[llvm] llvm-reduce: Preserve original callsite calling conv when removing arguments (PR #133411)

[Matt Arsenault via llvm-commits]

https://github.com/arsenm updated https://github.com/llvm/llvm-project/pull/133411

>From c88f4efd0e169f74e350d687533dca9959accd04 Mon Sep 17 00:00:00 2001
From: Matt Arsenault <Matthew.Arsenault at amd.com>
Date: Fri, 28 Mar 2025 16:43:21 +0700
Subject: [PATCH] llvm-reduce: Preserve original callsite calling conv when
 removing arguments

In undefined mismatch cases, this was fixing the callsite to use the calling
convention of the new function. Preserve the original wrong callsite's calling
convention.
---
 .../remove-arguments-preserve-wrong-cc.ll     | 27 +++++++++++++++++++
 .../llvm-reduce/deltas/ReduceArguments.cpp    |  2 +-
 2 files changed, 28 insertions(+), 1 deletion(-)
 create mode 100644 llvm/test/tools/llvm-reduce/remove-arguments-preserve-wrong-cc.ll

diff --git a/llvm/test/tools/llvm-reduce/remove-arguments-preserve-wrong-cc.ll b/llvm/test/tools/llvm-reduce/remove-arguments-preserve-wrong-cc.ll
new file mode 100644
index 0000000000000..463b06c5d248a
--- /dev/null
+++ b/llvm/test/tools/llvm-reduce/remove-arguments-preserve-wrong-cc.ll
@@ -0,0 +1,27 @@
+; Check that when removing arguments, incorrect callsite calling conventions 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: @fastcc_callee(
+define fastcc i32 @fastcc_callee(i32 %a, i32 %b) {
+  ret i32 %a
+}
+
+; INTERESTING-LABEL: @fastcc_callee_decl(
+declare fastcc i32 @fastcc_callee_decl(i32 %a, i32 %b)
+
+; INTERESTING-LABEL: @caller_wrong_callsites(
+; INTERESTING: call
+; INTERESTING: call
+
+; RESULT-LABEL: define i32 @caller_wrong_callsites()
+; RESULT: %call0 = call coldcc i32 @fastcc_callee()
+; RESULT: %call1 = call i32 @fastcc_callee_decl()
+define i32 @caller_wrong_callsites(i32 %x) {
+  %call0 = call coldcc i32 @fastcc_callee(i32 %x, i32 2)
+  %call1 = call ccc i32 @fastcc_callee_decl(i32 %x, i32 2)
+  %result = add i32 %call0, %call1
+  ret i32 %result
+}
+
diff --git a/llvm/tools/llvm-reduce/deltas/ReduceArguments.cpp b/llvm/tools/llvm-reduce/deltas/ReduceArguments.cpp
index a7689688fdc2b..f1b72a75564de 100644
--- a/llvm/tools/llvm-reduce/deltas/ReduceArguments.cpp
+++ b/llvm/tools/llvm-reduce/deltas/ReduceArguments.cpp
@@ -65,7 +65,7 @@ static void replaceFunctionCalls(Function &OldF, Function &NewF,
       CI->getOperandBundlesAsDefs(OpBundles);
 
       CallInst *NewCI = CallInst::Create(&NewF, Args, OpBundles);
-      NewCI->setCallingConv(NewF.getCallingConv());
+      NewCI->setCallingConv(CI->getCallingConv());
 
       AttrBuilder CallSiteAttrs(Ctx, CI->getAttributes().getFnAttrs());
       NewCI->setAttributes(