Don't warn on returning the address of a label from a statement expression

Summary:
There isn't anything inherently wrong with returning a label from a
statement expression. In practice, the Linux kernel uses this pattern to
materialize PCs.

Fixes PR38569

Reviewers: niravd, rsmith, nickdesaulniers

Subscribers: cfe-commits

Differential Revision: https://reviews.llvm.org/D50805

llvm-svn: 340101

clang/lib/Sema/SemaInit.cpp

@@ -6924,6 +6924,10 @@ void Sema::checkInitializerLifetime(const InitializedEntity &Entity,
       } else if (isa<BlockExpr>(L)) {
         Diag(DiagLoc, diag::err_ret_local_block) << DiagRange;
       } else if (isa<AddrLabelExpr>(L)) {
+        // Don't warn when returning a label from a statement expression.
+        // Leaving the scope doesn't end its lifetime.
+        if (LK == LK_StmtExprResult)
+          return false;
         Diag(DiagLoc, diag::warn_ret_addr_label) << DiagRange;
       } else {
         Diag(DiagLoc, diag::warn_ret_local_temp_addr_ref)

clang/test/Sema/statements.c

@@ -34,6 +34,15 @@ bar:
   return &&bar;  // expected-warning {{returning address of label, which is local}}
 }
 
+// PR38569: Don't warn when returning a label from a statement expression.
+void test10_logpc(void*);
+void test10a() {
+  test10_logpc(({
+    my_pc:
+      &&my_pc;
+  }));
+}
+
 // PR6034
 void test11(int bit) {
   switch (bit)