[clang] 36b179d - [clang][Sema] Crash due to asm labeled incomplete global register decls (#219746)

[via cfe-commits]

Author: Oliver Hunt
Date: 2026-09-07T21:09:39Z
New Revision: 36b179dff5c85de0a7aca763e618d8c15dd5b2e7

URL: https://github.com/llvm/llvm-project/commit/36b179dff5c85de0a7aca763e618d8c15dd5b2e7
DIFF: https://github.com/llvm/llvm-project/commit/36b179dff5c85de0a7aca763e618d8c15dd5b2e7.diff

LOG: [clang][Sema] Crash due to asm labeled incomplete global register decls (#219746)

CheckAsmLabel fails to check for an incomplete type before attempting to
get the type layout. Short circuit on an incomplete type as Sema will
already reject a global with an incomplete type.

Added: 
    clang/test/Sema/global-explicit-register-undefined-type.c

Modified: 
    clang/docs/ReleaseNotes.md
    clang/lib/Sema/SemaDecl.cpp

Removed: 
    


################################################################################
diff  --git a/clang/docs/ReleaseNotes.md b/clang/docs/ReleaseNotes.md
index a49971adef86f..d57876b429de3 100644
--- a/clang/docs/ReleaseNotes.md
+++ b/clang/docs/ReleaseNotes.md
@@ -511,6 +511,7 @@ features cannot lower the translation-unit ABI level;
 - Fixed a crash when declaring a member template within a local class inside an OpenMP region. (#GH216052)
 - Fixed a bug where repeated #imports of modular headers in non-modular compilation were translated to #pragma clang module import. (#GH216924)
 - Fixed an assertion when `#pragma omp declare simd` or `#pragma omp declare variant` is followed by another OpenMP declarative directive containing a qualified identifier. (#GH217204)
+- Fixed a crash when an `asm` label names the register for a global variable of incomplete type. (#GH219746)
 
 #### Bug Fixes to Compiler Builtins
 

diff  --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index 2451baaf94703..a9047f61a8bf5 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -7760,6 +7760,8 @@ void Sema::CheckAsmLabel(Scope *S, Expr *E, StorageClass SC,
   StringLiteral *SE = cast<StringLiteral>(E);
   StringRef Label = SE->getString();
   QualType R = TInfo->getType();
+  if (R->isIncompleteType())
+    return;
   if (S->getFnParent() != nullptr) {
     switch (SC) {
     case SC_None:

diff  --git a/clang/test/Sema/global-explicit-register-undefined-type.c b/clang/test/Sema/global-explicit-register-undefined-type.c
new file mode 100644
index 0000000000000..83fab19b2deab
--- /dev/null
+++ b/clang/test/Sema/global-explicit-register-undefined-type.c
@@ -0,0 +1,9 @@
+// RUN: %clang_cc1 %s -triple arm64-apple-macosx -fsyntax-only -verify
+
+register struct Undefined1 bar1 asm("x1"); // #inline-type-def
+// expected-error@#inline-type-def {{tentative definition has type 'struct Undefined1' that is never completed}}
+// expected-note@#inline-type-def {{forward declaration of 'struct Undefined1'}}
+struct Undefined2; // #outline-type-def
+register struct Undefined2 bar2 asm("x1"); // #outline-type-label
+// expected-error@#outline-type-label {{tentative definition has type 'struct Undefined2' that is never completed}}
+// expected-note@#outline-type-def {{forward declaration of 'struct Undefined2'}}