[clang] [clang][initlist] handle incomplete array type in Constant Expr Calculation (PR #155080)

[Congcong Cai via cfe-commits]

https://github.com/HerrCai0907 updated https://github.com/llvm/llvm-project/pull/155080

>From c0b28af40d2b9feaf388fdb841e80f6e70864192 Mon Sep 17 00:00:00 2001
From: Congcong Cai <congcongcai0907 at 163.com>
Date: Sat, 23 Aug 2025 14:05:04 +0800
Subject: [PATCH] [clang][initlist] handle incomplete array type in Constant
 Expr Calculation

In #65918, support of incomplete array type is added in TryReferenceListInitialization.
It causes the crash in Constant Expr Calculation since it only considers the case where it is ConstantArrayType.

This patch wants to add support for incomplete array type also.
---
 clang/lib/AST/ExprConstant.cpp                    | 12 ++++++++----
 clang/test/CodeGenCXX/cxx20-p0388-unbound-ary.cpp | 15 +++++++++++++++
 2 files changed, 23 insertions(+), 4 deletions(-)

diff --git a/clang/lib/AST/ExprConstant.cpp b/clang/lib/AST/ExprConstant.cpp
index 9b934753bcc3c..301fc64f3f84f 100644
--- a/clang/lib/AST/ExprConstant.cpp
+++ b/clang/lib/AST/ExprConstant.cpp
@@ -4030,9 +4030,13 @@ findSubobject(EvalInfo &Info, const Expr *E, const CompleteObject &Obj,
     if (ObjType->isArrayType()) {
       // Next subobject is an array element.
       const ConstantArrayType *CAT = Info.Ctx.getAsConstantArrayType(ObjType);
-      assert(CAT && "vla in literal type?");
+      const IncompleteArrayType *IAT =
+          Info.Ctx.getAsIncompleteArrayType(ObjType);
+      const ArrayType *AT = CAT ? static_cast<const ArrayType *>(CAT)
+                                : static_cast<const ArrayType *>(IAT);
+      assert(AT && "vla in literal type?");
       uint64_t Index = Sub.Entries[I].getAsArrayIndex();
-      if (CAT->getSize().ule(Index)) {
+      if (CAT && CAT->getSize().ule(Index)) {
         // Note, it should not be possible to form a pointer with a valid
         // designator which points more than one past the end of the array.
         if (Info.getLangOpts().CPlusPlus11)
@@ -4043,12 +4047,12 @@ findSubobject(EvalInfo &Info, const Expr *E, const CompleteObject &Obj,
         return handler.failed();
       }
 
-      ObjType = CAT->getElementType();
+      ObjType = AT->getElementType();
 
       if (O->getArrayInitializedElts() > Index)
         O = &O->getArrayInitializedElt(Index);
       else if (!isRead(handler.AccessKind)) {
-        if (!CheckArraySize(Info, CAT, E->getExprLoc()))
+        if (CAT && !CheckArraySize(Info, CAT, E->getExprLoc()))
           return handler.failed();
 
         expandArray(*O, Index);
diff --git a/clang/test/CodeGenCXX/cxx20-p0388-unbound-ary.cpp b/clang/test/CodeGenCXX/cxx20-p0388-unbound-ary.cpp
index a29f4d720c1de..007b47c441b2f 100644
--- a/clang/test/CodeGenCXX/cxx20-p0388-unbound-ary.cpp
+++ b/clang/test/CodeGenCXX/cxx20-p0388-unbound-ary.cpp
@@ -32,4 +32,19 @@ void foo(int a) {
   f({a});
 }
 
+constexpr int gh151716() {
+  int(&&g)[]{0,1,2};
+  return g[2];
+}
+// CHECK-LABEL: @_ZN3One10gh151716_fEv
+// CHECK-NEXT: entry:
+// CHECK-NEXT:   %v = alloca i32, align 4
+// CHECK-NEXT:   call void @llvm.lifetime.start.p0(ptr nonnull %v)
+// CHECK-NEXT:   store volatile i32 2, ptr %v, align 4
+// CHECK-NEXT:   call void @llvm.lifetime.end.p0(ptr nonnull %v)
+// CHECK-NEXT:   ret void
+void gh151716_f() {
+  volatile const int v = gh151716();
+}
+
 } // namespace One