[clang] 4c02ab8 - Change prototype merging error into a warning for builtins

[Aaron Ballman via cfe-commits]

Author: Aaron Ballman
Date: 2022-08-09T11:36:48-04:00
New Revision: 4c02ab8c9742f6c32b17f49a306b3b072486f5c5

URL: https://github.com/llvm/llvm-project/commit/4c02ab8c9742f6c32b17f49a306b3b072486f5c5
DIFF: https://github.com/llvm/llvm-project/commit/4c02ab8c9742f6c32b17f49a306b3b072486f5c5.diff

LOG: Change prototype merging error into a warning for builtins

As was observed in https://reviews.llvm.org/D123627#3707635, it's
confusing that a user can write:
```
float rintf(void) {}
```
and get a warning, but writing:
```
float rintf() {}
```
gives an error. This patch changes the behavior so that both are
warnings, so that users who have functions which conflict with a
builtin identifier can still use that identifier as they wish.

Differential Revision: https://reviews.llvm.org/D131499

Added: 
    

Modified: 
    clang/lib/Sema/SemaDecl.cpp
    clang/test/Sema/prototype-redecls.c

Removed: 
    


################################################################################
diff  --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index 605e4bf0abae..c3011c09a6dc 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -4042,7 +4042,7 @@ bool Sema::MergeFunctionDecl(FunctionDecl *New, NamedDecl *&OldD, Scope *S,
     // default argument promotion rules were already checked by
     // ASTContext::typesAreCompatible().
     if (Old->hasPrototype() && !New->hasWrittenPrototype() && NewDeclIsDefn &&
-        Old->getNumParams() != New->getNumParams()) {
+        Old->getNumParams() != New->getNumParams() && !Old->isImplicit()) {
       if (Old->hasInheritedPrototype())
         Old = Old->getCanonicalDecl();
       Diag(New->getLocation(), diag::err_conflicting_types) << New;

diff  --git a/clang/test/Sema/prototype-redecls.c b/clang/test/Sema/prototype-redecls.c
index ed569b5223ce..49305db10d24 100644
--- a/clang/test/Sema/prototype-redecls.c
+++ b/clang/test/Sema/prototype-redecls.c
@@ -29,7 +29,7 @@ void garp(x) int x; {}
 
 // Ensure redeclarations that conflict with a builtin use a note which makes it
 // clear that the previous declaration was a builtin.
-float rintf() { // expected-error {{conflicting types for 'rintf'}} \
+float rintf() { // expected-warning {{incompatible redeclaration of library function 'rintf'}} \
                    expected-note {{'rintf' is a builtin with type 'float (float)'}}
   return 1.0f;
 }