[CIR][CodeGen] Support side effects in address space casting (llvm#673)

Continue the work of llvm#652 . Test the branch of null pointer expressions
with side effects.

Author: seven-mile

clang/lib/CIR/CodeGen/CIRGenExprScalar.cpp

@@ -1522,9 +1522,8 @@ mlir::Value ScalarExprEmitter::VisitCastExpr(CastExpr *CE) {
       // If E has side effect, it is emitted even if its final result is a
       // null pointer. In that case, a DCE pass should be able to
       // eliminate the useless instructions emitted during translating E.
-      if (Result.HasSideEffects) {
-        llvm_unreachable("NYI");
-      }
+      if (Result.HasSideEffects)
+        Visit(E);
       return CGF.CGM.buildNullConstant(DestTy, CGF.getLoc(E->getExprLoc()));
     }
     // Since target may map different address spaces in AST to the same address

clang/test/CIR/CodeGen/address-space-conversion.cpp

@@ -55,3 +55,14 @@ void test_nullptr() {
   // LLVM:      store ptr addrspace(1) null, ptr %{{[0-9]+}}, align 8
   // LLVM-NEXT: store ptr addrspace(2) null, ptr %{{[0-9]+}}, align 8
 }
+
+void test_side_effect(pi1_t b) {
+  pi2_t p = (pi2_t)(*b++, (int*)0);
+  // CIR:      %{{[0-9]+}} = cir.ptr_stride(%{{[0-9]+}} : !cir.ptr<!s32i, addrspace(1)>, %{{[0-9]+}} : !s32i), !cir.ptr<!s32i, addrspace(1)>
+  // CIR:      %[[#CAST:]] = cir.const #cir.ptr<null> : !cir.ptr<!s32i, addrspace(2)>
+  // CIR-NEXT: cir.store %[[#CAST]], %{{[0-9]+}} : !cir.ptr<!s32i, addrspace(2)>, !cir.ptr<!cir.ptr<!s32i, addrspace(2)>>
+
+  // LLVM:      %{{[0-9]+}} = getelementptr i32, ptr addrspace(1) %{{[0-9]+}}, i64 1
+  // LLVM:      store ptr addrspace(2) null, ptr %{{[0-9]+}}, align 8
+
+}