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

[Timm Baeder via cfe-commits]

https://github.com/tbaederr created https://github.com/llvm/llvm-project/pull/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 https://github.com/llvm/llvm-project/issues/164975

>From 2b09df4d1a4171952966b76920a969f690517634 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Timm=20B=C3=A4der?= <tbaeder at redhat.com>
Date: Mon, 27 Oct 2025 11:52:03 +0100
Subject: [PATCH] [clang][bytecode] Call CheckStore() before activating
 pointers

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 https://github.com/llvm/llvm-project/issues/164975
---
 clang/lib/AST/ByteCode/Interp.cpp  |  5 +++--
 clang/lib/AST/ByteCode/Interp.h    | 24 +++++++++++++-----------
 clang/test/AST/ByteCode/unions.cpp |  9 +++++++++
 3 files changed, 25 insertions(+), 13 deletions(-)

diff --git a/clang/lib/AST/ByteCode/Interp.cpp b/clang/lib/AST/ByteCode/Interp.cpp
index 910868b27f48e..0e2ba3c5e82d2 100644
--- a/clang/lib/AST/ByteCode/Interp.cpp
+++ b/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;
diff --git a/clang/lib/AST/ByteCode/Interp.h b/clang/lib/AST/ByteCode/Interp.h
index 89f6fbefb1907..43c3ab76b15f9 100644
--- a/clang/lib/AST/ByteCode/Interp.h
+++ b/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
diff --git a/clang/test/AST/ByteCode/unions.cpp b/clang/test/AST/ByteCode/unions.cpp
index 6bccbda23f468..414070417a02a 100644
--- a/clang/test/AST/ByteCode/unions.cpp
+++ b/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