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Don't do (x - (y - z)) --> (x + (z - y)) on floating-point types, because

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it may round differently. This fixes PR4374.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@73243 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Dan Gohman 2009-06-12 19:23:25 +00:00
parent 194ae785e1
commit e54aba5fa9
2 changed files with 8 additions and 15 deletions
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15
lib/Transforms/Scalar/InstructionCombining.cpp
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@ -2608,21 +2608,6 @@ Instruction *InstCombiner::visitFSub(BinaryOperator &I) {
else if (Op1I->getOperand(1) == Op0) // X-(Y+X) == -Y
return BinaryOperator::CreateFNeg(Op1I->getOperand(0), I.getName());
}
if (Op1I->hasOneUse()) {
// Replace (x - (y - z)) with (x + (z - y)) if the (y - z) subexpression
// is not used by anyone else...
//
if (Op1I->getOpcode() == Instruction::FSub) {
// Swap the two operands of the subexpr...
Value *IIOp0 = Op1I->getOperand(0), *IIOp1 = Op1I->getOperand(1);
Op1I->setOperand(0, IIOp1);
Op1I->setOperand(1, IIOp0);
// Create the new top level fadd instruction...
return BinaryOperator::CreateFAdd(Op0, Op1);
}
}
}
return 0;

8
test/Transforms/InstCombine/fsub-fsub.ll Normal file
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@ -0,0 +1,8 @@
; RUN: llvm-as < %s | opt -instcombine | llvm-dis | grep fsub | count 2
; PR4374
define float @func(float %a, float %b) nounwind {
%tmp3 = fsub float %a, %b
%tmp4 = fsub float -0.000000e+00, %tmp3
ret float %tmp4
}