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SimplifyIndVar: make foldIVUser iterative to fold a chain of operands.

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@137199 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Andrew Trick 2011-08-10 04:01:31 +00:00
parent 4a1a5eb95b
commit ea23daa446
1 changed files with 26 additions and 12 deletions
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38
lib/Transforms/Utils/SimplifyIndVar.cpp
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@ -73,7 +73,7 @@ namespace {
/// all simplicitions to users of an IV.
void simplifyUsers(PHINode *CurrIV, IVVisitor *V = NULL);
bool foldIVUser(Instruction *UseInst, Instruction *IVOperand);
Value *foldIVUser(Instruction *UseInst, Instruction *IVOperand);
bool eliminateIVUser(Instruction *UseInst, Instruction *IVOperand);
void eliminateIVComparison(ICmpInst *ICmp, Value *IVOperand);
@ -84,26 +84,30 @@ namespace {
/// foldIVUser - Fold an IV operand into its use. This removes increments of an
/// aligned IV when used by a instruction that ignores the low bits.
bool SimplifyIndvar::foldIVUser(Instruction *UseInst, Instruction *IVOperand) {
///
/// Return the operand of IVOperand for this induction variable if IVOperand can
/// be folded (in case more folding opportunity has been exposed).
/// Otherwise return null.
Value *SimplifyIndvar::foldIVUser(Instruction *UseInst, Instruction *IVOperand) {
Value *IVSrc = 0;
unsigned OperIdx = 0;
const SCEV *FoldedExpr = 0;
switch (UseInst->getOpcode()) {
default:
return false;
return 0;
case Instruction::UDiv:
case Instruction::LShr:
// We're only interested in the case where we know something about
// the numerator and have a constant denominator.
if (IVOperand != UseInst->getOperand(OperIdx) ||
!isa<ConstantInt>(UseInst->getOperand(1)))
return false;
return 0;
// Attempt to fold a binary operator with constant operand.
// e.g. ((I + 1) >> 2) => I >> 2
if (IVOperand->getNumOperands() != 2 ||
!isa<ConstantInt>(IVOperand->getOperand(1)))
return false;
return 0;
IVSrc = IVOperand->getOperand(0);
// IVSrc must be the (SCEVable) IV, since the other operand is const.
@ -114,7 +118,7 @@ bool SimplifyIndvar::foldIVUser(Instruction *UseInst, Instruction *IVOperand) {
// Get a constant for the divisor. See createSCEV.
uint32_t BitWidth = cast<IntegerType>(UseInst->getType())->getBitWidth();
if (D->getValue().uge(BitWidth))
return false;
return 0;
D = ConstantInt::get(UseInst->getContext(),
APInt(BitWidth, 1).shl(D->getZExtValue()));
@ -123,11 +127,11 @@ bool SimplifyIndvar::foldIVUser(Instruction *UseInst, Instruction *IVOperand) {
}
// We have something that might fold it's operand. Compare SCEVs.
if (!SE->isSCEVable(UseInst->getType()))
return false;
return 0;
// Bypass the operand if SCEV can prove it has no effect.
if (SE->getSCEV(UseInst) != FoldedExpr)
return false;
return 0;
DEBUG(dbgs() << "INDVARS: Eliminated IV operand: " << *IVOperand
<< " -> " << *UseInst << '\n');
@ -139,7 +143,7 @@ bool SimplifyIndvar::foldIVUser(Instruction *UseInst, Instruction *IVOperand) {
Changed = true;
if (IVOperand->use_empty())
DeadInsts.push_back(IVOperand);
return true;
return IVSrc;
}
/// eliminateIVComparison - SimplifyIVUsers helper for eliminating useless
@ -337,10 +341,20 @@ void SimplifyIndvar::simplifyUsers(PHINode *CurrIV, IVVisitor *V) {
// Bypass back edges to avoid extra work.
if (UseOper.first == CurrIV) continue;
foldIVUser(UseOper.first, UseOper.second);
Instruction *IVOperand = UseOper.second;
for (unsigned N = 0; IVOperand; ++N) {
assert(N <= Simplified.size() && "runaway iteration");
if (eliminateIVUser(UseOper.first, UseOper.second)) {
pushIVUsers(UseOper.second, Simplified, SimpleIVUsers);
Value *NewOper = foldIVUser(UseOper.first, IVOperand);
if (!NewOper)
break; // done folding
IVOperand = dyn_cast<Instruction>(NewOper);
}
if (!IVOperand)
continue;
if (eliminateIVUser(UseOper.first, IVOperand)) {
pushIVUsers(IVOperand, Simplified, SimpleIVUsers);
continue;
}
CastInst *Cast = dyn_cast<CastInst>(UseOper.first);