOperand(Op)))) {
if (!isa<Constant>(I->getOperand(Op))) {
PHINode *P = getConstantEvolvingPHI(I->getOperand(Op), L);
if (P == 0) return 0; // Not evolving from PHI
if (PHI == 0)
@ -4155,11 +4154,9 @@ static Constant *EvaluateExpression(Value *V, Constant *PHIVal,
const TargetData *TD) {
if (isa<PHINode>(V)) return PHIVal;
if (Constant *C = dyn_cast<Constant>(V)) return C;
if (GlobalValue *GV = dyn_cast<GlobalValue>(V)) return GV;
Instruction *I = cast<Instruction>(V);
std::vector<Constant*> Operands;
Operands.resize(I->getNumOperands());
std::vector<Constant*> Operands(I->getNumOperands());
for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) {
Operands[i] = EvaluateExpression(I->getOperand(i), PHIVal, TD);
@ -4201,8 +4198,8 @@ ScalarEvolution::getConstantEvolutionLoopExitValue(PHINode *PN,
return RetVal = 0; // Must be a constant.
Value *BEValue = PN->getIncomingValue(SecondIsBackedge);
PHINode *PN2 = getConstantEvolvingPHI(BEValue, L);
if (PN2 != PN)
if (getConstantEvolvingPHI(BEValue, L) != PN &&
!isa<Constant>(BEValue))
return RetVal = 0; // Not derived from same PHI.
// Execute the loop symbolically to determine the exit value.
@ -4249,8 +4246,9 @@ ScalarEvolution::ComputeBackedgeTakenCountExhaustively(const Loop *L,
if (StartCST == 0) return getCouldNotCompute(); // Must be a constant.
Value *BEValue = PN->getIncomingValue(SecondIsBackedge);
PHINode *PN2 = getConstantEvolvingPHI(BEValue, L);
if (PN2 != PN) return getCouldNotCompute(); // Not derived from same PHI.
if (getConstantEvolvingPHI(BEValue, L) != PN &&
!isa<Constant>(BEValue))
return getCouldNotCompute(); // Not derived from same PHI.
// Okay, we find a PHI node that defines the trip count of this loop. Execute
// the loop symbolically to determine when the condition gets a value of

19
test/Analysis/ScalarEvolution/trip-count10.ll
View File

@ -105,3 +105,22 @@ bb2:
retbb:
ret void
}
; PHI nodes with all constant operands.
; CHECK: Determining loop execution counts for: @constant_phi_operands
; CHECK: Loop %loop: backedge-taken count is 1
; CHECK: Loop %loop: max backedge-taken count is 1
define void @constant_phi_operands() nounwind {
entry:
br label %loop
loop:
%i = phi i64 [ 1, %loop ], [ 0, %entry ]
%exitcond = icmp eq i64 %i, 1
br i1 %exitcond, label %return, label %loop
return:
ret void
}