[clang][Interp] Fix a designated initializer testcase

This protected GetPtrField and ArrayDecay ops from dummy pointers
which fixes the attached test case for designated initializers in C.

Author: tbaederr

clang/lib/AST/Interp/Interp.h

@@ -1187,15 +1187,18 @@ inline bool GetPtrGlobal(InterpState &S, CodePtr OpPC, uint32_t I) {
 /// 2) Pushes Pointer.atField(Off) on the stack
 inline bool GetPtrField(InterpState &S, CodePtr OpPC, uint32_t Off) {
   const Pointer &Ptr = S.Stk.pop<Pointer>();
+
   if (S.inConstantContext() && !CheckNull(S, OpPC, Ptr, CSK_Field))
     return false;
-  if (!CheckExtern(S, OpPC, Ptr))
-    return false;
-  if (!CheckRange(S, OpPC, Ptr, CSK_Field))
-    return false;
-  if (!CheckSubobject(S, OpPC, Ptr, CSK_Field))
-    return false;
 
+  if (CheckDummy(S, OpPC, Ptr)) {
+    if (!CheckExtern(S, OpPC, Ptr))
+      return false;
+    if (!CheckRange(S, OpPC, Ptr, CSK_Field))
+      return false;
+    if (!CheckSubobject(S, OpPC, Ptr, CSK_Field))
+      return false;
+  }
   S.Stk.push<Pointer>(Ptr.atField(Off));
   return true;
 }
@@ -1896,8 +1899,10 @@ inline bool ArrayElemPop(InterpState &S, CodePtr OpPC, uint32_t Index) {
 inline bool ArrayDecay(InterpState &S, CodePtr OpPC) {
   const Pointer &Ptr = S.Stk.pop<Pointer>();
 
-  if (Ptr.isDummy())
-    return false;
+  if (Ptr.isDummy()) {
+    S.Stk.push<Pointer>(Ptr);
+    return true;
+  }
 
   if (!Ptr.isUnknownSizeArray()) {
     S.Stk.push<Pointer>(Ptr.atIndex(0));

clang/lib/AST/Interp/Pointer.cpp

@@ -99,7 +99,7 @@ APValue Pointer::toAPValue() const {
   else
     llvm_unreachable("Invalid allocation type");
 
-  if (isUnknownSizeArray() || Desc->asExpr())
+  if (isDummy() || isUnknownSizeArray() || Desc->asExpr())
     return APValue(Base, CharUnits::Zero(), Path, false, false);
 
   // TODO: compute the offset into the object.

clang/test/AST/Interp/c.c

@@ -112,3 +112,15 @@ _Static_assert(sizeof(name2) == 0, ""); // expected-error {{failed}} \
 #ifdef __SIZEOF_INT128__
 void *PR28739d = &(&PR28739d)[(__int128)(unsigned long)-1]; // all-warning {{refers past the last possible element}}
 #endif
+
+extern float global_float;
+struct XX { int a, *b; };
+struct XY { int before; struct XX xx, *xp; float* after; } xy[] = {
+  0, 0, &xy[0].xx.a, &xy[0].xx, &global_float,
+  [1].xx = 0, &xy[1].xx.a, &xy[1].xx, &global_float,
+  0,              // all-note {{previous initialization is here}}
+  0,              // all-note {{previous initialization is here}}
+  [2].before = 0, // all-warning {{initializer overrides prior initialization of this subobject}}
+  0,              // all-warning {{initializer overrides prior initialization of this subobject}}
+  &xy[2].xx.a, &xy[2].xx, &global_float
+};