From 7a0201c6a60d95a4afd6434a790526c6217b111f Mon Sep 17 00:00:00 2001 From: Owen Anderson Date: Sun, 17 Aug 2014 03:51:29 +0000 Subject: [PATCH] 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. 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 --- .../InstCombine/InstCombineMulDivRem.cpp | 30 ------ test/Transforms/InstCombine/add4.ll | 102 ------------------ 2 files changed, 132 deletions(-) delete mode 100644 test/Transforms/InstCombine/add4.ll diff --git a/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp b/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp index acfc96efa23..e7b8ed71486 100644 --- a/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp +++ b/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp @@ -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(Op1)) std::swap(Opnd0, Opnd1); else diff --git a/test/Transforms/InstCombine/add4.ll b/test/Transforms/InstCombine/add4.ll deleted file mode 100644 index f9b7e3b5a07..00000000000 --- a/test/Transforms/InstCombine/add4.ll +++ /dev/null @@ -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> , %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> , %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 -} -- 2.34.1