[mlir] Add support for broader range of input files in generate-test-checks.py (#134327)

A few additions:

- Lines with `{{`: These can show up if serializing non-MLIR info into
string attrs `my.attr = {{proto}, {...}}`. String escape the opening
`{{`, given that check lines are generated this has no effect on
`{{.*}}` etc in generated lines.
- File split line: Normally these are skipped because of their indent
level, but if using `--starts_from_scope=0` to generate checks for the
`module {...} {` line, and since MLIR opt tools emit file split lines by
default, some `CHECK: // -----` lines were emit.
- (edit removed this, fixed by
https://github.com/llvm/llvm-project/pull/134364) AttrAliases: I'm not
sure if I'm missing something for the attribute parser to work
correctly, but I was getting many `#[[?]]` for all dialect attrs. Only
use the attr aliasing if there's a match.

mlir/utils/generate-test-checks.py

@@ -236,9 +236,13 @@ def process_attribute_references(line, attribute_namer):
 # Pre-process a line of input to remove any character sequences that will be
 # problematic with FileCheck.
 def preprocess_line(line):
+    # Replace any `{{` with escaped replacements. `{{` corresponds to regex
+    # checks in FileCheck.
+    output_line = line.replace("{{", "{{\\{\\{}}")
+
     # Replace any double brackets, '[[' with escaped replacements. '[['
     # corresponds to variable names in FileCheck.
-    output_line = line.replace("[[", "{{\\[\\[}}")
+    output_line = output_line.replace("[[", "{{\\[\\[}}")
 
     # Replace any single brackets that are followed by an SSA identifier, the
     # identifier will be replace by a variable; Creating the same situation as
@@ -327,6 +331,11 @@ def main():
         if not input_line:
             continue
 
+        # When using `--starts_from_scope=0` to capture module lines, the file
+        # split needs to be skipped, otherwise a `CHECK: // -----` is inserted.
+        if input_line.startswith("// -----"):
+            continue
+
         # Check if this is an attribute definition and process it
         process_attribute_definition(input_line, attribute_namer, output)