[clang] [clang][bytecode] Fix zero-init of first union member (PR #106962)

[Timm Baeder via cfe-commits]

https://github.com/tbaederr created https://github.com/llvm/llvm-project/pull/106962

... if done via a ImplicitValueInitExpr.
We were already doing this later in visitZeroRecordInitializer().

>From 3ca8c6c3408d78163c01d5ff95796fdc310b9b63 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Timm=20B=C3=A4der?= <tbaeder at redhat.com>
Date: Mon, 2 Sep 2024 11:48:49 +0200
Subject: [PATCH] [clang][bytecode] Fix zero-init of first union member

... if done via a ImplicitValueInitExpr.
We were already doing this later in visitZeroRecordInitializer().
---
 clang/lib/AST/ByteCode/Compiler.cpp       | 8 ++------
 clang/test/SemaObjC/non-trivial-c-union.m | 1 +
 2 files changed, 3 insertions(+), 6 deletions(-)

diff --git a/clang/lib/AST/ByteCode/Compiler.cpp b/clang/lib/AST/ByteCode/Compiler.cpp
index dced9ea3493732..d8b4a554574e0a 100644
--- a/clang/lib/AST/ByteCode/Compiler.cpp
+++ b/clang/lib/AST/ByteCode/Compiler.cpp
@@ -1235,12 +1235,6 @@ bool Compiler<Emitter>::VisitImplicitValueInitExpr(
     assert(RD);
     if (RD->isInvalidDecl())
       return false;
-    if (RD->isUnion()) {
-      // C++11 [dcl.init]p5: If T is a (possibly cv-qualified) union type, the
-      // object's first non-static named data member is zero-initialized
-      // FIXME
-      return false;
-    }
 
     if (const auto *CXXRD = dyn_cast<CXXRecordDecl>(RD);
         CXXRD && CXXRD->getNumVBases() > 0) {
@@ -3434,6 +3428,8 @@ bool Compiler<Emitter>::visitZeroRecordInitializer(const Record *R,
     if (!this->emitFinishInitPop(E))
       return false;
 
+    // C++11 [dcl.init]p5: If T is a (possibly cv-qualified) union type, the
+    // object's first non-static named data member is zero-initialized
     if (R->isUnion())
       break;
   }
diff --git a/clang/test/SemaObjC/non-trivial-c-union.m b/clang/test/SemaObjC/non-trivial-c-union.m
index 4c294764c430d8..34f1caad59df70 100644
--- a/clang/test/SemaObjC/non-trivial-c-union.m
+++ b/clang/test/SemaObjC/non-trivial-c-union.m
@@ -1,4 +1,5 @@
 // RUN: %clang_cc1 -fsyntax-only -fblocks -fobjc-arc -fobjc-runtime-has-weak -I %S/Inputs -verify %s
+// RUN: %clang_cc1 -fsyntax-only -fblocks -fobjc-arc -fobjc-runtime-has-weak -I %S/Inputs -verify -fexperimental-new-constant-interpreter %s
 
 #include "non-trivial-c-union.h"