Fix cpu-dispatch MV regression caused by r347812

r347812 permitted forward declarations for cpu-dispatch functions, which
are occassionally useful as exposition in  header files.  However, this inadvertently
permitted this function to become multiversioned after a usage.  This
patch ensures that the "CausesMV" checks are still run in the
forward-declaration case.

Change-Id: Icb6f975a2d068f088b89e3bbe26cf1d24f5a972c
llvm-svn: 351212

2 files changed, 10 insertions, 1 deletions

diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index e853180d76a..23c99d45a78 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -9816,7 +9816,8 @@ static bool CheckMultiVersionAdditionalDecl(
     return true;
   }
 
-  if (CheckMultiVersionAdditionalRules(S, OldFD, NewFD, false, NewMVType)) {
+  if (CheckMultiVersionAdditionalRules(S, OldFD, NewFD,
+                                       !OldFD->isMultiVersion(), NewMVType)) {
     NewFD->setInvalidDecl();
     return true;
   }
diff --git a/clang/test/Sema/attr-cpuspecific.c b/clang/test/Sema/attr-cpuspecific.c
index d15a65ea1fc..e87ad4de752 100644
--- a/clang/test/Sema/attr-cpuspecific.c
+++ b/clang/test/Sema/attr-cpuspecific.c
@@ -40,6 +40,14 @@ int __attribute__((cpu_dispatch(atom))) redecl2(void) { }
 int allow_fwd_decl(void);
 int __attribute__((cpu_dispatch(atom))) allow_fwd_decl(void) {}
 
+int allow_fwd_decl2(void);
+void use_fwd_decl(void) {
+  allow_fwd_decl2();
+}
+// expected-error@+1 {{function declaration cannot become a multiversioned function after first usage}}
+int __attribute__((cpu_dispatch(atom))) allow_fwd_decl2(void) {}
+
+
 int __attribute__((cpu_specific(atom))) redecl4(void);
 // expected-error@+1 {{function declaration is missing 'cpu_specific' or 'cpu_dispatch' attribute in a multiversioned function}}
 int redecl4(void);