[clang][AST] Propagate the value-dependent bit for VAArgExpr.

[hokein]

Summary

Fixes https://github.com/llvm/llvm-project/issues/62711

We never set the value-dependent bit for the VAArgExpr before this
patch, this was fine becase the dependent-type TypoExpr was always
resolved before checking the operands (see https://github.com/llvm/llvm-project/blob/main/clang/lib/Sema/SemaExpr.cpp#L21173-L21180)

Now we have enabled the dependence by default for C, the typo expr is
not early resolved before checking rather than delayed (share the same
codepath with C++).

The fix is to propagate the value-dependent bit for VAArgExpr where it contains
a TypoExpr, so that the AST node can be handled properly.

[aaron.ballman]

LGTM assuming CI is okay with it -- the patch did not apply so precommit CI never ran. I'm surprised no tests break as a result of this because it changes both C and C++ behavior. The changes should have a release note, too.

[hokein]

add release note

[hokein]

Thanks for the review.

In D150955#4356580, @aaron.ballman wrote:

LGTM assuming CI is okay with it -- the patch did not apply so precommit CI never ran. I'm surprised no tests break as a result of this because it changes both C and C++ behavior. The changes should have a release note, too.

This patch was based on my another fix (this probably explains why it failed to apply on pre-merge testing CI). I have test it with ninja check-clang.

clang/docs/ReleaseNotes.rst

- A default argument for a non-type template parameter is evaluated and checked
   (`#62596 <https://github.com/llvm/llvm-project/issues/62596>`_)
 - Fix an assertion when instantiating the body of a Class Template Specialization
   when it had been instantiated from a partial template specialization with different
   template arguments on the containing class. This fixes:
   (`#60778 <https://github.com/llvm/llvm-project/issues/60778>`_).
 - Fix a crash when an enum constant has a dependent-type recovery expression for
   C.
   (`#62446 <https://github.com/llvm/llvm-project/issues/62446>`_).
+- Propagate the value-dependent bit for VAArgExpr. Fixes a crash where a
+  __builtin_va_arg call has invalid arguments.
+  (`#62711 <https://github.com/llvm/llvm-project/issues/62711>`_).
 
 Bug Fixes to Compiler Builtins
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 Bug Fixes to Attribute Support
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 - Fixed a bug where attribute annotations on type specifiers (enums, classes,
   structs, unions, and scoped enums) were not properly ignored, resulting in

clang/lib/AST/ComputeDependence.cpp

for (auto *E : P->exprs())
     D |= E->getDependence();
   return D;
 }
 
 ExprDependence clang::computeDependence(VAArgExpr *E) {
   auto D = toExprDependenceAsWritten(
                E->getWrittenTypeInfo()->getType()->getDependence()) |
            (E->getSubExpr()->getDependence() & ~ExprDependence::Type);
-  return D & ~ExprDependence::Value;
+  return D;
 }
 
 ExprDependence clang::computeDependence(NoInitExpr *E) {
   return toExprDependenceForImpliedType(E->getType()->getDependence()) &
          (ExprDependence::Instantiation | ExprDependence::Error);
 }
 
 ExprDependence clang::computeDependence(ArrayInitLoopExpr *E) {

clang/test/AST/ast-dump-recovery.c

void test4() {
   enum GH62446 {
     // CHECK:      RecoveryExpr {{.*}} '<dependent type>' contains-errors lvalue
     // CHECK-NEXT: |-StringLiteral {{.*}} "a"
     // CHECK-NEXT: `-IntegerLiteral {{.*}} 2
     invalid_enum_value = "a" * 2,
     b,
   };
 }
+
+// Verify no crash
+void test5_GH62711() {
+  // CHECK:      VAArgExpr {{.*}} 'int' contains-errors
+  // CHECK-NEXT: | `-ImplicitCastExpr {{.*}} '<dependent type>' contains-errors
+  // CHECK-NEXT: |   `-RecoveryExpr {{.*}} '<dependent type>' contains-errors
+  if (__builtin_va_arg(undef, int) << 1);
+}