[clang] [clang][ExprConst] Support DesignatedInitUpdateExpr of array type (PR #201000)

[Timm Baeder via cfe-commits]

https://github.com/tbaederr created https://github.com/llvm/llvm-project/pull/201000

I think this should work.

>From 0f7f733e99bc102cb3bf19da074cfae3ef0959d6 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Timm=20B=C3=A4der?= <tbaeder at redhat.com>
Date: Tue, 2 Jun 2026 06:09:28 +0200
Subject: [PATCH] [clang][ExprConst] Support DesignatedInitUpdateExpr of array
 type

I think this should work.
---
 clang/lib/AST/ByteCode/Compiler.cpp | 1 -
 clang/lib/AST/ExprConstant.cpp      | 8 ++++++++
 clang/test/Sema/constexpr.c         | 8 ++++++++
 3 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/clang/lib/AST/ByteCode/Compiler.cpp b/clang/lib/AST/ByteCode/Compiler.cpp
index 732a9e227430c..7b5b6ce368dca 100644
--- a/clang/lib/AST/ByteCode/Compiler.cpp
+++ b/clang/lib/AST/ByteCode/Compiler.cpp
@@ -7834,7 +7834,6 @@ bool Compiler<Emitter>::VisitDeclRefExpr(const DeclRefExpr *E) {
 template <class Emitter>
 bool Compiler<Emitter>::VisitDesignatedInitUpdateExpr(
     const DesignatedInitUpdateExpr *E) {
-  assert(E->getType()->isRecordType());
   if (!this->visitInitializer(E->getBase()))
     return false;
   return this->visitInitializer(E->getUpdater());
diff --git a/clang/lib/AST/ExprConstant.cpp b/clang/lib/AST/ExprConstant.cpp
index 7601d68b13939..f78854d15a9f2 100644
--- a/clang/lib/AST/ExprConstant.cpp
+++ b/clang/lib/AST/ExprConstant.cpp
@@ -15024,6 +15024,7 @@ namespace {
                                          ArrayRef<Expr *> Args,
                                          const Expr *ArrayFiller,
                                          QualType AllocType = QualType());
+    bool VisitDesignatedInitUpdateExpr(const DesignatedInitUpdateExpr *E);
   };
 } // end anonymous namespace
 
@@ -15411,6 +15412,13 @@ bool ArrayExprEvaluator::VisitCXXParenListInitExpr(
                                          E->getArrayFiller());
 }
 
+bool ArrayExprEvaluator::VisitDesignatedInitUpdateExpr(
+    const DesignatedInitUpdateExpr *E) {
+  if (!Visit(E->getBase()))
+    return false;
+  return Visit(E->getUpdater());
+}
+
 //===----------------------------------------------------------------------===//
 // Integer Evaluation
 //
diff --git a/clang/test/Sema/constexpr.c b/clang/test/Sema/constexpr.c
index cf029446bd362..51ee62d2495f3 100644
--- a/clang/test/Sema/constexpr.c
+++ b/clang/test/Sema/constexpr.c
@@ -446,3 +446,11 @@ static_assert(designated_init_b.a.d == 12.0); // expected-warning {{folding it t
 static_assert(designated_init_b.a.e[0] == 5); // expected-warning {{folding it to a constant is a GNU extension}}
 static_assert(designated_init_b.a.e[1] == 13); // expected-warning {{folding it to a constant is a GNU extension}}
 static_assert(designated_init_b.y == 14);
+
+struct S2 {
+  char L[4];
+  int M;
+};
+const struct S2 s2[2] = {{{"foo"}, 1}, [0].L[2] = 'x'}; // expected-warning {{initializer partially overrides prior initialization of this subobject}} \
+                                                        // expected-note {{previous initialization is here}}
+static_assert(s2[0].L[2] == 'x');// expected-warning {{folding it to a constant is a GNU extension}}