[clang] [clang][Sema][FMV] Add a note to the 'cannot become multiversioned diagnostic (PR #124364)

[Jon Roelofs via cfe-commits]

https://github.com/jroelofs created https://github.com/llvm/llvm-project/pull/124364

... pointing out the previous declaration.

>From 3a2d96d127a3c233f7352acb17ef4a3a6b0a0a0b Mon Sep 17 00:00:00 2001
From: Jon Roelofs <jonathan_roelofs at apple.com>
Date: Fri, 24 Jan 2025 15:01:18 -0800
Subject: [PATCH] [clang][Sema][FMV] Add a note to the 'cannot become
 multiversioned' diagnostic

... pointing out the previous declaration.
---
 clang/lib/Sema/SemaDecl.cpp           | 7 +++++--
 clang/test/Sema/attr-cpuspecific.c    | 3 ++-
 clang/test/Sema/attr-target-mv.c      | 3 ++-
 clang/test/Sema/attr-target-version.c | 3 ++-
 4 files changed, 11 insertions(+), 5 deletions(-)

diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index ad49eac66e98e5..4151d9f83c8d8e 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -11380,8 +11380,11 @@ static bool CheckMultiVersionAdditionalRules(Sema &S, const FunctionDecl *OldFD,
     return true;
 
   // Only allow transition to MultiVersion if it hasn't been used.
-  if (OldFD && CausesMV && OldFD->isUsed(false))
-    return S.Diag(NewFD->getLocation(), diag::err_multiversion_after_used);
+  if (OldFD && CausesMV && OldFD->isUsed(false)) {
+    S.Diag(NewFD->getLocation(), diag::err_multiversion_after_used);
+    S.Diag(OldFD->getLocation(), diag::note_previous_declaration);
+    return true;
+  }
 
   return S.areMultiversionVariantFunctionsCompatible(
       OldFD, NewFD, S.PDiag(diag::err_multiversion_noproto),
diff --git a/clang/test/Sema/attr-cpuspecific.c b/clang/test/Sema/attr-cpuspecific.c
index 3cd58f49faa5e6..238db0ac0b85dc 100644
--- a/clang/test/Sema/attr-cpuspecific.c
+++ b/clang/test/Sema/attr-cpuspecific.c
@@ -44,7 +44,8 @@ int allow_fwd_decl2(void);
 void use_fwd_decl(void) {
   allow_fwd_decl2();
 }
-// expected-error at +1 {{function declaration cannot become a multiversioned function after first usage}}
+// expected-error at +2 {{function declaration cannot become a multiversioned function after first usage}}
+// expected-note at -5 {{previous declaration is here}}
 int __attribute__((cpu_dispatch(atom))) allow_fwd_decl2(void) {}
 
 
diff --git a/clang/test/Sema/attr-target-mv.c b/clang/test/Sema/attr-target-mv.c
index ddb1d82b02f098..dfc3d614dc1e00 100644
--- a/clang/test/Sema/attr-target-mv.c
+++ b/clang/test/Sema/attr-target-mv.c
@@ -66,7 +66,8 @@ int use3(void) {
   return mv_after_use();
 }
 
-// expected-error at +1 {{function declaration cannot become a multiversioned function after first usage}}
+// expected-error at +2 {{function declaration cannot become a multiversioned function after first usage}}
+// expected-note at -6 {{previous declaration is here}}
 int __attribute__((target("arch=sandybridge")))  mv_after_use(void) { return 2; }
 
 int __attribute__((target("sse4.2,arch=sandybridge"))) mangle(void) { return 1; }
diff --git a/clang/test/Sema/attr-target-version.c b/clang/test/Sema/attr-target-version.c
index cfcc1622abe5c0..d062212848daf1 100644
--- a/clang/test/Sema/attr-target-version.c
+++ b/clang/test/Sema/attr-target-version.c
@@ -88,7 +88,8 @@ int bar() {
   nodef();
   return def();
 }
-// expected-error at +1 {{function declaration cannot become a multiversioned function after first usage}}
+// expected-error at +2 {{function declaration cannot become a multiversioned function after first usage}}
+// expected-note at -13 {{previous declaration is here}}
 int __attribute__((target_version("sha2"))) def(void) { return 1; }
 
 int __attribute__((target_version("sve"))) prot();