[CIR] Backport ConstantExpr support for ScalarExpr (#2082)

Backport ConstantExpr support for ScalarExpr from the upstream with
tests also from Complex ConstantExpr

Author: AmrDeveloper

clang/lib/CIR/CodeGen/CIRGenExprScalar.cpp

@@ -155,7 +155,25 @@ class ScalarExprEmitter : public StmtVisitor<ScalarExprEmitter, mlir::Value> {
     return {};
   }
 
-  mlir::Value VisitConstantExpr(ConstantExpr *E) { llvm_unreachable("NYI"); }
+  mlir::Value VisitConstantExpr(ConstantExpr *E) {
+    // A constant expression of type 'void'
+    // generates no code and produces no value.
+    if (E->getType()->isVoidType())
+      return {};
+
+    if (mlir::Attribute result = ConstantEmitter(CGF).tryEmitConstantExpr(E)) {
+      if (E->isGLValue()) {
+        return {};
+      }
+
+      return Builder.getConstant(CGF.getLoc(E->getSourceRange()),
+                                 mlir::cast<mlir::TypedAttr>(result));
+    }
+
+    llvm_unreachable("ScalarExprEmitter: VisitConstantExpr");
+    return {};
+  }
+
   mlir::Value VisitParenExpr(ParenExpr *PE) { return Visit(PE->getSubExpr()); }
 
   mlir::Value VisitPackIndexingExpr(PackIndexingExpr *E) {

clang/test/CIR/CodeGen/constant-expr.cpp

@@ -0,0 +1,42 @@
+// RUN: %clang_cc1 -std=c++20 -triple x86_64-unknown-linux-gnu -Wno-unused-value -fclangir -emit-cir %s -o %t.cir
+// RUN: FileCheck --input-file=%t.cir %s -check-prefix=CIR
+// RUN: %clang_cc1 -std=c++20 -triple x86_64-unknown-linux-gnu -Wno-unused-value -fclangir -emit-llvm %s -o %t-cir.ll
+// RUN: FileCheck --input-file=%t-cir.ll %s -check-prefix=LLVM
+// RUN: %clang_cc1 -std=c++20 -triple x86_64-unknown-linux-gnu -Wno-unused-value -emit-llvm %s -o %t.ll
+// RUN: FileCheck --input-file=%t.ll %s -check-prefix=OGCG
+
+struct StructWithConstEval {
+  consteval int _Complex consteval_ret_complex() { return {1, 2}; }
+  consteval int consteval_ret_int() { return 1; }
+  consteval void consteval_ret_void() {}
+};
+
+void calling_consteval_methods() {
+  StructWithConstEval a;
+  int b = a.consteval_ret_int();
+  int _Complex c = a.consteval_ret_complex();
+  a.consteval_ret_void();
+}
+
+// CIR: %[[A_ADDR:.*]] = cir.alloca !rec_StructWithConstEval, !cir.ptr<!rec_StructWithConstEval>, ["a"]
+// CIR: %[[B_ADDR:.*]] = cir.alloca !s32i, !cir.ptr<!s32i>, ["b", init]
+// CIR: %[[C_ADDR:.*]] = cir.alloca !cir.complex<!s32i>, !cir.ptr<!cir.complex<!s32i>>, ["c", init]
+// CIR: %[[CONST_1:.*]] = cir.const #cir.int<1> : !s32i
+// CIR: cir.store {{.*}} %[[CONST_1]], %[[B_ADDR]] : !s32i, !cir.ptr<!s32i>
+// CIR: %[[CONST_COMPLEX:.*]] = cir.const #cir.complex<#cir.int<1> : !s32i, #cir.int<2> : !s32i> : !cir.complex<!s32i>
+// CIR: cir.store {{.*}} %[[CONST_COMPLEX]], %[[C_ADDR]] : !cir.complex<!s32i>, !cir.ptr<!cir.complex<!s32i>>
+
+// LLVM: %[[A_ADDR:.*]] = alloca %struct.StructWithConstEval, i64 1, align 1
+// LLVM: %[[B_ADDR:.*]] = alloca i32, i64 1, align 4
+// LLVM: %[[C_ADDR:.*]] = alloca { i32, i32 }, i64 1, align 4
+// LLVM: store i32 1, ptr %[[B_ADDR]], align 4
+// LLVM: store { i32, i32 } { i32 1, i32 2 }, ptr %[[C_ADDR]], align 4
+
+// OGCG: %[[A_ADDR:.*]] = alloca %struct.StructWithConstEval, align 1
+// OGCG: %[[B_ADDR:.*]] = alloca i32, align 4
+// OGCG: %[[C_ADDR:.*]] = alloca { i32, i32 }, align 4
+// OGCG: store i32 1, ptr %[[B_ADDR]], align 4
+// OGCG: %[[C_REAL_PTR:.*]] = getelementptr inbounds nuw { i32, i32 }, ptr %[[C_ADDR]], i32 0, i32 0
+// OGCG: %[[C_IMAG_PTR:.*]] = getelementptr inbounds nuw { i32, i32 }, ptr %[[C_ADDR]], i32 0, i32 1
+// OGCG: store i32 1, ptr %[[C_REAL_PTR]], align 4
+// OGCG: store i32 2, ptr %[[C_IMAG_PTR]], align 4