[clang] [clang][bytecode] Create temporary before discarding CXXConstructExpr (PR #154280)

[Timm Baeder via cfe-commits]

https://github.com/tbaederr created https://github.com/llvm/llvm-project/pull/154280

Fixes #154110

>From 5add943d38ac3a9b455fa3fcf7992e21138d5cd3 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Timm=20B=C3=A4der?= <tbaeder at redhat.com>
Date: Tue, 19 Aug 2025 09:52:05 +0200
Subject: [PATCH] [clang][bytecode] Create temporary before discarding
 CXXConstructExpr

Fixes #154110
---
 clang/lib/AST/ByteCode/Compiler.cpp | 14 +++++++-------
 clang/test/AST/ByteCode/cxx20.cpp   | 16 ++++++++++++++++
 clang/test/AST/ByteCode/records.cpp | 16 ++++++++--------
 3 files changed, 31 insertions(+), 15 deletions(-)

diff --git a/clang/lib/AST/ByteCode/Compiler.cpp b/clang/lib/AST/ByteCode/Compiler.cpp
index f2ce69a62838e..f7947bd8a3797 100644
--- a/clang/lib/AST/ByteCode/Compiler.cpp
+++ b/clang/lib/AST/ByteCode/Compiler.cpp
@@ -3181,13 +3181,6 @@ bool Compiler<Emitter>::VisitCXXConstructExpr(const CXXConstructExpr *E) {
   if (T->isRecordType()) {
     const CXXConstructorDecl *Ctor = E->getConstructor();
 
-    // Trivial copy/move constructor. Avoid copy.
-    if (Ctor->isDefaulted() && Ctor->isCopyOrMoveConstructor() &&
-        Ctor->isTrivial() &&
-        E->getArg(0)->isTemporaryObject(Ctx.getASTContext(),
-                                        T->getAsCXXRecordDecl()))
-      return this->visitInitializer(E->getArg(0));
-
     // If we're discarding a construct expression, we still need
     // to allocate a variable and call the constructor and destructor.
     if (DiscardResult) {
@@ -3203,6 +3196,13 @@ bool Compiler<Emitter>::VisitCXXConstructExpr(const CXXConstructExpr *E) {
         return false;
     }
 
+    // Trivial copy/move constructor. Avoid copy.
+    if (Ctor->isDefaulted() && Ctor->isCopyOrMoveConstructor() &&
+        Ctor->isTrivial() &&
+        E->getArg(0)->isTemporaryObject(Ctx.getASTContext(),
+                                        T->getAsCXXRecordDecl()))
+      return this->visitInitializer(E->getArg(0));
+
     // Zero initialization.
     if (E->requiresZeroInitialization()) {
       const Record *R = getRecord(E->getType());
diff --git a/clang/test/AST/ByteCode/cxx20.cpp b/clang/test/AST/ByteCode/cxx20.cpp
index cc315d36456d5..67bf9a732d8b7 100644
--- a/clang/test/AST/ByteCode/cxx20.cpp
+++ b/clang/test/AST/ByteCode/cxx20.cpp
@@ -1084,3 +1084,19 @@ namespace Virtual {
   static_assert(l.b == 10);
   static_assert(l.c == 10);
 }
+
+namespace DiscardedTrivialCXXConstructExpr {
+  struct S {
+    constexpr S(int a) : x(a) {}
+    int x;
+  };
+
+  constexpr int foo(int x) { // ref-error {{never produces a constant expression}}
+    throw S(3); // both-note {{not valid in a constant expression}} \
+                // ref-note {{not valid in a constant expression}}
+    return 1;
+  }
+
+  constexpr int y = foo(12); // both-error {{must be initialized by a constant expression}} \
+                             // both-note {{in call to}}
+}
diff --git a/clang/test/AST/ByteCode/records.cpp b/clang/test/AST/ByteCode/records.cpp
index 5ca3e2d12e2df..48cf81182c1de 100644
--- a/clang/test/AST/ByteCode/records.cpp
+++ b/clang/test/AST/ByteCode/records.cpp
@@ -1,11 +1,11 @@
-// RUN: %clang_cc1 -fexperimental-new-constant-interpreter -std=c++14 -verify=expected,both %s
-// RUN: %clang_cc1 -fexperimental-new-constant-interpreter -std=c++17 -verify=expected,both %s
-// RUN: %clang_cc1 -fexperimental-new-constant-interpreter -std=c++17 -triple i686 -verify=expected,both %s
-// RUN: %clang_cc1 -fexperimental-new-constant-interpreter -std=c++20 -verify=expected,both %s
-// RUN: %clang_cc1 -verify=ref,both -std=c++14 %s
-// RUN: %clang_cc1 -verify=ref,both -std=c++17 %s
-// RUN: %clang_cc1 -verify=ref,both -std=c++17 -triple i686 %s
-// RUN: %clang_cc1 -verify=ref,both -std=c++20 %s
+// RUN: %clang_cc1 -std=c++14 -verify=expected,both              %s -fexperimental-new-constant-interpreter
+// RUN: %clang_cc1 -std=c++17 -verify=expected,both              %s -fexperimental-new-constant-interpreter
+// RUN: %clang_cc1 -std=c++17 -verify=expected,both -triple i686 %s -fexperimental-new-constant-interpreter
+// RUN: %clang_cc1 -std=c++20 -verify=expected,both              %s -fexperimental-new-constant-interpreter
+// RUN: %clang_cc1 -std=c++14 -verify=ref,both                   %s
+// RUN: %clang_cc1 -std=c++17 -verify=ref,both                   %s
+// RUN: %clang_cc1 -std=c++17 -verify=ref,both -triple i686      %s
+// RUN: %clang_cc1 -std=c++20 -verify=ref,both                   %s
 
 /// Used to crash.
 struct Empty {};