[llvm] [InstCombine] Resolve TODO: nnan nsz X / -0.0 -> copysign(inf, X) (PR #79766)

[via llvm-commits]

https://github.com/AtariDreams updated https://github.com/llvm/llvm-project/pull/79766

>From 07de8a65273e75cb06abbecbea0dfe64d8bfea9d Mon Sep 17 00:00:00 2001
From: Rose <83477269+AtariDreams at users.noreply.github.com>
Date: Sun, 28 Jan 2024 15:04:34 -0500
Subject: [PATCH 1/2] [InstCombine] pre-commit tests (NFC)

---
 llvm/test/Transforms/InstCombine/fdiv.ll | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/llvm/test/Transforms/InstCombine/fdiv.ll b/llvm/test/Transforms/InstCombine/fdiv.ll
index c81a9ba6d4215..59984ce427f87 100644
--- a/llvm/test/Transforms/InstCombine/fdiv.ll
+++ b/llvm/test/Transforms/InstCombine/fdiv.ll
@@ -992,3 +992,22 @@ define float @fdiv_nnan_neg_zero_f32(float %x) {
   %fdiv = fdiv nnan float %x, -0.0
   ret float %fdiv
 }
+
+define double @test_positive_zero(double %X) {
+; CHECK-LABEL: @test_positive_zero(
+; CHECK-NEXT:    [[TMP1:%.*]] = call nnan nsz double @llvm.copysign.f64(double 0x7FF0000000000000, double [[X:%.*]])
+; CHECK-NEXT:    ret double [[TMP1]]
+;
+  %1 = fdiv nnan nsz double %X, 0.0
+  ret double %1
+}
+
+define double @test_negative_zero(double %X) {
+; CHECK-LABEL: @test_negative_zero(
+; CHECK-NEXT:    [[TMP1:%.*]] = fdiv nnan nsz double [[X:%.*]], -0.000000e+00
+; CHECK-NEXT:    ret double [[TMP1]]
+;
+  %1 = fdiv nnan nsz double %X, -0.0
+  ret double %1
+}
+

>From 8f81d98cd5f2102c6aab4db53d440be614270533 Mon Sep 17 00:00:00 2001
From: Rose <83477269+AtariDreams at users.noreply.github.com>
Date: Sun, 28 Jan 2024 13:30:29 -0500
Subject: [PATCH 2/2] [InstCombine] Resolve TODO: nnan nsz X / -0.0 ->
 copysign(inf, X)

---
 llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp | 6 ++++--
 llvm/test/Transforms/InstCombine/fdiv.ll                 | 2 +-
 2 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp b/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
index 6c3adf00c189a..f9cee9dfcfada 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
@@ -1598,9 +1598,11 @@ Instruction *InstCombinerImpl::foldFDivConstantDivisor(BinaryOperator &I) {
       return BinaryOperator::CreateFDivFMF(X, NegC, &I);
 
   // nnan X / +0.0 -> copysign(inf, X)
-  if (I.hasNoNaNs() && match(I.getOperand(1), m_Zero())) {
+  // nnan nsz X / -0.0 -> copysign(inf, X)
+  if (I.hasNoNaNs() &&
+      (match(I.getOperand(1), m_PosZeroFP()) ||
+       (I.hasNoSignedZeros() && match(I.getOperand(1), m_AnyZeroFP())))) {
     IRBuilder<> B(&I);
-    // TODO: nnan nsz X / -0.0 -> copysign(inf, X)
     CallInst *CopySign = B.CreateIntrinsic(
         Intrinsic::copysign, {C->getType()},
         {ConstantFP::getInfinity(I.getType()), I.getOperand(0)}, &I);
diff --git a/llvm/test/Transforms/InstCombine/fdiv.ll b/llvm/test/Transforms/InstCombine/fdiv.ll
index 59984ce427f87..e0aeb68402233 100644
--- a/llvm/test/Transforms/InstCombine/fdiv.ll
+++ b/llvm/test/Transforms/InstCombine/fdiv.ll
@@ -1004,7 +1004,7 @@ define double @test_positive_zero(double %X) {
 
 define double @test_negative_zero(double %X) {
 ; CHECK-LABEL: @test_negative_zero(
-; CHECK-NEXT:    [[TMP1:%.*]] = fdiv nnan nsz double [[X:%.*]], -0.000000e+00
+; CHECK-NEXT:    [[TMP1:%.*]] = call nnan nsz double @llvm.copysign.f64(double 0x7FF0000000000000, double [[X:%.*]])
 ; CHECK-NEXT:    ret double [[TMP1]]
 ;
   %1 = fdiv nnan nsz double %X, -0.0