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eliminate additions of 0.0 when they are obviously dead. This has to be careful to

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avoid turning -0.0 + 0.0 -> -0.0 which is incorrect.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@46499 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2008-01-29 06:52:45 +00:00
parent cca1867ab7
commit 2454a2e0c3
2 changed files with 62 additions and 0 deletions
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47
lib/Transforms/Scalar/InstructionCombining.cpp
View File

@ -1943,6 +1943,48 @@ Instruction *InstCombiner::FoldOpIntoPhi(Instruction &I) {
return ReplaceInstUsesWith(I, NewPN);
}
/// CannotBeNegativeZero - Return true if we can prove that the specified FP
/// value is never equal to -0.0.
///
/// Note that this function will need to be revisited when we support nondefault
/// rounding modes!
///
static bool CannotBeNegativeZero(const Value *V) {
if (const ConstantFP *CFP = dyn_cast<ConstantFP>(V))
return !CFP->getValueAPF().isNegZero();
// (add x, 0.0) is guaranteed to return +0.0, not -0.0.
if (const Instruction *I = dyn_cast<Instruction>(V)) {
if (I->getOpcode() == Instruction::Add &&
isa<ConstantFP>(I->getOperand(1)) &&
cast<ConstantFP>(I->getOperand(1))->isNullValue())
return true;
if (const IntrinsicInst *II = dyn_cast<IntrinsicInst>(I))
if (II->getIntrinsicID() == Intrinsic::sqrt)
return CannotBeNegativeZero(II->getOperand(1));
if (const CallInst *CI = dyn_cast<CallInst>(I))
if (const Function *F = CI->getCalledFunction()) {
if (F->isDeclaration()) {
switch (F->getNameLen()) {
case 3: // abs(x) != -0.0
if (!strcmp(F->getNameStart(), "abs")) return true;
break;
case 4: // abs[lf](x) != -0.0
if (!strcmp(F->getNameStart(), "absf")) return true;
if (!strcmp(F->getNameStart(), "absl")) return true;
break;
}
}
}
}
return false;
}
Instruction *InstCombiner::visitAdd(BinaryOperator &I) {
bool Changed = SimplifyCommutative(I);
Value *LHS = I.getOperand(0), *RHS = I.getOperand(1);
@ -2160,6 +2202,11 @@ Instruction *InstCombiner::visitAdd(BinaryOperator &I) {
return new SelectInst(SI->getCondition(), A, N);
}
}
// Check for X+0.0. Simplify it to X if we know X is not -0.0.
if (ConstantFP *CFP = dyn_cast<ConstantFP>(RHS))
if (CFP->getValueAPF().isPosZero() && CannotBeNegativeZero(LHS))
return ReplaceInstUsesWith(I, LHS);
return Changed ? &I : 0;
}

15
test/Transforms/InstCombine/zero-point-zero-add.ll Normal file
View File

@ -0,0 +1,15 @@
; RUN: llvm-as < %s | opt -instcombine | llvm-dis | grep 0.0 | count 1
declare double @abs(double)
define double @test(double %X) {
%Y = add double %X, 0.0 ;; Should be a single add x, 0.0
%Z = add double %Y, 0.0
ret double %Z
}
define double @test1(double %X) {
%Y = call double @abs(double %X)
%Z = add double %Y, 0.0
ret double %Z
}