[llvm] Resolving #171877 (PR #172139)

[Ron Xavier via llvm-commits]

https://github.com/Ronxvier updated https://github.com/llvm/llvm-project/pull/172139

>From ae2549c6b069e998021c1f42080640fa38658b46 Mon Sep 17 00:00:00 2001
From: Ron Xavier <Ronelxavi at gmail.com>
Date: Sat, 13 Dec 2025 03:45:49 -0500
Subject: [PATCH 1/3] Resolve #171877

Moved constant folding logic from SimplifyLibCalls.cpp to ConstantFoldLibCall2
---
 llvm/lib/Analysis/ConstantFolding.cpp          | 12 ++++++++++++
 llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp | 14 ++------------
 2 files changed, 14 insertions(+), 12 deletions(-)

diff --git a/llvm/lib/Analysis/ConstantFolding.cpp b/llvm/lib/Analysis/ConstantFolding.cpp
index a9b51065a1d99..8a73c02bc363e 100644
--- a/llvm/lib/Analysis/ConstantFolding.cpp
+++ b/llvm/lib/Analysis/ConstantFolding.cpp
@@ -3241,6 +3241,18 @@ static Constant *ConstantFoldLibCall2(StringRef Name, Type *Ty,
     if (TLI->has(Func))
       return ConstantFoldBinaryFP(atan2, Op1V, Op2V, Ty);
     break;
+  case LibFunc_fdim:
+  case LibFunc_fdimf:
+  case LibFunc_fdiml:
+      if (TLI->has(Func)){
+    APFloat Difference = Op1V;
+    Difference.subtract(Op2V, RoundingMode::NearestTiesToEven);
+
+    APFloat MaxVal =
+        maximum(Difference, APFloat::getZero(Ty->getFltSemantics()));
+    return ConstantFP::get(Ty->getContext(), MaxVal);
+  }
+  break;
   }
 
   return nullptr;
diff --git a/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp b/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
index c3537f544c432..55cd08b3de855 100644
--- a/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
@@ -3201,18 +3201,8 @@ Value *LibCallSimplifier::optimizeFdim(CallInst *CI, IRBuilderBase &B) {
   if (isa<PoisonValue>(CI->getArgOperand(1)))
     return CI->getArgOperand(1);
 
-  const APFloat *X, *Y;
-  // Check if both values are constants
-  if (!match(CI->getArgOperand(0), m_APFloat(X)) ||
-      !match(CI->getArgOperand(1), m_APFloat(Y)))
-    return nullptr;
-
-  APFloat Difference = *X;
-  Difference.subtract(*Y, RoundingMode::NearestTiesToEven);
-
-  APFloat MaxVal =
-      maximum(Difference, APFloat::getZero(CI->getType()->getFltSemantics()));
-  return ConstantFP::get(CI->getType(), MaxVal);
+  // Constant folding will be handled by ConstantFoldLibCall2
+  return nullptr;
 }
 
 //===----------------------------------------------------------------------===//

>From 9f6988ac52d3f3332f3582a0360a728b4373487c Mon Sep 17 00:00:00 2001
From: Ron Xavier <Ronelxavi at gmail.com>
Date: Sat, 13 Dec 2025 06:22:09 -0500
Subject: [PATCH 2/3] reformatted

---
 llvm/lib/Analysis/ConstantFolding.cpp | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/llvm/lib/Analysis/ConstantFolding.cpp b/llvm/lib/Analysis/ConstantFolding.cpp
index 8a73c02bc363e..901f0738cc6d4 100644
--- a/llvm/lib/Analysis/ConstantFolding.cpp
+++ b/llvm/lib/Analysis/ConstantFolding.cpp
@@ -3244,15 +3244,15 @@ static Constant *ConstantFoldLibCall2(StringRef Name, Type *Ty,
   case LibFunc_fdim:
   case LibFunc_fdimf:
   case LibFunc_fdiml:
-      if (TLI->has(Func)){
-    APFloat Difference = Op1V;
-    Difference.subtract(Op2V, RoundingMode::NearestTiesToEven);
+    if (TLI->has(Func)){
+      APFloat Difference = Op1V;
+      Difference.subtract(Op2V, RoundingMode::NearestTiesToEven);
 
-    APFloat MaxVal =
-        maximum(Difference, APFloat::getZero(Ty->getFltSemantics()));
-    return ConstantFP::get(Ty->getContext(), MaxVal);
-  }
-  break;
+      APFloat MaxVal =
+          maximum(Difference, APFloat::getZero(Ty->getFltSemantics()));
+      return ConstantFP::get(Ty->getContext(), MaxVal);
+    }
+    break;
   }
 
   return nullptr;

>From 5d9b081df2966fe8064355d03d8cf0f491a08ccd Mon Sep 17 00:00:00 2001
From: Ron Xavier <Ronelxavi at gmail.com>
Date: Sat, 13 Dec 2025 13:21:01 -0500
Subject: [PATCH 3/3] Update ConstantFolding.cpp

Might be an overguarding issue
---
 llvm/lib/Analysis/ConstantFolding.cpp | 12 +++++-------
 1 file changed, 5 insertions(+), 7 deletions(-)

diff --git a/llvm/lib/Analysis/ConstantFolding.cpp b/llvm/lib/Analysis/ConstantFolding.cpp
index 901f0738cc6d4..dd4a3abf8c89d 100644
--- a/llvm/lib/Analysis/ConstantFolding.cpp
+++ b/llvm/lib/Analysis/ConstantFolding.cpp
@@ -3244,14 +3244,12 @@ static Constant *ConstantFoldLibCall2(StringRef Name, Type *Ty,
   case LibFunc_fdim:
   case LibFunc_fdimf:
   case LibFunc_fdiml:
-    if (TLI->has(Func)){
-      APFloat Difference = Op1V;
-      Difference.subtract(Op2V, RoundingMode::NearestTiesToEven);
+    APFloat Difference = Op1V;
+    Difference.subtract(Op2V, RoundingMode::NearestTiesToEven);
 
-      APFloat MaxVal =
-          maximum(Difference, APFloat::getZero(Ty->getFltSemantics()));
-      return ConstantFP::get(Ty->getContext(), MaxVal);
-    }
+    APFloat MaxVal =
+      maximum(Difference, APFloat::getZero(Ty->getFltSemantics()));
+    return ConstantFP::get(Ty->getContext(), MaxVal);
     break;
   }