[mlir] Relax restriction on name location parsing

[jpienaar]

Summary

We currently restrict parsing of location to not allow nameloc being
nested inside nameloc. This restriction may be historical as there
doesn't seem to be a reason for it anymore (locations like this can be
constructed in C++ and they print fine). Relax this restriction in the
parser to allow this nesting.

mlir/lib/Parser/LocationParser.cpp

if (consumeIf(Token::colon)) {
     loc = FileLineColLoc::get(ctx, str, line.getValue(), column.getValue());
     return success();
   }
 
   // Otherwise, this is a NameLoc.
 
   // Check for a child location.
   if (consumeIf(Token::l_paren)) {
-    auto childSourceLoc = getToken().getLoc();
-
     // Parse the child location.
     LocationAttr childLoc;
     if (parseLocationInstance(childLoc))
       return failure();
 
-    // The child must not be another NameLoc.
-    if (childLoc.isa<NameLoc>())
-      return emitError(childSourceLoc,
-                       "child of NameLoc cannot be another NameLoc");
     loc = NameLoc::get(StringAttr::get(ctx, str), childLoc);
 
     // Parse the closing ')'.
     if (parseToken(Token::r_paren,
                    "expected ')' after child location of NameLoc"))
       return failure();
   } else {
     loc = NameLoc::get(StringAttr::get(ctx, str));

mlir/test/IR/invalid-locations.mlir

 
 func @location_name_missing_r_paren() {
 ^bb:
   return loc("foo"(unknown]) // expected-error {{expected ')' after child location of NameLoc}}
 }
 
 // -----
 
-func @location_name_child_is_name() {
-^bb:
-  return loc("foo"("foo")) // expected-error {{child of NameLoc cannot be another NameLoc}}
-}
-
-// -----
-
 func @location_callsite_missing_l_paren() {
 ^bb:
   return loc(callsite unknown  // expected-error {{expected '(' in callsite location}}
 }
 
 // -----
 
 func @location_callsite_missing_callee() {

mlir/test/IR/locations.mlir

// CHECK-ALIAS-SAME: %arg1: i32 loc("cheetos"),
       %y: i32 loc("cheetos"),
 // CHECK-SAME: %arg2: i32 loc("out_of_line_location2")):
 // CHECK-ALIAS-SAME: %arg2: i32 loc("out_of_line_location2")):
       %z: i32 loc("out_of_line_location2")):
     %1 = arith.addi %x, %y : i32
     "foo.yield"(%1) : (i32) -> ()
   }) : () -> ()
 
+// CHECK-LABEL: func @location_name_child_is_name
+func @location_name_child_is_name() {
+  // CHECK: "foo"("foo")
+  return loc("foo"("foo"))
+}
+
 // CHECK-ALIAS: #[[LOC]] = loc("out_of_line_location")
 #loc = loc("out_of_line_location")