[llvm] goldsteinn/simplify fmul (PR #85345)

[via llvm-commits]

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

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


>From b7244bccd0d03c3280b95d91a2f5bec55ad14612 Mon Sep 17 00:00:00 2001
From: Noah Goldstein <goldstein.w.n at gmail.com>
Date: Thu, 14 Mar 2024 20:03:01 -0500
Subject: [PATCH 1/2] [InstSimply] Add tests for simplify `(fmul -x, +/-0)`;
 NFC

---
 .../InstSimplify/floating-point-arithmetic.ll  | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/llvm/test/Transforms/InstSimplify/floating-point-arithmetic.ll b/llvm/test/Transforms/InstSimplify/floating-point-arithmetic.ll
index b8244b1d508c62..9db62d7e5efc0f 100644
--- a/llvm/test/Transforms/InstSimplify/floating-point-arithmetic.ll
+++ b/llvm/test/Transforms/InstSimplify/floating-point-arithmetic.ll
@@ -211,6 +211,24 @@ 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:    [[R:%.*]] = fmul float [[F:%.*]], -0.000000e+00
+; CHECK-NEXT:    ret float [[R]]
+;
+  %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:    [[R:%.*]] = fmul float [[F:%.*]], 0.000000e+00
+; CHECK-NEXT:    ret float [[R]]
+;
+  %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(

>From 305e930735a97bd2b560d3b1dde396017b1f2e0c Mon Sep 17 00:00:00 2001
From: Noah Goldstein <goldstein.w.n at gmail.com>
Date: Thu, 14 Mar 2024 20:03:05 -0500
Subject: [PATCH 2/2] [InstSimply] Add tests for simplify `(fmul -x, +/-0)` ->
 `-/+0`

We already handle the `+x` case, and noticed it was missing in the bug
affecting #82555
---
 llvm/lib/Analysis/InstructionSimplify.cpp           | 13 ++++++++++---
 .../InstSimplify/floating-point-arithmetic.ll       |  6 ++----
 2 files changed, 12 insertions(+), 7 deletions(-)

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 9db62d7e5efc0f..9b913d68f4004e 100644
--- a/llvm/test/Transforms/InstSimplify/floating-point-arithmetic.ll
+++ b/llvm/test/Transforms/InstSimplify/floating-point-arithmetic.ll
@@ -213,8 +213,7 @@ define double @fmul_nnan_ninf_nneg_n0.0_commute(i127 %x) {
 
 define float @src_mul_nzero_neg(float nofpclass(inf nan pzero psub pnorm) %f) {
 ; CHECK-LABEL: @src_mul_nzero_neg(
-; CHECK-NEXT:    [[R:%.*]] = fmul float [[F:%.*]], -0.000000e+00
-; CHECK-NEXT:    ret float [[R]]
+; CHECK-NEXT:    ret float 0.000000e+00
 ;
   %r = fmul float %f, -0.0
   ret float %r
@@ -222,8 +221,7 @@ define float @src_mul_nzero_neg(float nofpclass(inf nan pzero psub pnorm) %f) {
 
 define float @src_mul_zero_neg(float nofpclass(inf nan pzero psub pnorm) %f) {
 ; CHECK-LABEL: @src_mul_zero_neg(
-; CHECK-NEXT:    [[R:%.*]] = fmul float [[F:%.*]], 0.000000e+00
-; CHECK-NEXT:    ret float [[R]]
+; CHECK-NEXT:    ret float -0.000000e+00
 ;
   %r = fmul float %f, 0.0
   ret float %r