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[InstCombine] recode icmp fold in a vector-friendly way; NFC 

The transform in question:
icmp (and (trunc W), C2), C1 -> icmp (and W, C2'), C1'

...is still not enabled for vectors, thus no functional change intended.
It's not clear to me if this is a good transform for vectors or even
scalars in general. Changing that behavior may be a follow-on patch.

llvm-svn: 280627
This commit is contained in:
Sanjay Patel 2016-09-04 14:32:15 +00:00
parent f0bc9db96e
commit 6b4909749b
1 changed files with 30 additions and 22 deletions
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52
llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
View File

@ -1498,39 +1498,47 @@ Instruction *InstCombiner::foldICmpAndShift(ICmpInst &Cmp, BinaryOperator *And,
Instruction *InstCombiner::foldICmpAndConstConst(ICmpInst &Cmp,
BinaryOperator *And,
const APInt *C1) {
// FIXME: This check restricts all folds under here to scalar types.
ConstantInt *RHS = dyn_cast<ConstantInt>(Cmp.getOperand(1));
if (!RHS)
return nullptr;
// FIXME: Use m_APInt.
auto *C2 = dyn_cast<ConstantInt>(And->getOperand(1));
if (!C2)
const APInt *C2;
if (!match(And->getOperand(1), m_APInt(C2)))
return nullptr;
if (!And->hasOneUse() || !And->getOperand(0)->hasOneUse())
return nullptr;
// If the LHS is an AND of a truncating cast, we can widen the and/compare to
// be the input width without changing the value produced, eliminating a cast.
if (TruncInst *Cast = dyn_cast<TruncInst>(And->getOperand(0))) {
// We can do this transformation if either the AND constant does not have
// its sign bit set or if it is an equality comparison. Extending a
// relational comparison when we're checking the sign bit would not work.
if (Cmp.isEquality() || (!C2->isNegative() && C1->isNonNegative())) {
Value *NewAnd = Builder->CreateAnd(
Cast->getOperand(0), ConstantExpr::getZExt(C2, Cast->getSrcTy()));
NewAnd->takeName(And);
return new ICmpInst(Cmp.getPredicate(), NewAnd,
ConstantExpr::getZExt(RHS, Cast->getSrcTy()));
// If the LHS is an 'and' of a truncate and we can widen the and/compare to
// the input width without changing the value produced, eliminate the cast:
//
// icmp (and (trunc W), C2), C1 -> icmp (and W, C2'), C1'
//
// We can do this transformation if the constants do not have their sign bits
// set or if it is an equality comparison. Extending a relational comparison
// when we're checking the sign bit would not work.
Value *W;
if (match(And->getOperand(0), m_Trunc(m_Value(W))) &&
(Cmp.isEquality() || (!C1->isNegative() && !C2->isNegative()))) {
// TODO: Is this a good transform for vectors? Wider types may reduce
// throughput. Should this transform be limited (even for scalars) by using
// ShouldChangeType()?
if (!Cmp.getType()->isVectorTy()) {
Type *WideType = W->getType();
unsigned WideScalarBits = WideType->getScalarSizeInBits();
Constant *ZextC1 = ConstantInt::get(WideType, C1->zext(WideScalarBits));
Constant *ZextC2 = ConstantInt::get(WideType, C2->zext(WideScalarBits));
Value *NewAnd = Builder->CreateAnd(W, ZextC2, And->getName());
return new ICmpInst(Cmp.getPredicate(), NewAnd, ZextC1);
}
}
if (Instruction *I = foldICmpAndShift(Cmp, And, C1))
return I;
// FIXME: This check restricts all folds under here to scalar types.
ConstantInt *RHS = dyn_cast<ConstantInt>(Cmp.getOperand(1));
if (!RHS)
return nullptr;
// (icmp pred (and (or (lshr A, B), A), 1), 0) -->
// (icmp pred (and A, (or (shl 1, B), 1), 0))
// (icmp pred (and A, (or (shl 1, B), 1), 0))
//
// iff pred isn't signed
{
@ -1573,7 +1581,7 @@ Instruction *InstCombiner::foldICmpAndConstConst(ICmpInst &Cmp,
// Replace ((X & C2) > C1) with ((X & C2) != 0), if any bit set in (X & C2)
// will produce a result greater than C1.
if (Cmp.getPredicate() == ICmpInst::ICMP_UGT) {
unsigned NTZ = C2->getValue().countTrailingZeros();
unsigned NTZ = C2->countTrailingZeros();
if ((NTZ < C2->getBitWidth()) &&
APInt::getOneBitSet(C2->getBitWidth(), NTZ).ugt(*C1))
return new ICmpInst(ICmpInst::ICMP_NE, And,