Remove an InstCombine that transformed patterns like (x * uitofp i1 y) to (select...

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

diff --git a/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp b/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
index acfc96efa23a8bf9437bca48a39f3d6075c0c03a..e7b8ed71486d16b1fc64a2933a50c61f6267a168 100644 (file)
--- 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<Constant>(Op1))
       std::swap(Opnd0, Opnd1);
     else

diff --git a/test/Transforms/InstCombine/add4.ll b/test/Transforms/InstCombine/add4.ll
deleted file mode 100644 (file)
index f9b7e3b..0000000
--- 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> <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
-}