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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
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30
lib/Transforms/InstCombine/InstCombineCasts.cpp
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@ -923,12 +923,6 @@ Instruction *InstCombiner::visitSExt(SExtInst &CI) {
Value *Src = CI.getOperand(0);
const Type *SrcTy = Src->getType(), *DestTy = CI.getType();
// Canonicalize sign-extend from i1 to a select.
if (Src->getType()->isInteger(1))
return SelectInst::Create(Src,
Constant::getAllOnesValue(CI.getType()),
Constant::getNullValue(CI.getType()));
// Attempt to extend the entire input expression tree to the destination
// type. Only do this if the dest type is a simple type, don't convert the
// expression tree to something weird like i93 unless the source is also
@ -968,6 +962,30 @@ Instruction *InstCombiner::visitSExt(SExtInst &CI) {
return BinaryOperator::CreateAShr(Res, ShAmt);
}
// (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
{
ICmpInst::Predicate Pred; Value *CmpLHS; ConstantInt *CmpRHS;
if (match(Src, m_ICmp(Pred, m_Value(CmpLHS), m_ConstantInt(CmpRHS)))) {
// 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 && CmpRHS->isZero()) ||
(Pred == ICmpInst::ICMP_SGT && CmpRHS->isAllOnesValue())) {
Value *Sh = ConstantInt::get(CmpLHS->getType(),
CmpLHS->getType()->getScalarSizeInBits()-1);
Value *In = Builder->CreateAShr(CmpLHS, Sh, CmpLHS->getName()+".lobit");
if (In->getType() != CI.getType())
In = Builder->CreateIntCast(In, CI.getType(), true/*SExt*/, "tmp");
if (Pred == ICmpInst::ICMP_SGT)
In = Builder->CreateNot(In, In->getName()+".not");
return ReplaceInstUsesWith(CI, In);
}
}
}
// If the input is a shl/ashr pair of a same constant, then this is a sign
// extension from a smaller value. If we could trust arbitrary bitwidth
// integers, we could turn this into a truncate to the smaller bit and then