[llvm] llvm-reduce: Fix losing fast math flags when removing arguments (PR #133408)

[Matt Arsenault via llvm-commits]

https://github.com/arsenm updated https://github.com/llvm/llvm-project/pull/133408

>From 8bfe027d3f930ac661019858baaa0366513f405f Mon Sep 17 00:00:00 2001
From: Matt Arsenault <Matthew.Arsenault at amd.com>
Date: Fri, 28 Mar 2025 16:26:47 +0700
Subject: [PATCH] llvm-reduce: Fix losing fast math flags when removing
 arguments

---
 .../remove-arguments-preserve-fmf.ll          | 26 +++++++++++++++++++
 .../llvm-reduce/deltas/ReduceArguments.cpp    |  7 ++++-
 2 files changed, 32 insertions(+), 1 deletion(-)
 create mode 100644 llvm/test/tools/llvm-reduce/remove-arguments-preserve-fmf.ll

diff --git a/llvm/test/tools/llvm-reduce/remove-arguments-preserve-fmf.ll b/llvm/test/tools/llvm-reduce/remove-arguments-preserve-fmf.ll
new file mode 100644
index 0000000000000..2ceb3e717200b
--- /dev/null
+++ b/llvm/test/tools/llvm-reduce/remove-arguments-preserve-fmf.ll
@@ -0,0 +1,26 @@
+; Check that when removing arguments, existing fast math flags are preserved
+
+; RUN: llvm-reduce --abort-on-invalid-reduction --delta-passes=arguments --test FileCheck --test-arg --check-prefixes=INTERESTING --test-arg %s --test-arg --input-file %s -o %t
+; RUN: FileCheck --check-prefixes=RESULT %s < %t
+
+; INTERESTING-LABEL: @math_callee(
+define float @math_callee(float %a, float %b) {
+  %add = fadd float %a, %b
+  ret float %add
+}
+
+; INTERESTING-LABEL: @math_callee_decl(
+declare float @math_callee_decl(float %a, float %b)
+
+; INTERESTING-LABEL: @math_caller(
+; INTERESTING: call
+; INTERESTING: call
+
+; RESULT: %call0 = call nnan nsz float @math_callee()
+; RESULT: %call1 = call ninf float @math_callee_decl()
+define float @math_caller(float %x) {
+  %call0 = call nnan nsz float @math_callee(float %x, float 2.0)
+  %call1 = call ninf float @math_callee_decl(float %x, float 2.0)
+  %result = fadd float %call0, %call1
+  ret float %result
+}
diff --git a/llvm/tools/llvm-reduce/deltas/ReduceArguments.cpp b/llvm/tools/llvm-reduce/deltas/ReduceArguments.cpp
index ec2699a990311..b1bbcf8917b3c 100644
--- a/llvm/tools/llvm-reduce/deltas/ReduceArguments.cpp
+++ b/llvm/tools/llvm-reduce/deltas/ReduceArguments.cpp
@@ -16,8 +16,10 @@
 #include "Utils.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/IR/Constants.h"
+#include "llvm/IR/FMF.h"
 #include "llvm/IR/Instructions.h"
 #include "llvm/IR/Intrinsics.h"
+#include "llvm/IR/Operator.h"
 #include <set>
 #include <vector>
 
@@ -59,7 +61,7 @@ static void replaceFunctionCalls(Function &OldF, Function &NewF,
         }
       }
 
-      // FIXME: Losing bundles, fast math flags and metadata
+      // FIXME: Losing bundles and metadata
       CallInst *NewCI = CallInst::Create(&NewF, Args);
       NewCI->setCallingConv(NewF.getCallingConv());
 
@@ -73,6 +75,9 @@ static void replaceFunctionCalls(Function &OldF, Function &NewF,
            ++ArgI, ++AttrIdx)
         NewCI->addParamAttrs(AttrIdx, ArgAttrs[AttrIdx]);
 
+      if (auto *FPOp = dyn_cast<FPMathOperator>(NewCI))
+        cast<Instruction>(FPOp)->setFastMathFlags(CI->getFastMathFlags());
+
       if (!CI->use_empty())
         CI->replaceAllUsesWith(NewCI);
       ReplaceInstWithInst(CI, NewCI);