[CIR][Transforms] Add folding for addrspace cast

Author: seven-mile

clang/lib/CIR/Dialect/IR/CIRDialect.cpp

@@ -523,7 +523,8 @@ OpFoldResult CastOp::fold(FoldAdaptor adaptor) {
       return foldResults[0].get<mlir::Attribute>();
     return {};
   }
-  case mlir::cir::CastKind::bitcast: {
+  case mlir::cir::CastKind::bitcast:
+  case mlir::cir::CastKind::address_space: {
     return getSrc();
   }
   default:

clang/test/CIR/Transforms/merge-cleanups.cir

@@ -126,4 +126,13 @@ module  {
     cir.return %0 : !cir.ptr<!s32i>
   }
 
+  // Should remove redundant address space casts.
+  // CHECK-LABEL: @addrspacecastfold
+  //       CHECK:  %[[ARG0:.+]]: !cir.ptr<!s32i, addrspace(2)>
+  //       CHECK:  cir.return %[[ARG0]] : !cir.ptr<!s32i, addrspace(2)>
+  cir.func @addrspacecastfold(%arg0: !cir.ptr<!s32i, addrspace(2)>) -> !cir.ptr<!s32i, addrspace(2)> {
+    %0 = cir.cast(address_space, %arg0: !cir.ptr<!s32i, addrspace(2)>), !cir.ptr<!s32i, addrspace(2)>
+    cir.return %0 : !cir.ptr<!s32i, addrspace(2)>
+  }
+
 }