P0188R1: add support for standard [[fallthrough]] attribute. This is almost

exactly the same as clang's existing [[clang::fallthrough]] attribute, which
has been updated to have the same semantics. The one significant difference
is that [[fallthrough]] is ill-formed if it's not used immediately before a
switch label (even when -Wimplicit-fallthrough is disabled). To support that,
we now build a CFG of any function that uses a '[[fallthrough]];' statement
to check.

In passing, fix some bugs with our support for statement attributes -- in
particular, diagnose their use on declarations, rather than asserting.

llvm-svn: 262881

1 files changed, 18 insertions, 4 deletions

diff --git a/clang/test/SemaCXX/switch-implicit-fallthrough.cpp b/clang/test/SemaCXX/switch-implicit-fallthrough.cpp
index 0bc43cdbd45..9540b1ff288 100644
--- a/clang/test/SemaCXX/switch-implicit-fallthrough.cpp
+++ b/clang/test/SemaCXX/switch-implicit-fallthrough.cpp
@@ -179,18 +179,15 @@ void fallthrough_cfgblock_with_null_successor(int x) {
 
 int fallthrough_position(int n) {
   switch (n) {
-      [[clang::fallthrough]];  // expected-warning{{fallthrough annotation does not directly precede switch label}}
       n += 300;
       [[clang::fallthrough]];  // expected-warning{{fallthrough annotation in unreachable code}}
     case 221:
-      [[clang::fallthrough]];  // expected-warning{{fallthrough annotation does not directly precede switch label}}
       return 1;
       [[clang::fallthrough]];  // expected-warning{{fallthrough annotation in unreachable code}}
     case 222:
-      [[clang::fallthrough]];  // expected-warning{{fallthrough annotation does not directly precede switch label}}
       n += 400;
     case 223:          // expected-warning{{unannotated fall-through between switch labels}} expected-note{{insert '[[clang::fallthrough]];' to silence this warning}} expected-note{{insert 'break;' to avoid fall-through}}
-      [[clang::fallthrough]]; // expected-warning{{fallthrough annotation does not directly precede switch label}}
+      ;
   }
 
   long p = static_cast<long>(n) * n;
@@ -282,6 +279,23 @@ namespace PR18983 {
   }
 }
 
+int fallthrough_placement_error(int n) {
+  switch (n) {
+      [[clang::fallthrough]]; // expected-warning{{fallthrough annotation in unreachable code}}
+      n += 300;
+    case 221:
+      [[clang::fallthrough]]; // expected-error{{fallthrough annotation does not directly precede switch label}}
+      return 1;
+    case 222:
+      [[clang::fallthrough]]; // expected-error{{fallthrough annotation does not directly precede switch label}}
+      n += 400;
+      [[clang::fallthrough]];
+    case 223:
+      [[clang::fallthrough]]; // expected-error{{fallthrough annotation does not directly precede switch label}}
+  }
+  return n;
+}
+
 int fallthrough_targets(int n) {
   [[clang::fallthrough]]; // expected-error{{fallthrough annotation is outside switch statement}}