[clang] 954a729 - [clang][bytecode] Diagnose reading mutable fields in Memcpy op (#197197)

[via cfe-commits]

Author: Timm Baeder
Date: 2026-05-15T10:29:28+02:00
New Revision: 954a729039953b42af644a20f44707e86978b977

URL: https://github.com/llvm/llvm-project/commit/954a729039953b42af644a20f44707e86978b977
DIFF: https://github.com/llvm/llvm-project/commit/954a729039953b42af644a20f44707e86978b977.diff

LOG: [clang][bytecode] Diagnose reading mutable fields in Memcpy op (#197197)

Added: 
    

Modified: 
    clang/lib/AST/ByteCode/InterpBuiltin.cpp
    clang/test/AST/ByteCode/records.cpp

Removed: 
    


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diff  --git a/clang/lib/AST/ByteCode/InterpBuiltin.cpp b/clang/lib/AST/ByteCode/InterpBuiltin.cpp
index e05c9aed39b14..3e9ce902427eb 100644
--- a/clang/lib/AST/ByteCode/InterpBuiltin.cpp
+++ b/clang/lib/AST/ByteCode/InterpBuiltin.cpp
@@ -6664,15 +6664,17 @@ static bool copyRecord(InterpState &S, CodePtr OpPC, const Pointer &Src,
   assert(SrcDesc->ElemRecord == DestDesc->ElemRecord);
   const Record *R = DestDesc->ElemRecord;
   for (const Record::Field &F : R->fields()) {
+    Pointer FP = Src.atField(F.Offset);
+
+    if (!CheckMutable(S, OpPC, FP))
+      return false;
+
     if (R->isUnion()) {
       // For unions, only copy the active field. Zero all others.
-      const Pointer &SrcField = Src.atField(F.Offset);
-      if (SrcField.isActive()) {
+      if (FP.isActive()) {
         if (!copyField(F, /*Activate=*/true))
           return false;
       } else {
-        if (!CheckMutable(S, OpPC, Src.atField(F.Offset)))
-          return false;
         Pointer DestField = Dest.atField(F.Offset);
         zeroAll(DestField);
       }

diff  --git a/clang/test/AST/ByteCode/records.cpp b/clang/test/AST/ByteCode/records.cpp
index 20ead8cffdd99..b3f07c3cf007e 100644
--- a/clang/test/AST/ByteCode/records.cpp
+++ b/clang/test/AST/ByteCode/records.cpp
@@ -2011,3 +2011,13 @@ namespace RVOPtrIsExtern {
   }
   static_assert(test_all(), "");
 }
+
+namespace MutableInMemcpy {
+  union H {
+    mutable struct {} gx; // both-note {{declared here}}
+  };
+  constexpr H h1 = {};
+  constexpr H h2 = h1; // both-error {{must be initialized by a constant expression}} \
+                       // both-note {{read of mutable member 'gx' is not allowed in a constant expression}} \
+                       // both-note {{in call}}
+}