[clang] [CodeGen] Remove the check that allowed non-POD compound literals to be directly evaluated into the destination even when it might alias the source (PR #167344)

[Akira Hatanaka via cfe-commits]

https://github.com/ahatanak created https://github.com/llvm/llvm-project/pull/167344

Evaluate all aggregate compound literals into a temporary and then copy it to the destination if aliasing is possible.

This fixes a latent issue exposed by #154490, where evaluating the RHS directly into the destination could ignore potential aliasing.

rdar://164094548

>From c381519885ec6c5ca34822488f16632498fa358b Mon Sep 17 00:00:00 2001
From: Akira Hatanaka <ahatanak at gmail.com>
Date: Sun, 9 Nov 2025 09:35:45 -0800
Subject: [PATCH] [CodeGen] Remove the check that allowed non-POD compound
 literals to be directly evaluated into the destination even when it might
 alias the source

Evaluate all aggregate compound literals into a temporary and then copy
it to the destination if aliasing is possible.

This fixes a latent issue exposed by #154490, where evaluating the RHS
directly into the destination could ignore potential aliasing.

rdar://164094548
---
 clang/lib/CodeGen/CGExprAgg.cpp              |  7 +--
 clang/test/CodeGenObjC/nontrivial-c-struct.m | 59 ++++++++++++++++++++
 2 files changed, 62 insertions(+), 4 deletions(-)
 create mode 100644 clang/test/CodeGenObjC/nontrivial-c-struct.m

diff --git a/clang/lib/CodeGen/CGExprAgg.cpp b/clang/lib/CodeGen/CGExprAgg.cpp
index eee397f1f3d19..4e61a6f61948f 100644
--- a/clang/lib/CodeGen/CGExprAgg.cpp
+++ b/clang/lib/CodeGen/CGExprAgg.cpp
@@ -755,10 +755,9 @@ void AggExprEmitter::VisitOpaqueValueExpr(OpaqueValueExpr *e) {
 
 void
 AggExprEmitter::VisitCompoundLiteralExpr(CompoundLiteralExpr *E) {
-  if (Dest.isPotentiallyAliased() &&
-      E->getType().isPODType(CGF.getContext())) {
-    // For a POD type, just emit a load of the lvalue + a copy, because our
-    // compound literal might alias the destination.
+  if (Dest.isPotentiallyAliased()) {
+    // Just emit a load of the lvalue + a copy, because our compound literal
+    // might alias the destination.
     EmitAggLoadOfLValue(E);
     return;
   }
diff --git a/clang/test/CodeGenObjC/nontrivial-c-struct.m b/clang/test/CodeGenObjC/nontrivial-c-struct.m
new file mode 100644
index 0000000000000..fa4fa223bc2d9
--- /dev/null
+++ b/clang/test/CodeGenObjC/nontrivial-c-struct.m
@@ -0,0 +1,59 @@
+// RUN: %clang_cc1 -triple arm64e-apple-ios18 -fptrauth-calls -fptrauth-intrinsics -fobjc-arc -emit-llvm -o - %s | FileCheck %s
+
+// CHECK: %[[STRUCT_S0:.*]] = type { i32, i32, ptr }
+// CHECK: %[[STRUCT_S1:.*]] = type { ptr, ptr }
+
+// This struct isn't POD because it has an address-discriminated ptrauth
+// field.
+typedef struct {
+  int f0, f1;
+  int * __ptrauth(1,1,50) f2;
+} S0;
+
+// This struct isn't POD because it has an address-discriminated ptrauth
+// field and an ARC ObjC pointer field.
+typedef struct {
+  id f0;
+  int * __ptrauth(1,1,50) f1;
+} S1;
+
+// CHECK: define void @compound_literal_assignment0(ptr noundef %[[P:.*]])
+// CHECK: %[[P_ADDR:.*]] = alloca ptr, align 8
+// CHECK-NEXT: %[[_COMPOUNDLITERAL:.*]] = alloca %[[STRUCT_S0]], align 8
+// CHECK-NEXT: store ptr %[[P]], ptr %[[P_ADDR]], align 8
+// CHECK-NEXT: %[[V0:.*]] = load ptr, ptr %[[P_ADDR]], align 8
+// CHECK-NEXT: %[[F0:.*]] = getelementptr inbounds nuw %[[STRUCT_S0]], ptr %[[_COMPOUNDLITERAL]], i32 0, i32 0
+// CHECK-NEXT: %[[V1:.*]] = load ptr, ptr %[[P_ADDR]], align 8
+// CHECK-NEXT: %[[F1:.*]] = getelementptr inbounds nuw %[[STRUCT_S0]], ptr %[[V1]], i32 0, i32 1
+// CHECK-NEXT: %[[V2:.*]] = load i32, ptr %[[F1]], align 4
+// CHECK-NEXT: store i32 %[[V2]], ptr %[[F0]], align 8
+// CHECK-NEXT: %[[F11:.*]] = getelementptr inbounds nuw %[[STRUCT_S0]], ptr %[[_COMPOUNDLITERAL]], i32 0, i32 1
+// CHECK-NEXT: %[[V3:.*]] = load ptr, ptr %[[P_ADDR]], align 8
+// CHECK-NEXT: %[[F02:.*]] = getelementptr inbounds nuw %[[STRUCT_S0]], ptr %[[V3]], i32 0, i32 0
+// CHECK-NEXT: %[[V4:.*]] = load i32, ptr %[[F02]], align 8
+// CHECK-NEXT: store i32 %[[V4]], ptr %[[F11]], align 4
+// CHECK-NEXT: %[[F2:.*]] = getelementptr inbounds nuw %[[STRUCT_S0]], ptr %[[_COMPOUNDLITERAL]], i32 0, i32 2
+// CHECK-NEXT: store ptr null, ptr %[[F2]], align 8
+// CHECK-NEXT: call void @__copy_assignment_8_8_t0w8_pa1_50_8(ptr %[[V0]], ptr %[[_COMPOUNDLITERAL]])
+// CHECK-NEXT: ret void
+
+void compound_literal_assignment0(S0 *p) {
+  *p = (S0){.f0 = p->f1, .f1 = p->f0};
+}
+
+// CHECK: define void @compound_literal_assignment1(ptr noundef %[[P:.*]])
+// CHECK: %[[P_ADDR:.*]] = alloca ptr, align 8
+// CHECK-NEXT: %[[_COMPOUNDLITERAL:.*]] = alloca %[[STRUCT_S1]], align 8
+// CHECK-NEXT: store ptr %[[P]], ptr %[[P_ADDR]], align 8
+// CHECK-NEXT: %[[V0:.*]] = load ptr, ptr %[[P_ADDR]], align 8
+// CHECK-NEXT: %[[F0:.*]] = getelementptr inbounds nuw %[[STRUCT_S1]], ptr %[[_COMPOUNDLITERAL]], i32 0, i32 0
+// CHECK-NEXT: store ptr null, ptr %[[F0]], align 8
+// CHECK-NEXT: %[[F1:.*]] = getelementptr inbounds nuw %[[STRUCT_S1]], ptr %[[_COMPOUNDLITERAL]], i32 0, i32 1
+// CHECK-NEXT: store ptr null, ptr %[[F1]], align 8
+// CHECK-NEXT: call void @__copy_assignment_8_8_s0_pa1_50_8(ptr %[[V0]], ptr %[[_COMPOUNDLITERAL]])
+// CHECK-NEXT: call void @__destructor_8_s0(ptr %[[_COMPOUNDLITERAL]])
+// CHECK-NEXT: ret void
+
+void compound_literal_assignment1(S1 *p) {
+  *p = (S1){};
+}