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Remove an InstCombine that transformed patterns like (x * uitofp i1 y) to (select y, x, 0.0) when the multiply has fast math flags set.

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While this might seem like an obvious canonicalization, there is one subtle problem with it.  The result of the original expression
is undef when x is NaN (remember, fast math flags), but the result of the select is always defined when x is NaN.  This means that the
new expression is strictly more defined than the original one.  One unfortunate consequence of this is that the transform is not reversible!
It's always legal to make increase the defined-ness of an expression, but it's not legal to reduce it.  Thus, targets that prefer the original
form of the expression cannot reverse the transform to recover it.  Another way to think of it is that the transform has lost source-level
information (the fast math flags), which is undesirable.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@215825 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Owen Anderson 2014-08-17 03:51:29 +00:00
parent 48c67ed949
commit 7a0201c6a6
2 changed files with 0 additions and 132 deletions
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30
lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
View File

@ -611,36 +611,6 @@ Instruction *InstCombiner::visitFMul(BinaryOperator &I) {
}
}
// B * (uitofp i1 C) -> select C, B, 0
if (I.hasNoNaNs() && I.hasNoInfs() && I.hasNoSignedZeros()) {
Value *LHS = Op0, *RHS = Op1;
Value *B, *C;
if (!match(RHS, m_UIToFP(m_Value(C))))
std::swap(LHS, RHS);
if (match(RHS, m_UIToFP(m_Value(C))) &&
C->getType()->getScalarType()->isIntegerTy(1)) {
B = LHS;
Value *Zero = ConstantFP::getNegativeZero(B->getType());
return SelectInst::Create(C, B, Zero);
}
}
// A * (1 - uitofp i1 C) -> select C, 0, A
if (I.hasNoNaNs() && I.hasNoInfs() && I.hasNoSignedZeros()) {
Value *LHS = Op0, *RHS = Op1;
Value *A, *C;
if (!match(RHS, m_FSub(m_FPOne(), m_UIToFP(m_Value(C)))))
std::swap(LHS, RHS);
if (match(RHS, m_FSub(m_FPOne(), m_UIToFP(m_Value(C)))) &&
C->getType()->getScalarType()->isIntegerTy(1)) {
A = LHS;
Value *Zero = ConstantFP::getNegativeZero(A->getType());
return SelectInst::Create(C, Zero, A);
}
}
if (!isa<Constant>(Op1))
std::swap(Opnd0, Opnd1);
else

102
test/Transforms/InstCombine/add4.ll
View File

@ -1,102 +0,0 @@
; RUN: opt < %s -instcombine -S | FileCheck %s
define float @test1(float %A, float %B, i1 %C) {
EntryBlock:
;; A*(1 - uitofp i1 C) -> select C, 0, A
%cf = uitofp i1 %C to float
%mc = fsub float 1.000000e+00, %cf
%p1 = fmul fast float %A, %mc
ret float %p1
; CHECK-LABEL: @test1(
; CHECK: select i1 %C, float -0.000000e+00, float %A
}
define float @test2(float %A, float %B, i1 %C) {
EntryBlock:
;; B*(uitofp i1 C) -> select C, B, 0
%cf = uitofp i1 %C to float
%p2 = fmul fast float %B, %cf
ret float %p2
; CHECK-LABEL: @test2(
; CHECK: select i1 %C, float %B, float -0.000000e+00
}
define float @test3(float %A, float %B, i1 %C) {
EntryBlock:
;; select C, 0, B + select C, A, 0 -> select C, A, B
%cf = uitofp i1 %C to float
%s1 = select i1 %C, float 0.000000e+00, float %B
%s2 = select i1 %C, float %A, float 0.000000e+00
%sum = fadd fast float %s1, %s2
ret float %sum
; CHECK-LABEL: @test3(
; CHECK: select i1 %C, float %A, float %B
}
define float @test4(float %A, float %B, i1 %C) {
EntryBlock:
;; B*(uitofp i1 C) + A*(1 - uitofp i1 C) -> select C, A, B
%cf = uitofp i1 %C to float
%mc = fsub fast float 1.000000e+00, %cf
%p1 = fmul fast float %A, %mc
%p2 = fmul fast float %B, %cf
%s1 = fadd fast float %p2, %p1
ret float %s1
; CHECK-LABEL: @test4(
; CHECK: select i1 %C, float %B, float %A
}
define float @test5(float %A, float %B, i1 %C) {
EntryBlock:
;; A*(1 - uitofp i1 C) + B*(uitofp i1 C) -> select C, A, B
%cf = uitofp i1 %C to float
%mc = fsub fast float 1.000000e+00, %cf
%p1 = fmul fast float %A, %mc
%p2 = fmul fast float %B, %cf
%s1 = fadd fast float %p1, %p2
ret float %s1
; CHECK-LABEL: @test5(
; CHECK: select i1 %C, float %B, float %A
}
; PR15952
define float @test6(float %A, float %B, i32 %C) {
%cf = uitofp i32 %C to float
%mc = fsub float 1.000000e+00, %cf
%p1 = fmul fast float %A, %mc
ret float %p1
; CHECK-LABEL: @test6(
; CHECK: uitofp
}
define float @test7(float %A, float %B, i32 %C) {
%cf = uitofp i32 %C to float
%p2 = fmul fast float %B, %cf
ret float %p2
; CHECK-LABEL: @test7(
; CHECK: uitofp
}
define <4 x float> @test8(<4 x float> %A, <4 x float> %B, <4 x i1> %C) {
;; B*(uitofp i1 C) + A*(1 - uitofp i1 C) -> select C, A, B
%cf = uitofp <4 x i1> %C to <4 x float>
%mc = fsub fast <4 x float> <float 1.0, float 1.0, float 1.0, float 1.0>, %cf
%p1 = fmul fast <4 x float> %A, %mc
%p2 = fmul fast <4 x float> %B, %cf
%s1 = fadd fast <4 x float> %p2, %p1
ret <4 x float> %s1
; CHECK-LABEL: @test8(
; CHECK: select <4 x i1> %C, <4 x float> %B, <4 x float> %A
}
define <4 x float> @test9(<4 x float> %A, <4 x float> %B, <4 x i1> %C) {
;; A*(1 - uitofp i1 C) + B*(uitofp i1 C) -> select C, A, B
%cf = uitofp <4 x i1> %C to <4 x float>
%mc = fsub fast <4 x float> <float 1.0, float 1.0, float 1.0, float 1.0>, %cf
%p1 = fmul fast <4 x float> %A, %mc
%p2 = fmul fast <4 x float> %B, %cf
%s1 = fadd fast <4 x float> %p1, %p2
ret <4 x float> %s1
; CHECK-LABEL: @test9
; CHECK: select <4 x i1> %C, <4 x float> %B, <4 x float> %A
}