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Thread comparisons over udiv/sdiv/ashr/lshr exact and lshr nuw/nsw whenever

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possible. This goes into instcombine and instsimplify because instsimplify
doesn't need to check hasOneUse since it returns (almost exclusively) constants.

This fixes PR9343 #4 #5 and #8!


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@127064 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Nick Lewycky
2011-03-05 05:19:11 +00:00
parent 9feda1730c
commit 58bfcdbcf6
4 changed files with 109 additions and 1 deletions
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34
lib/Analysis/InstructionSimplify.cpp
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@@ -1344,7 +1344,7 @@ static Value *SimplifyICmpInst(unsigned Predicate, Value *LHS, Value *RHS,
// the compare, and if only one of them is then we moved it to RHS already.
if (isa<AllocaInst>(LHS) && (isa<GlobalValue>(RHS) || isa<AllocaInst>(RHS) ||
isa<ConstantPointerNull>(RHS)))
// We already know that LHS != LHS.
// We already know that LHS != RHS.
return ConstantInt::get(ITy, CmpInst::isFalseWhenEqual(Pred));
// If we are comparing with zero then try hard since this is a common case.
@@ -1700,6 +1700,38 @@ static Value *SimplifyICmpInst(unsigned Predicate, Value *LHS, Value *RHS,
}
}
if (MaxRecurse && LBO && RBO && LBO->getOpcode() == RBO->getOpcode() &&
LBO->getOperand(1) == RBO->getOperand(1)) {
switch (LBO->getOpcode()) {
default: break;
case Instruction::UDiv:
case Instruction::LShr:
if (ICmpInst::isSigned(Pred))
break;
// fall-through
case Instruction::SDiv:
case Instruction::AShr:
if (!LBO->isExact() && !RBO->isExact())
break;
if (Value *V = SimplifyICmpInst(Pred, LBO->getOperand(0),
RBO->getOperand(0), TD, DT, MaxRecurse-1))
return V;
break;
case Instruction::Shl: {
bool NUW = LBO->hasNoUnsignedWrap() && LBO->hasNoUnsignedWrap();
bool NSW = LBO->hasNoSignedWrap() && RBO->hasNoSignedWrap();
if (!NUW && !NSW)
break;
if (!NSW && ICmpInst::isSigned(Pred))
break;
if (Value *V = SimplifyICmpInst(Pred, LBO->getOperand(0),
RBO->getOperand(0), TD, DT, MaxRecurse-1))
return V;
break;
}
}
}
// If the comparison is with the result of a select instruction, check whether
// comparing with either branch of the select always yields the same value.
if (isa<SelectInst>(LHS) || isa<SelectInst>(RHS))