Add redeclaration test

Author: mysterymath

clang/lib/Sema/SemaDeclAttr.cpp

@@ -6928,7 +6928,6 @@ static void handleModularFormat(Sema &S, Decl *D, const ParsedAttr &AL) {
   Aspects.erase(llvm::unique(Aspects), Aspects.end());
 
   // TODO: Type checking on identifier
-  // TODO: Merge attributes
   D->addAttr(::new (S.Context) ModularFormatAttr(
       S.Context, AL, AL.getArgAsIdent(0)->getIdentifierInfo(), ImplName,
       Aspects.data(), Aspects.size()));

clang/test/CodeGen/attr-modular-format.c

@@ -15,4 +15,14 @@ void test_explicit_format(void) {
   myprintf("hello");
 }
 
+int redecl(const char *fmt, ...) __attribute__((modular_format(__first_impl, "__first", "one"), format(printf, 1, 2)));
+int redecl(const char *fmt, ...) __attribute__((modular_format(__second_impl, "__second", "two", "three")));
+
+// CHECK-LABEL: define dso_local void @test_redecl(
+// CHECK:    {{.*}} = call i32 (ptr, ...) @redecl(ptr noundef @.str) #[[ATTR_REDECL:[0-9]+]]
+void test_redecl(void) {
+  redecl("hello");
+}
+
 // CHECK: attributes #[[ATTR]] = { "modular-format"="printf,1,2,__modular_printf,__printf,float" }
+// CHECK: attributes #[[ATTR_REDECL]] = { "modular-format"="printf,1,2,__second_impl,__second,three,two" }