[InstCombine] Ensure Safe Handling of Flags in foldFNegIntoConstant

Author: SahilPatidar

llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp

@@ -2682,8 +2682,15 @@ static Instruction *foldFNegIntoConstant(Instruction &I, const DataLayout &DL) {
   // Fold negation into constant operand.
   // -(X * C) --> X * (-C)
   if (match(FNegOp, m_FMul(m_Value(X), m_Constant(C))))
-    if (Constant *NegC = ConstantFoldUnaryOpOperand(Instruction::FNeg, C, DL))
+    if (Constant *NegC = ConstantFoldUnaryOpOperand(Instruction::FNeg, C, DL)) {
+      if (match(C, m_AnyZeroFP()) && I.getFastMathFlags().noInfs()) {
+        return BinaryOperator::CreateFMulFMF(
+            X, NegC,
+            I.getFastMathFlags() &
+                cast<FPMathOperator>(I.getOperand(0))->getFastMathFlags());
+      }
       return BinaryOperator::CreateFMulFMF(X, NegC, &I);
+    }
   // -(X / C) --> X / (-C)
   if (match(FNegOp, m_FDiv(m_Value(X), m_Constant(C))))
     if (Constant *NegC = ConstantFoldUnaryOpOperand(Instruction::FNeg, C, DL))

llvm/test/Transforms/InstCombine/fneg.ll

@@ -1109,4 +1109,45 @@ define float @test_fneg_select_maxnum(float %x) {
   ret float %neg
 }
 
+define float @test_fneg_ninf_mul_with_anyzero(float %a) {
+; CHECK-LABEL: @test_fneg_ninf_mul_with_anyzero(
+; CHECK-NEXT:    [[F:%.*]] = fmul float [[A:%.*]], -0.000000e+00
+; CHECK-NEXT:    ret float [[F]]
+;
+  %mul = fmul float %a, 0.0
+  %f = fneg ninf float %mul
+  ret float %f
+}
+
+define float @test_fsub_ninf_mul_with_anyzero(float %a) {
+; CHECK-LABEL: @test_fsub_ninf_mul_with_anyzero(
+; CHECK-NEXT:    [[F2:%.*]] = fmul float [[A:%.*]], -0.000000e+00
+; CHECK-NEXT:    ret float [[F2]]
+;
+  %f1 = fmul float %a, 0.000000
+  %f2 = fsub ninf float -0.000000, %f1
+  ret float %f2
+}
+
+define float @test_fneg_nnan_mul_with_anyzero(float %a) {
+; CHECK-LABEL: @test_fneg_nnan_mul_with_anyzero(
+; CHECK-NEXT:    [[TMP1:%.*]] = fneg nnan float [[A:%.*]]
+; CHECK-NEXT:    [[F2:%.*]] = call nnan float @llvm.copysign.f32(float 0.000000e+00, float [[TMP1]])
+; CHECK-NEXT:    ret float [[F2]]
+;
+  %f1 = fmul float %a, 0.000000
+  %f2 = fneg nnan float %f1
+  ret float %f2
+}
+
+define float @test_fneg_nsz_mul_with_anyzero(float %a) {
+; CHECK-LABEL: @test_fneg_nsz_mul_with_anyzero(
+; CHECK-NEXT:    [[F2:%.*]] = fmul nsz float [[A:%.*]], -0.000000e+00
+; CHECK-NEXT:    ret float [[F2]]
+;
+  %f1 = fmul float %a, 0.000000
+  %f2 = fneg nsz float %f1
+  ret float %f2
+}
+
 !0 = !{}