From: Sanjay Patel <spatel@rotateright.com>
Date: Thu, 11 Jul 2019 13:44:29 +0000 (+0000)
Subject: [InstCombine] don't move FP negation out of a constant expression
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=f2f36cde314665b0b936c6682779203de1a7324f;p=llvm

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

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

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@365774 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp b/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
index a9e3e5f00f6..73172877d9e 100644
--- a/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
+++ b/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
@@ -374,11 +374,13 @@ Instruction *InstCombiner::visitFMul(BinaryOperator &I) {
     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
diff --git a/test/Transforms/InstCombine/fmul.ll b/test/Transforms/InstCombine/fmul.ll
index fcf0941c867..99b67dfa845 100644
--- a/test/Transforms/InstCombine/fmul.ll
+++ b/test/Transforms/InstCombine/fmul.ll
@@ -981,3 +981,16 @@ define float @fmul_fdiv_factor_extra_use(float %x, float %y) {
   %mul = fmul reassoc float %div, %y
   ret float %mul
 }
+
+; Avoid infinite looping by moving negation out of a constant expression.
+
+@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
+}