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change the canonical form of "cond ? -1 : 0" to be

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"sext cond" instead of a select.  This simplifies some instcombine
code, matches the policy for zext (cond ? 1 : 0 -> zext), and allows
us to generate better code for a testcase on ppc.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@94339 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner
2010-01-24 00:09:49 +00:00
parent eb38ebf15c
commit abb992d6a3
6 changed files with 80 additions and 73 deletions
Download Patch File Download Diff File Expand all files Collapse all files
lib/Transforms/InstCombine/InstCombineSelect.cpp
+18 -48
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@@ -326,44 +326,6 @@ Instruction *InstCombiner::visitSelectInstWithICmp(SelectInst &SI,
break;
}
}
// (x <s 0) ? -1 : 0 -> ashr x, 31 -> all ones if signed
// (x >s -1) ? -1 : 0 -> ashr x, 31 -> all ones if not signed
CmpInst::Predicate Pred = CmpInst::BAD_ICMP_PREDICATE;
if (match(TrueVal, m_ConstantInt<-1>()) &&
match(FalseVal, m_ConstantInt<0>()))
Pred = ICI->getPredicate();
else if (match(TrueVal, m_ConstantInt<0>()) &&
match(FalseVal, m_ConstantInt<-1>()))
Pred = CmpInst::getInversePredicate(ICI->getPredicate());
if (Pred != CmpInst::BAD_ICMP_PREDICATE) {
// If we are just checking for a icmp eq of a single bit and zext'ing it
// to an integer, then shift the bit to the appropriate place and then
// cast to integer to avoid the comparison.
const APInt &Op1CV = CI->getValue();
// sext (x <s 0) to i32 --> x>>s31 true if signbit set.
// sext (x >s -1) to i32 --> (x>>s31)^-1 true if signbit clear.
if ((Pred == ICmpInst::ICMP_SLT && Op1CV == 0) ||
(Pred == ICmpInst::ICMP_SGT && Op1CV.isAllOnesValue())) {
Value *In = ICI->getOperand(0);
Value *Sh = ConstantInt::get(In->getType(),
In->getType()->getScalarSizeInBits()-1);
In = InsertNewInstBefore(BinaryOperator::CreateAShr(In, Sh,
In->getName()+".lobit"),
*ICI);
if (In->getType() != SI.getType())
In = CastInst::CreateIntegerCast(In, SI.getType(),
true/*SExt*/, "tmp", ICI);
if (Pred == ICmpInst::ICMP_SGT)
In = InsertNewInstBefore(BinaryOperator::CreateNot(In,
In->getName()+".not"), *ICI);
return ReplaceInstUsesWith(SI, In);
}
}
}
if (CmpLHS == TrueVal && CmpRHS == FalseVal) {
@@ -516,16 +478,25 @@ Instruction *InstCombiner::visitSelectInst(SelectInst &SI) {
if (ConstantInt *TrueValC = dyn_cast<ConstantInt>(TrueVal))
if (ConstantInt *FalseValC = dyn_cast<ConstantInt>(FalseVal)) {
// select C, 1, 0 -> zext C to int
if (FalseValC->isZero() && TrueValC->getValue() == 1) {
return CastInst::Create(Instruction::ZExt, CondVal, SI.getType());
} else if (TrueValC->isZero() && FalseValC->getValue() == 1) {
// select C, 0, 1 -> zext !C to int
Value *NotCond =
InsertNewInstBefore(BinaryOperator::CreateNot(CondVal,
"not."+CondVal->getName()), SI);
return CastInst::Create(Instruction::ZExt, NotCond, SI.getType());
if (FalseValC->isZero() && TrueValC->getValue() == 1)
return new ZExtInst(CondVal, SI.getType());
// select C, -1, 0 -> sext C to int
if (FalseValC->isZero() && TrueValC->isAllOnesValue())
return new SExtInst(CondVal, SI.getType());
// select C, 0, 1 -> zext !C to int
if (TrueValC->isZero() && FalseValC->getValue() == 1) {
Value *NotCond = Builder->CreateNot(CondVal, "not."+CondVal->getName());
return new ZExtInst(NotCond, SI.getType());
}
// select C, 0, -1 -> sext !C to int
if (TrueValC->isZero() && FalseValC->isAllOnesValue()) {
Value *NotCond = Builder->CreateNot(CondVal, "not."+CondVal->getName());
return new SExtInst(NotCond, SI.getType());
}
if (ICmpInst *IC = dyn_cast<ICmpInst>(SI.getCondition())) {
// If one of the constants is zero (we know they can't both be) and we
// have an icmp instruction with zero, and we have an 'and' with the
@@ -547,8 +518,7 @@ Instruction *InstCombiner::visitSelectInst(SelectInst &SI) {
ShouldNotVal ^= IC->getPredicate() == ICmpInst::ICMP_NE;
Value *V = ICA;
if (ShouldNotVal)
V = InsertNewInstBefore(BinaryOperator::Create(
Instruction::Xor, V, ICA->getOperand(1)), SI);
V = Builder->CreateXor(V, ICA->getOperand(1));
return ReplaceInstUsesWith(SI, V);
}
}