[llvm] [InstSimply] Add tests for simplify `(fmul -x, +/-0)` -> `-/+0` (PR #85345)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-transforms

Author: None (goldsteinn)

<details>
<summary>Changes</summary>

- **[InstSimply] Add tests for simplify `(fmul -x, +/-0)`; NFC**
- **[InstSimply] Add tests for simplify `(fmul -x, +/-0)` -> `-/+0`**


---
Full diff: https://github.com/llvm/llvm-project/pull/85345.diff


2 Files Affected:

- (modified) llvm/lib/Analysis/InstructionSimplify.cpp (+10-3) 
- (modified) llvm/test/Transforms/InstSimplify/floating-point-arithmetic.ll (+16) 


``````````diff
diff --git a/llvm/lib/Analysis/InstructionSimplify.cpp b/llvm/lib/Analysis/InstructionSimplify.cpp
index ce651783caf16b..434ee26ef01aa5 100644
--- a/llvm/lib/Analysis/InstructionSimplify.cpp
+++ b/llvm/lib/Analysis/InstructionSimplify.cpp
@@ -5767,11 +5767,18 @@ static Value *simplifyFMAFMul(Value *Op0, Value *Op1, FastMathFlags FMF,
     if (FMF.noNaNs() && FMF.noSignedZeros())
       return ConstantFP::getZero(Op0->getType());
 
-    // +normal number * (-)0.0 --> (-)0.0
     KnownFPClass Known =
         computeKnownFPClass(Op0, FMF, fcInf | fcNan, /*Depth=*/0, Q);
-    if (Known.SignBit == false && Known.isKnownNever(fcInf | fcNan))
-      return Op1;
+    if (Known.isKnownNever(fcInf | fcNan)) {
+      // +normal number * (-)0.0 --> (-)0.0
+      if (Known.SignBit == false)
+        return Op1;
+      // -normal number * (-)0.0 --> -(-)0.0
+      if (Known.SignBit == true)
+        return match(Op1, m_PosZeroFP())
+                   ? ConstantFP::getNegativeZero(Op0->getType())
+                   : ConstantFP::getZero(Op0->getType());
+    }
   }
 
   // sqrt(X) * sqrt(X) --> X, if we can:
diff --git a/llvm/test/Transforms/InstSimplify/floating-point-arithmetic.ll b/llvm/test/Transforms/InstSimplify/floating-point-arithmetic.ll
index b8244b1d508c62..9b913d68f4004e 100644
--- a/llvm/test/Transforms/InstSimplify/floating-point-arithmetic.ll
+++ b/llvm/test/Transforms/InstSimplify/floating-point-arithmetic.ll
@@ -211,6 +211,22 @@ define double @fmul_nnan_ninf_nneg_n0.0_commute(i127 %x) {
   ret double %r
 }
 
+define float @src_mul_nzero_neg(float nofpclass(inf nan pzero psub pnorm) %f) {
+; CHECK-LABEL: @src_mul_nzero_neg(
+; CHECK-NEXT:    ret float 0.000000e+00
+;
+  %r = fmul float %f, -0.0
+  ret float %r
+}
+
+define float @src_mul_zero_neg(float nofpclass(inf nan pzero psub pnorm) %f) {
+; CHECK-LABEL: @src_mul_zero_neg(
+; CHECK-NEXT:    ret float -0.000000e+00
+;
+  %r = fmul float %f, 0.0
+  ret float %r
+}
+
 ; Make sure we can infer %x can't be 0 based on assumes.
 define { float, float } @test_fmul_0_assumed_finite(float %x) {
 ; CHECK-LABEL: @test_fmul_0_assumed_finite(

``````````

</details>


https://github.com/llvm/llvm-project/pull/85345