[clang] [CIR] Implement GenericSelectionExpr for AggregateExpr (PR #161003)

[Amr Hesham via cfe-commits]

https://github.com/AmrDeveloper created https://github.com/llvm/llvm-project/pull/161003

Implement the GenericSelectionExpr for AggregateExpr

>From 3cb7afa9b05c6d821fbe05cab2697929217f685c Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=E2=80=9CAmr?= <amr96 at programmer.net>
Date: Sat, 27 Sep 2025 13:00:12 +0200
Subject: [PATCH] [CIR] Implement GenericSelectionExpr for AggregateExpr

---
 clang/lib/CIR/CodeGen/CIRGenExprAggregate.cpp |  3 +-
 clang/lib/CIR/CodeGen/CIRGenFunction.cpp      |  2 ++
 clang/test/CIR/CodeGen/struct.cpp             | 28 +++++++++++++++++++
 3 files changed, 31 insertions(+), 2 deletions(-)

diff --git a/clang/lib/CIR/CodeGen/CIRGenExprAggregate.cpp b/clang/lib/CIR/CodeGen/CIRGenExprAggregate.cpp
index 4a8aac900ee07..1ac3b106556ec 100644
--- a/clang/lib/CIR/CodeGen/CIRGenExprAggregate.cpp
+++ b/clang/lib/CIR/CodeGen/CIRGenExprAggregate.cpp
@@ -135,8 +135,7 @@ class AggExprEmitter : public StmtVisitor<AggExprEmitter> {
     cgf.cgm.errorNYI(pe->getSourceRange(), "AggExprEmitter: VisitParenExpr");
   }
   void VisitGenericSelectionExpr(GenericSelectionExpr *ge) {
-    cgf.cgm.errorNYI(ge->getSourceRange(),
-                     "AggExprEmitter: VisitGenericSelectionExpr");
+    Visit(ge->getResultExpr());
   }
   void VisitCoawaitExpr(CoawaitExpr *e) {
     cgf.cgm.errorNYI(e->getSourceRange(), "AggExprEmitter: VisitCoawaitExpr");
diff --git a/clang/lib/CIR/CodeGen/CIRGenFunction.cpp b/clang/lib/CIR/CodeGen/CIRGenFunction.cpp
index 0abb21a670719..41f9f26f00577 100644
--- a/clang/lib/CIR/CodeGen/CIRGenFunction.cpp
+++ b/clang/lib/CIR/CodeGen/CIRGenFunction.cpp
@@ -832,6 +832,8 @@ LValue CIRGenFunction::emitLValue(const Expr *e) {
     return emitCallExprLValue(cast<CallExpr>(e));
   case Expr::ParenExprClass:
     return emitLValue(cast<ParenExpr>(e)->getSubExpr());
+  case Expr::GenericSelectionExprClass:
+    return emitLValue(cast<GenericSelectionExpr>(e)->getResultExpr());
   case Expr::DeclRefExprClass:
     return emitDeclRefLValue(cast<DeclRefExpr>(e));
   case Expr::CStyleCastExprClass:
diff --git a/clang/test/CIR/CodeGen/struct.cpp b/clang/test/CIR/CodeGen/struct.cpp
index ee6c4cab7341f..8d2e9df6a2d8b 100644
--- a/clang/test/CIR/CodeGen/struct.cpp
+++ b/clang/test/CIR/CodeGen/struct.cpp
@@ -93,3 +93,31 @@ void f3() {
 // OGCG:   %[[O:.*]] = alloca %struct.Outer, align 4
 // OGCG:   %[[O_I:.*]] = getelementptr inbounds nuw %struct.Outer, ptr %[[O]], i32 0, i32 0
 // OGCG:   %[[O_I_N:.*]] = getelementptr inbounds nuw %struct.Inner, ptr %[[O_I]], i32 0, i32 0
+
+void generic_selection() {
+  CompleteS a;
+  CompleteS b;
+  int c;
+  CompleteS d = _Generic(c, int : a, default: b);
+}
+
+// CIR: cir.func{{.*}} @_Z17generic_selectionv()
+// CIR:   %[[A_ADDR:.*]] = cir.alloca !rec_CompleteS, !cir.ptr<!rec_CompleteS>, ["a"]
+// CIR:   %[[B_ADDR:.*]] = cir.alloca !rec_CompleteS, !cir.ptr<!rec_CompleteS>, ["b"]
+// CIR:   %[[C_ADDR:.*]] = cir.alloca !s32i, !cir.ptr<!s32i>, ["c"]
+// CIR:   %[[D_ADDR:.*]] = cir.alloca !rec_CompleteS, !cir.ptr<!rec_CompleteS>, ["d", init]
+// CIR:   cir.call @_ZN9CompleteSC1ERKS_(%[[D_ADDR]], %[[A_ADDR]]) nothrow : (!cir.ptr<!rec_CompleteS>, !cir.ptr<!rec_CompleteS>) -> ()
+
+// LLVM: define{{.*}} void @_Z17generic_selectionv()
+// LLVM:   %1 = alloca %struct.CompleteS, i64 1, align 4
+// LLVM:   %2 = alloca %struct.CompleteS, i64 1, align 4
+// LLVM:   %3 = alloca i32, i64 1, align 4
+// LLVM:   %4 = alloca %struct.CompleteS, i64 1, align 4
+// LLVM:   call void @_ZN9CompleteSC1ERKS_(ptr %4, ptr %1)
+
+// OGCG: define{{.*}} void @_Z17generic_selectionv()
+// OGCG:   %[[A_ADDR:.*]] = alloca %struct.CompleteS, align 4
+// OGCG:   %[[B_ADDR:.*]] = alloca %struct.CompleteS, align 4
+// OGCG:   %[[C_ADDR:.*]] = alloca i32, align 4
+// OGCG:   %[[D_ADDR:.*]] = alloca %struct.CompleteS, align 4
+// OGCG:   call void @llvm.memcpy.p0.p0.i64(ptr align 4 %[[D_ADDR]], ptr align 4 %[[A_ADDR]], i64 8, i1 false)