[CIR] Backport LValueBitcast for ComplexType (#1827)

Backport LValueBitcast support for ComplexType from the upstream

Author: AmrDeveloper

clang/lib/CIR/CodeGen/CIRGenExpr.cpp

@@ -1056,7 +1056,8 @@ LValue CIRGenFunction::emitDeclRefLValue(const DeclRefExpr *E) {
       cir::GlobalOp var = CGM.getOrCreateStaticVarDecl(
           *VD, CGM.getCIRLinkageVarDefinition(VD, /*IsConstant=*/false));
       auto getGlobalOp = builder.createGetGlobal(var);
-      auto actualElemTy = llvm::cast<cir::PointerType>(getGlobalOp.getType()).getPointee();
+      auto actualElemTy =
+          llvm::cast<cir::PointerType>(getGlobalOp.getType()).getPointee();
       addr = Address(getGlobalOp, actualElemTy, getContext().getDeclAlign(VD));
     } else {
       llvm_unreachable("DeclRefExpr for decl not entered in LocalDeclMap?");
@@ -2017,7 +2018,15 @@ LValue CIRGenFunction::emitCastLValue(const CastExpr *E) {
     assert(0 && "NYI");
   }
   case CK_LValueBitCast: {
-    assert(0 && "NYI");
+    // This must be a reinterpret_cast (or c-style equivalent).
+    const auto *ce = cast<ExplicitCastExpr>(E);
+
+    CGM.emitExplicitCastExprType(ce, this);
+    LValue LV = emitLValue(E->getSubExpr());
+    Address V = LV.getAddress().withElementType(
+        builder, convertTypeForMem(ce->getTypeAsWritten()->getPointeeType()));
+
+    return makeAddrLValue(V, E->getType(), LV.getBaseInfo(), LV.getTBAAInfo());
   }
   case CK_AddressSpaceConversion: {
     LValue LV = emitLValue(E->getSubExpr());

clang/lib/CIR/CodeGen/CIRGenExprComplex.cpp

@@ -444,8 +444,13 @@ mlir::Value ComplexExprEmitter::emitCast(CastKind CK, Expr *Op,
   case CK_UserDefinedConversion:
     llvm_unreachable("NYI");
 
-  case CK_LValueBitCast:
-    llvm_unreachable("NYI");
+  case CK_LValueBitCast: {
+    LValue origLV = CGF.emitLValue(Op);
+    Address addr =
+        origLV.getAddress().withElementType(Builder, CGF.convertType(DestTy));
+    LValue destLV = CGF.makeAddrLValue(addr, DestTy);
+    return emitLoadOfLValue(destLV, Op->getExprLoc());
+  }
 
   case CK_LValueToRValueBitCast: {
     LValue SourceLVal = CGF.emitLValue(Op);

clang/test/CIR/CodeGen/complex-cast.cpp

@@ -0,0 +1,21 @@
+// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -x c++ -fclangir -emit-cir -mmlir --mlir-print-ir-before=cir-canonicalize -o %t.cir %s 2>&1 | FileCheck --check-prefix=CIR-BEFORE %s
+// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -x c++ -fclangir -emit-cir -mmlir --mlir-print-ir-after=cir-canonicalize -o %t.cir %s 2>&1 | FileCheck --check-prefix=CIR-AFTER %s
+// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -fclangir -emit-llvm -o %t.ll %s
+// RUN: FileCheck --input-file=%t.ll --check-prefixes=LLVM %s
+
+struct CX {
+  double real;
+  double imag;
+};
+
+void complex_lvalue_bitcast() {
+  struct CX a;
+  (double _Complex &)a = {};
+}
+
+// CIR-BEFORE: %{{.*}} = cir.cast(bitcast, %{{.*}} : !cir.ptr<!rec_CX>), !cir.ptr<!cir.complex<!cir.double>>
+
+// CIR-AFTER: %{{.*}} = cir.cast(bitcast, %{{.*}} : !cir.ptr<!rec_CX>), !cir.ptr<!cir.complex<!cir.double>>
+
+// LLVM: %[[A_ADDR:.*]] = alloca %struct.CX, i64 1, align 8
+// LLVM: store { double, double } zeroinitializer, ptr %[[A_ADDR]], align 8