Allow casts like (char*)&b + 1 to passthrough for non-constexpr const initialization

Author: chaitanyav

clang/lib/AST/ByteCode/InterpBuiltin.cpp

@@ -2176,7 +2176,7 @@ static bool interp__builtin_assume_dereferenceable(InterpState &S, CodePtr OpPC,
                                                    const CallExpr *Call) {
   assert(Call->getNumArgs() == 2);
 
-  APSInt ReqSize = popToAPSInt(S.Stk, *S.Ctx.classify(Call->getArg(1)));
+  APSInt ReqSize = popToAPSInt(S, Call->getArg(1));
   const Pointer &Ptr = S.Stk.pop<Pointer>();
 
   if (ReqSize.isZero())
@@ -2186,7 +2186,12 @@ static bool interp__builtin_assume_dereferenceable(InterpState &S, CodePtr OpPC,
         << AK_Read << S.Current->getRange(OpPC);
     return false;
   }
-  if (!Ptr.isLive() || !Ptr.isBlockPointer())
+  if (!Ptr.isBlockPointer()) {
+    if (Ptr.isIntegralPointer())
+      return true;
+    return false;
+  }
+  if (!Ptr.isLive())
     return false;
   if (Ptr.isPastEnd()) {
     S.FFDiag(S.Current->getSource(OpPC), diag::note_constexpr_access_past_end)

clang/lib/AST/ExprConstant.cpp

@@ -19701,8 +19701,11 @@ class VoidExprEvaluator
         return true;
 
       LValue Pointer;
-      if (!EvaluatePointer(E->getArg(0), Pointer, Info))
+      if (!EvaluatePointer(E->getArg(0), Pointer, Info)) {
+        if (EvaluateBuiltinConstantP(Info, E->getArg(0)))
+          return true;
         return false;
+      }
       if (Pointer.Designator.Invalid)
         return false;
       if (Pointer.isNullPointer()) {

clang/test/SemaCXX/builtin-assume-dereferenceable-constexpr.cpp

@@ -90,3 +90,24 @@ constexpr int arr2[5] = {1, 2, 3, 4, 5};
 constexpr int too_large = (__builtin_assume_dereferenceable(arr2, 6 * sizeof(int)), 12); // expected-error {{constexpr variable 'too_large' must be initialized by a constant expression}} expected-note {{read of dereferenced one-past-the-end pointer is not allowed in a constant expression}}
 
 constexpr int null = (__builtin_assume_dereferenceable(nullptr, 4), 12); // expected-error {{constexpr variable 'null' must be initialized by a constant expression}} expected-note {{read of dereferenced null pointer is not allowed in a constant expression}}
+
+int b = 10;
+const int f = (__builtin_assume_dereferenceable((char*)&b + 1, 3), 12);
+int a = f;
+
+int c[10] = {};
+const int g = (__builtin_assume_dereferenceable((unsigned char*)c + 5, 35), 42);
+int d = g;
+
+long long ll = 100;
+const int h = (__builtin_assume_dereferenceable((void*)&ll, 8), 99);
+int e = h;
+
+struct Foo { int x; int y; int z; };
+Foo foo = {1, 2, 3};
+const int i = (__builtin_assume_dereferenceable((short*)&foo + 2, 8), 77);
+int j = i;
+
+double darr[10] = {};
+const int k = (__builtin_assume_dereferenceable((int*)darr, 40), 55);
+int l = k;