[mlir] Fix generate-test-checks.py: don't put attr refs in CHECK-LABEL (#188985)

Two related bugs in generate-test-checks.py when a top-level operation
carries attribute alias references (e.g. `#map`, `#map1`) in its
signature:

1. The attribute reference substitution (replacing `#map` with
`#[[$ATTR_0]]`) ran *before* the pending attribute definitions were
processed, so the names were not yet available and the references were
left as-is in the output.

2. CHECK-LABEL lines do not support FileCheck variable references (e.g.
`#[[$ATTR_0]]`), so even after substitution the generated check would be
syntactically wrong.

Fix both issues:
- In the CHECK-LABEL branch, re-apply `process_attribute_references` to
the label prefix and SSA-split rest after flushing pending attribute
definitions, so that names are resolved.
- Split the label prefix at attribute reference boundaries; keep only
the text before the first reference in the CHECK-LABEL line and emit the
remainder on a CHECK-SAME line.

Before:
// CHECK-LABEL: func.func @test() attributes {amap = #map, bmap = #map1}
{

After:
  // CHECK-LABEL:   func.func @test() attributes {amap =
  // CHECK-SAME:      #[[$ATTR_0]], bmap = #[[$ATTR_1]]} {

Fixes #162310

Assisted-by: Claude Code

mlir/utils/generate-test-checks.py

@@ -63,6 +63,11 @@ ATTR_RE = re.compile(ATTR_RE_STR)
 ATTR_DEF_RE_STR = r'\s*' + ATTR_RE_STR + r'\s*='
 ATTR_DEF_RE = re.compile(ATTR_DEF_RE_STR)
 
+# Regex matching a FileCheck attribute variable reference produced by this script,
+# e.g. #[[$ATTR_0]] or #[[$ATTR_0:.+]].  Used to detect references that cannot
+# appear in a CHECK-LABEL line (CHECK-LABEL does not support variable references).
+ATTR_REF_IN_LABEL_RE = re.compile(r"(#\[\[\$[^\]]*\]\])")
+
 
 # Class used to generate and manage string substitution blocks for SSA value
 # names.
@@ -446,26 +451,52 @@ def main():
             output_line += process_line(ssa_split[1:], variable_namer)
 
         else:
-            # Emit any pending attribute definitions at the start of this scope
+            # Emit any pending attribute definitions at the start of this scope.
+            # This must happen *before* re-processing the label line's attribute
+            # references below, so that names are available for substitution.
             for attr in pending_attr_defs:
                 attr_line = process_attribute_definition(attr, attribute_namer)
                 if attr_line:
                     output_segments[-1].append(attr_line)
             pending_attr_defs.clear()
 
-            # Output the first line chunk that does not contain an SSA name for the
-            # label.
-            output_line = "// " + args.check_prefix + "-LABEL: " + ssa_split[0] + "\n"
+            # Re-apply attribute reference substitution now that names have been
+            # generated by the pending attribute definitions above.  The first call
+            # at line 431 may have run before the names were defined.
+            label_prefix = process_attribute_references(ssa_split[0], attribute_namer)
+            ssa_rest = [
+                process_attribute_references(arg, attribute_namer)
+                for arg in ssa_split[1:]
+            ]
+
+            # CHECK-LABEL does not support FileCheck variable references such as
+            # #[[$ATTR_0]].  If the label prefix contains attribute references, split
+            # at the first one: keep only the text before it in the CHECK-LABEL line
+            # and move the remainder to a following CHECK-SAME line.
+            label_attr_parts = ATTR_REF_IN_LABEL_RE.split(label_prefix)
+
+            output_line = (
+                "// "
+                + args.check_prefix
+                + "-LABEL: "
+                + label_attr_parts[0].rstrip()
+                + "\n"
+            )
+
+            # Pad continuation lines to align with the end of the label prefix
+            # (capped at 20 chars to avoid excessive indentation).
+            label_length = len(label_attr_parts[0])
+            pad_depth = label_length if label_length < 21 else 4
+
+            # Emit any attribute references from the label prefix as CHECK-SAME.
+            if len(label_attr_parts) > 1:
+                output_line += "// " + args.check_prefix + "-SAME:  "
+                output_line += " " * pad_depth
+                output_line += "".join(label_attr_parts[1:]).rstrip() + "\n"
 
             # Process the rest of the input line on separate check lines.
-            for argument in ssa_split[1:]:
+            for argument in ssa_rest:
                 output_line += "// " + args.check_prefix + "-SAME:  "
-
-                # Pad to align with the original position in the line (i.e. where the label ends),
-                # unless the label is more than 20 chars long, in which case pad with 4 spaces
-                # (this is to avoid deep indentation).
-                label_length = len(ssa_split[0])
-                pad_depth = label_length if label_length < 21 else 4
                 output_line += " " * pad_depth
 
                 # Process the rest of the line. Use the original SSA name to generate the LIT