Correct 'target' default behavior on redecl, allow forward declaration.

Declarations without the attribute were disallowed because it would be
ambiguous which 'target' it was supposed to be on.  For example:

void ___attribute__((target("v1"))) foo();
void foo(); // Redecl of above, or fwd decl of below?
void ___attribute__((target("v2"))) foo();

However, a first declaration doesn't have that problem, and erroring
prevents it from working in cases where the forward declaration is
useful.

Additionally, a forward declaration of target==default wouldn't properly
cause multiversioning, so this patch fixes that.

The patch was not split since the 'default' fix would require
implementing the same check for that case, followed by undoing the same
change for the fwd-decl implementation.

Change-Id: I66f2c5bc2477bcd3f7544b9c16c83ece257077b0
llvm-svn: 347805

2 files changed, 53 insertions, 3 deletions

diff --git a/clang/test/CodeGen/attr-target-mv.c b/clang/test/CodeGen/attr-target-mv.c
index f9fbbbd5f0b..e22499e2928 100644
--- a/clang/test/CodeGen/attr-target-mv.c
+++ b/clang/test/CodeGen/attr-target-mv.c
@@ -35,10 +35,24 @@ void bar4() {
   foo_multi(1, 5.0);
 }
 
+int fwd_decl_default(void);
+int __attribute__((target("default"))) fwd_decl_default(void) { return 2; }
+
+int fwd_decl_avx(void);
+int __attribute__((target("avx"))) fwd_decl_avx(void) { return 2; }
+int __attribute__((target("default"))) fwd_decl_avx(void) { return 2; }
+
+void bar5() {
+  fwd_decl_default();
+  fwd_decl_avx();
+}
+
 // LINUX: @foo.ifunc = ifunc i32 (), i32 ()* ()* @foo.resolver
 // LINUX: @foo_inline.ifunc = ifunc i32 (), i32 ()* ()* @foo_inline.resolver
 // LINUX: @foo_decls.ifunc = ifunc void (), void ()* ()* @foo_decls.resolver
 // LINUX: @foo_multi.ifunc = ifunc void (i32, double), void (i32, double)* ()* @foo_multi.resolver
+// LINUX: @fwd_decl_default.ifunc = ifunc i32 (), i32 ()* ()* @fwd_decl_default.resolver
+// LINUX: @fwd_decl_avx.ifunc = ifunc i32 (), i32 ()* ()* @fwd_decl_avx.resolver
 
 // LINUX: define i32 @foo.sse4.2()
 // LINUX: ret i32 0
@@ -168,8 +182,45 @@ void bar4() {
 // WINDOWS: call void @foo_multi(i32 %0, double %1)
 // WINDOWS-NEXT: ret void
 
-// LINUX: declare i32 @foo.arch_sandybridge()
+// LINUX: define i32 @fwd_decl_default()
+// LINUX: ret i32 2
+// LINUX: define i32 @fwd_decl_avx.avx()
+// LINUX: ret i32 2
+// LINUX: define i32 @fwd_decl_avx()
+// LINUX: ret i32 2
 
+// WINDOWS: define dso_local i32 @fwd_decl_default()
+// WINDOWS: ret i32 2
+// WINDOWS: define dso_local i32 @fwd_decl_avx.avx()
+// WINDOWS: ret i32 2
+// WINDOWS: define dso_local i32 @fwd_decl_avx()
+// WINDOWS: ret i32 2
+
+// LINUX: define void @bar5()
+// LINUX: call i32 @fwd_decl_default.ifunc()
+// LINUX: call i32 @fwd_decl_avx.ifunc()
+
+// WINDOWS: define dso_local void @bar5()
+// WINDOWS: call i32 @fwd_decl_default.resolver()
+// WINDOWS: call i32 @fwd_decl_avx.resolver()
+
+// LINUX: define i32 ()* @fwd_decl_default.resolver() comdat
+// LINUX: call void @__cpu_indicator_init()
+// LINUX: ret i32 ()* @fwd_decl_default
+// LINUX: define i32 ()* @fwd_decl_avx.resolver() comdat
+// LINUX: call void @__cpu_indicator_init()
+// LINUX: ret i32 ()* @fwd_decl_avx.avx
+// LINUX: ret i32 ()* @fwd_decl_avx
+
+// WINDOWS: define dso_local i32 @fwd_decl_default.resolver() comdat
+// WINDOWS: call void @__cpu_indicator_init()
+// WINDOWS: call i32 @fwd_decl_default
+// WINDOWS: define dso_local i32 @fwd_decl_avx.resolver() comdat
+// WINDOWS: call void @__cpu_indicator_init()
+// WINDOWS: call i32 @fwd_decl_avx.avx
+// WINDOWS: call i32 @fwd_decl_avx
+
+// LINUX: declare i32 @foo.arch_sandybridge()
 // WINDOWS: declare dso_local i32 @foo.arch_sandybridge()
 
 // LINUX: define linkonce i32 @foo_inline.sse4.2()
diff --git a/clang/test/Sema/attr-target-mv.c b/clang/test/Sema/attr-target-mv.c
index 671adff5b04..664ade1c0fa 100644
--- a/clang/test/Sema/attr-target-mv.c
+++ b/clang/test/Sema/attr-target-mv.c
@@ -65,10 +65,9 @@ int __attribute__((target("sse4.2,arch=sandybridge"))) mangle(void) { return 1;
 //expected-note@-2 {{previous declaration is here}}
 int __attribute__((target("arch=sandybridge,sse4.2")))  mangle(void) { return 2; }
 
+// allow this, since we want to treat the 1st one as fwd-decl of the sandybridge version.
 int prev_no_target(void);
 int __attribute__((target("arch=sandybridge")))  prev_no_target(void) { return 2; }
-// expected-error@-2 {{function declaration is missing 'target' attribute in a multiversioned function}}
-// expected-note@+1 {{function multiversioning caused by this declaration}}
 int __attribute__((target("arch=ivybridge")))  prev_no_target(void) { return 2; }
 
 int __attribute__((target("arch=sandybridge")))  prev_no_target2(void);