[clang][bytecode] Call CheckStore() before activating pointers (#165235)

We used to do this the other way around to work around an awkwardness
with CheckStore, namely that we shouldn't check pointers for being
activated when activating them.

Add a parameter to CheckStore instead and call CheckStore() _before_
activating and initializing the pointers in the respective opcode
implementations.

Fixes #164975

Author: tbaederr

clang/lib/AST/ByteCode/Interp.cpp

@@ -870,7 +870,8 @@ bool CheckFinalLoad(InterpState &S, CodePtr OpPC, const Pointer &Ptr) {
   return true;
 }
 
-bool CheckStore(InterpState &S, CodePtr OpPC, const Pointer &Ptr) {
+bool CheckStore(InterpState &S, CodePtr OpPC, const Pointer &Ptr,
+                bool WillBeActivated) {
   if (!Ptr.isBlockPointer() || Ptr.isZero())
     return false;
 
@@ -885,7 +886,7 @@ bool CheckStore(InterpState &S, CodePtr OpPC, const Pointer &Ptr) {
     return false;
   if (!CheckRange(S, OpPC, Ptr, AK_Assign))
     return false;
-  if (!CheckActive(S, OpPC, Ptr, AK_Assign))
+  if (!WillBeActivated && !CheckActive(S, OpPC, Ptr, AK_Assign))
     return false;
   if (!CheckGlobal(S, OpPC, Ptr))
     return false;

clang/lib/AST/ByteCode/Interp.h

@@ -75,7 +75,8 @@ bool CheckGlobalLoad(InterpState &S, CodePtr OpPC, const Block *B);
 bool CheckLocalLoad(InterpState &S, CodePtr OpPC, const Block *B);
 
 /// Checks if a value can be stored in a block.
-bool CheckStore(InterpState &S, CodePtr OpPC, const Pointer &Ptr);
+bool CheckStore(InterpState &S, CodePtr OpPC, const Pointer &Ptr,
+                bool WillBeActivated = false);
 
 /// Checks if a value can be initialized.
 bool CheckInit(InterpState &S, CodePtr OpPC, const Pointer &Ptr);
@@ -1977,13 +1978,12 @@ bool StoreActivate(InterpState &S, CodePtr OpPC) {
   const T &Value = S.Stk.pop<T>();
   const Pointer &Ptr = S.Stk.peek<Pointer>();
 
+  if (!CheckStore(S, OpPC, Ptr, /*WilLBeActivated=*/true))
+    return false;
   if (Ptr.canBeInitialized()) {
     Ptr.initialize();
     Ptr.activate();
   }
-
-  if (!CheckStore(S, OpPC, Ptr))
-    return false;
   Ptr.deref<T>() = Value;
   return true;
 }
@@ -1993,12 +1993,12 @@ bool StoreActivatePop(InterpState &S, CodePtr OpPC) {
   const T &Value = S.Stk.pop<T>();
   const Pointer &Ptr = S.Stk.pop<Pointer>();
 
+  if (!CheckStore(S, OpPC, Ptr, /*WilLBeActivated=*/true))
+    return false;
   if (Ptr.canBeInitialized()) {
     Ptr.initialize();
     Ptr.activate();
   }
-  if (!CheckStore(S, OpPC, Ptr))
-    return false;
   Ptr.deref<T>() = Value;
   return true;
 }
@@ -2007,7 +2007,8 @@ template <PrimType Name, class T = typename PrimConv<Name>::T>
 bool StoreBitField(InterpState &S, CodePtr OpPC) {
   const T &Value = S.Stk.pop<T>();
   const Pointer &Ptr = S.Stk.peek<Pointer>();
-  if (!CheckStore(S, OpPC, Ptr))
+
+  if (!CheckStore(S, OpPC, Ptr, /*WilLBeActivated=*/true))
     return false;
   if (Ptr.canBeInitialized())
     Ptr.initialize();
@@ -2037,12 +2038,13 @@ template <PrimType Name, class T = typename PrimConv<Name>::T>
 bool StoreBitFieldActivate(InterpState &S, CodePtr OpPC) {
   const T &Value = S.Stk.pop<T>();
   const Pointer &Ptr = S.Stk.peek<Pointer>();
+
+  if (!CheckStore(S, OpPC, Ptr, /*WilLBeActivated=*/true))
+    return false;
   if (Ptr.canBeInitialized()) {
     Ptr.initialize();
     Ptr.activate();
   }
-  if (!CheckStore(S, OpPC, Ptr))
-    return false;
   if (const auto *FD = Ptr.getField())
     Ptr.deref<T>() = Value.truncate(FD->getBitWidthValue());
   else
@@ -2055,12 +2057,12 @@ bool StoreBitFieldActivatePop(InterpState &S, CodePtr OpPC) {
   const T &Value = S.Stk.pop<T>();
   const Pointer &Ptr = S.Stk.pop<Pointer>();
 
+  if (!CheckStore(S, OpPC, Ptr, /*WillBeActivated=*/true))
+    return false;
   if (Ptr.canBeInitialized()) {
     Ptr.initialize();
     Ptr.activate();
   }
-  if (!CheckStore(S, OpPC, Ptr))
-    return false;
   if (const auto *FD = Ptr.getField())
     Ptr.deref<T>() = Value.truncate(FD->getBitWidthValue());
   else

clang/test/AST/ByteCode/unions.cpp

@@ -977,4 +977,13 @@ namespace UnionMemberOnePastEnd {
   }
   static_assert(!b());
 }
+
+namespace ActicvateInvalidPtr {
+  constexpr void bar() { // both-error {{never produces a constant expression}}
+    union {
+      int a[1];
+    } foo;
+    foo.a[1] = 0; // both-note {{assignment to dereferenced one-past-the-end pointer}}
+  }
+}
 #endif