[mlir] Align LLVM_Type ODS constraint on type verifiers

Verify only the outer type being LLVM-compatible, the elemental types if
present are already checked by the type verifiers. This makes some LLVM dialect
operations compatible with mixed-dialect types that appear during progressive
lowering.

Reviewed By: wsmoses

Differential Revision: https://reviews.llvm.org/D116671

mlir/include/mlir/Dialect/LLVMIR/LLVMOpBase.td

@@ -57,7 +57,7 @@ def LLVM_Dialect : Dialect {
 
 // LLVM dialect type.
 def LLVM_Type : DialectType<LLVM_Dialect,
-                            CPred<"::mlir::LLVM::isCompatibleType($_self)">,
+                            CPred<"::mlir::LLVM::isCompatibleOuterType($_self)">,
                             "LLVM dialect-compatible type">;
 
 // Type constraint accepting LLVM token type.

mlir/test/Dialect/LLVMIR/types.mlir

@@ -178,9 +178,11 @@ func @verbose() {
 
 // CHECK-LABEL: @ptr_elem_interface
 // CHECK-COUNT-3: !llvm.ptr<!test.smpla>
+// CHECK: llvm.mlir.undef : !llvm.ptr<!test.smpla>
 func @ptr_elem_interface(%arg0: !llvm.ptr<!test.smpla>) {
   %0 = llvm.load %arg0 : !llvm.ptr<!test.smpla>
   llvm.store %0, %arg0 : !llvm.ptr<!test.smpla>
+  llvm.mlir.undef : !llvm.ptr<!test.smpla>
   return
 }