[Clang] [C2y] Implement N3355 ‘Named Loops’ (#152870)

This implements support for [named
loops](https://www.open-std.org/jtc1/sc22/wg14/www/docs/n3355.htm) for
C2y. 

When parsing a `LabelStmt`, we create the `LabeDecl` early before we parse 
the substatement; this label is then passed down to `ParseWhileStatement()` 
and friends, which then store it in the loop’s (or switch statement’s) `Scope`; 
when we encounter a `break/continue` statement, we perform a lookup for 
the label (and error if it doesn’t exist), and then walk the scope stack and 
check if there is a scope whose preceding label is the target label, which 
identifies the jump target.

The feature is only supported in C2y mode, though a cc1-only option
exists for testing (`-fnamed-loops`), which is mostly intended to try
and make sure that we don’t have to refactor this entire implementation
when/if we start supporting it in C++.

---------

Co-authored-by: Balazs Benics <benicsbalazs@gmail.com>

1 files changed, 2 insertions, 4 deletions

diff --git a/clang/lib/Tooling/Syntax/BuildTree.cpp b/clang/lib/Tooling/Syntax/BuildTree.cpp
index 546161c..b75f8ff 100644
--- a/clang/lib/Tooling/Syntax/BuildTree.cpp
+++ b/clang/lib/Tooling/Syntax/BuildTree.cpp
@@ -1482,16 +1482,14 @@ public:
   }
 
   bool WalkUpFromContinueStmt(ContinueStmt *S) {
-    Builder.markChildToken(S->getContinueLoc(),
-                           syntax::NodeRole::IntroducerKeyword);
+    Builder.markChildToken(S->getKwLoc(), syntax::NodeRole::IntroducerKeyword);
     Builder.foldNode(Builder.getStmtRange(S),
                      new (allocator()) syntax::ContinueStatement, S);
     return true;
   }
 
   bool WalkUpFromBreakStmt(BreakStmt *S) {
-    Builder.markChildToken(S->getBreakLoc(),
-                           syntax::NodeRole::IntroducerKeyword);
+    Builder.markChildToken(S->getKwLoc(), syntax::NodeRole::IntroducerKeyword);
     Builder.foldNode(Builder.getStmtRange(S),
                      new (allocator()) syntax::BreakStatement, S);
     return true;