[clang] [clang][bytecode] Allow const mutation in all variable initializers (PR #195794)

[Timm Baeder via cfe-commits]

https://github.com/tbaederr updated https://github.com/llvm/llvm-project/pull/195794

>From 709a6c65db93d277337cf7b59c0cfd38251cb902 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Timm=20B=C3=A4der?= <tbaeder at redhat.com>
Date: Tue, 5 May 2026 07:39:17 +0200
Subject: [PATCH] [clang][bytecode]

---
 clang/lib/AST/ByteCode/Compiler.cpp |  6 ++++++
 clang/lib/AST/ByteCode/Interp.h     | 11 +++++++++++
 clang/lib/AST/ByteCode/Opcodes.td   |  4 ++++
 clang/test/AST/ByteCode/cxx14.cpp   | 12 ++++++++++++
 4 files changed, 33 insertions(+)

diff --git a/clang/lib/AST/ByteCode/Compiler.cpp b/clang/lib/AST/ByteCode/Compiler.cpp
index 11c5478a5c748..90f89c3e5af38 100644
--- a/clang/lib/AST/ByteCode/Compiler.cpp
+++ b/clang/lib/AST/ByteCode/Compiler.cpp
@@ -5290,9 +5290,15 @@ VarCreationState Compiler<Emitter>::visitVarDecl(const VarDecl *VD,
     if (!this->emitGetPtrGlobal(*GlobalIndex, Init))
       return false;
 
+    if (!this->emitStartInit(Init))
+      return false;
+
     if (!visitInitializer(Init))
       return false;
 
+    if (!this->emitEndInit(Init))
+      return false;
+
     return this->emitFinishInitGlobal(Init);
   }
   // Local variables.
diff --git a/clang/lib/AST/ByteCode/Interp.h b/clang/lib/AST/ByteCode/Interp.h
index 4a550fdd63bfb..fe2d99901d367 100644
--- a/clang/lib/AST/ByteCode/Interp.h
+++ b/clang/lib/AST/ByteCode/Interp.h
@@ -3564,6 +3564,17 @@ inline bool StartSpeculation(InterpState &S, CodePtr OpPC) {
   return true;
 }
 
+inline bool StartInit(InterpState &S, CodePtr OpPC) {
+  const Pointer &Ptr = S.Stk.peek<Pointer>();
+  S.InitializingBlocks.push_back(Ptr.block());
+  return true;
+}
+
+inline bool EndInit(InterpState &S, CodePtr OpPC) {
+  S.InitializingBlocks.pop_back();
+  return true;
+}
+
 // This is special-cased in the tablegen opcode emitter.
 // Its dispatch function will NOT call InterpNext
 // and instead simply return true.
diff --git a/clang/lib/AST/ByteCode/Opcodes.td b/clang/lib/AST/ByteCode/Opcodes.td
index 3fb25a5fa0884..57ed71fb6f16b 100644
--- a/clang/lib/AST/ByteCode/Opcodes.td
+++ b/clang/lib/AST/ByteCode/Opcodes.td
@@ -181,6 +181,10 @@ def Jf : JumpOpcode;
 def PushIgnoreDiags : Opcode;
 def PopIgnoreDiags : Opcode;
 
+
+def StartInit : Opcode;
+def EndInit : Opcode;
+
 def StartSpeculation : Opcode;
 def EndSpeculation : Opcode;
 def BCP : Opcode {
diff --git a/clang/test/AST/ByteCode/cxx14.cpp b/clang/test/AST/ByteCode/cxx14.cpp
index 00a9cf5b00098..170bd09504993 100644
--- a/clang/test/AST/ByteCode/cxx14.cpp
+++ b/clang/test/AST/ByteCode/cxx14.cpp
@@ -35,3 +35,15 @@ constexpr bool f() { // both-error {{constexpr function never produces a constan
                     // both-warning {{array index 3 is past the end of the array}}
   return true;
 }
+
+namespace InitListModify {
+  struct Aggregate {
+    int x = 0;
+    int y = ++x;
+  };
+  constexpr Aggregate aggr1;
+  static_assert(aggr1.x == 1 && aggr1.y == 1, "");
+  // FIXME: This is not specified by the standard, but sanity requires it.
+  constexpr Aggregate aggr2 = {};
+  static_assert(aggr2.x == 1 && aggr2.y == 1, "");
+}