[llvm] r365774 - [InstCombine] don't move FP negation out of a constant expression

[Sanjay Patel via llvm-commits]

Author: spatel
Date: Thu Jul 11 06:44:29 2019
New Revision: 365774

URL: http://llvm.org/viewvc/llvm-project?rev=365774&view=rev
Log:
[InstCombine] don't move FP negation out of a constant expression

-(X * ConstExpr) becomes X * (-ConstExpr), so don't reverse that
and infinite loop.

Modified:
    llvm/trunk/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
    llvm/trunk/test/Transforms/InstCombine/fmul.ll

Modified: llvm/trunk/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp?rev=365774&r1=365773&r2=365774&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp (original)
+++ llvm/trunk/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp Thu Jul 11 06:44:29 2019
@@ -374,11 +374,13 @@ Instruction *InstCombiner::visitFMul(Bin
     return BinaryOperator::CreateFMulFMF(X, ConstantExpr::getFNeg(C), &I);
 
   // Sink negation: -X * Y --> -(X * Y)
-  if (match(Op0, m_OneUse(m_FNeg(m_Value(X)))))
+  // But don't transform constant expressions because there's an inverse fold.
+  if (match(Op0, m_OneUse(m_FNeg(m_Value(X)))) && !isa<ConstantExpr>(Op0))
     return BinaryOperator::CreateFNegFMF(Builder.CreateFMulFMF(X, Op1, &I), &I);
 
   // Sink negation: Y * -X --> -(X * Y)
-  if (match(Op1, m_OneUse(m_FNeg(m_Value(X)))))
+  // But don't transform constant expressions because there's an inverse fold.
+  if (match(Op1, m_OneUse(m_FNeg(m_Value(X)))) && !isa<ConstantExpr>(Op1))
     return BinaryOperator::CreateFNegFMF(Builder.CreateFMulFMF(X, Op0, &I), &I);
 
   // fabs(X) * fabs(X) -> X * X

Modified: llvm/trunk/test/Transforms/InstCombine/fmul.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/fmul.ll?rev=365774&r1=365773&r2=365774&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/InstCombine/fmul.ll (original)
+++ llvm/trunk/test/Transforms/InstCombine/fmul.ll Thu Jul 11 06:44:29 2019
@@ -981,3 +981,16 @@ define float @fmul_fdiv_factor_extra_use
   %mul = fmul reassoc float %div, %y
   ret float %mul
 }
+
+; Avoid infinite looping by moving negation out of a constant expression.
+
+ at g = external global {[2 x i8*]}, align 1
+
+define double @fmul_negated_constant_expression(double %x) {
+; CHECK-LABEL: @fmul_negated_constant_expression(
+; CHECK-NEXT:    [[R:%.*]] = fmul double [[X:%.*]], fsub (double -0.000000e+00, double bitcast (i64 ptrtoint (i8** getelementptr inbounds ({ [2 x i8*] }, { [2 x i8*] }* @g, i64 0, inrange i32 0, i64 2) to i64) to double))
+; CHECK-NEXT:    ret double [[R]]
+;
+  %r = fmul double %x, fsub (double -0.000000e+00, double bitcast (i64 ptrtoint (i8** getelementptr inbounds ({ [2 x i8*] }, { [2 x i8*] }* @g, i64 0, inrange i32 0, i64 2) to i64) to double))
+  ret double %r
+}