[SemaCXX] Unconfuse Clang when std::align_val_t is unscoped in C++03

[EricWF]

Summary

When -faligned-allocation is specified in C++03 libc++ defines std::align_val_t as an unscoped enumeration type (because Clang didn't provide scoped enumerations as an extension until 8.0).
Unfortunately Clang confuses the align_val_t overloads of delete with the sized deallocation overloads which aren't enabled. This caused Clang to call the aligned deallocation function as if it were the sized deallocation overload.

For example: https://godbolt.org/z/xXJELh

This patch fixes the confusion.

[EricWF]

Accepting. This is a good candidate for post-commit review.

lib/Sema/SemaExprCXX.cpp

UsualDeallocFnInfo(Sema &S, DeclAccessPair Found)
       unsigned NumBaseParams = 1;
       if (FD->isDestroyingOperatorDelete()) {
         Destroying = true;
         ++NumBaseParams;
       }
       if (FD->getNumParams() == NumBaseParams + 2)
         HasAlignValT = HasSizeT = true;
       else if (FD->getNumParams() == NumBaseParams + 1) {
-        HasSizeT = FD->getParamDecl(NumBaseParams)->getType()->isIntegerType();
-        HasAlignValT = !HasSizeT;
+        QualType ParamTy = FD->getParamDecl(NumBaseParams)->getType();
+        HasAlignValT = ParamTy->isAlignValT();
+        HasSizeT = !HasAlignValT && ParamTy->isIntegerType();
       }
 
       // In CUDA, determine how much we'd like / dislike to call this.
       if (S.getLangOpts().CUDA)
         if (auto *Caller = dyn_cast<FunctionDecl>(S.CurContext))
           CUDAPref = S.IdentifyCUDAPreference(Caller, FD);
     }
 

test/SemaCXX/cxx03-aligned-allocation-unscoped-enum.cpp

+// RUN: %clang_cc1 -std=c++03 %s -faligned-allocation \
+// RUN:   -emit-llvm -o - | FileCheck %s
+
+// Ensure Clang doesn't confuse std::align_val_t with the sized deallocation
+// parameter when the enum type is unscoped. Libc++ does this in C++03 in order
+// to support aligned allocation in that dialect.
+
+using size_t = __decltype(sizeof(0));
+
+namespace std {
+enum align_val_t { zero = size_t(0),
+                   max = size_t(-1) };
+}
+
+// CHECK-LABEL: define void @_Z1fPi(
+void f(int *p) {
+  // CHECK-NOT: call void @_ZdlPvSt11align_val_t(
+  // CHECK: call void @_ZdlPv(
+  // CHECK: ret void
+  delete p;
+}