[mlir] Update generic op ebnf to include region

[jpienaar]

Summary

Optional regions are supported in the generic op print/parse form, update the docs to match.

[merge_guards_bot]

Unit tests: unknown.

clang-tidy: pass.

clang-format: fail. Please format your changes with clang-format by running git-clang-format HEAD^ or applying this patch.

Build artifacts: clang-tidy.txt, clang-format.patch, CMakeCache.txt, console-log.txt

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[rriddle]

Can you also add the successor list? Full form is something like:

string-literal `(` ssa-use-list? `)` successor-list? (`(` region-list `)`)? attribute-dict? `:` function-type

mlir/docs/LangRef.md

 
 ## Operations
 
 Syntax:
 
 ```
 operation         ::= op-result-list? (generic-operation | custom-operation)
                       trailing-location?
-generic-operation ::= string-literal '(' ssa-use-list? ')' attribute-dict?
-                      `:` function-type
+generic-operation ::= string-literal `(` ssa-use-list? `)`  successor-list?
+                      (`(` region-list `)`)? attribute-dict? `:` function-type
 custom-operation  ::= bare-id custom-operation-format
 op-result-list    ::= op-result (`,` op-result)* `=`
 op-result         ::= ssa-id (`:` integer-literal)
 successor-list    ::= successor (`,` successor)*
 successor         ::= caret-id (`:` bb-arg-list)?
 region-list       ::= region (`,` region)*
 trailing-location ::= (`loc` `(` location `)`)?
 ```

mlir/lib/Parser/Parser.cpp

 // Operation Parsing
 //===----------------------------------------------------------------------===//
 
 /// Parse an operation.
 ///
 ///  operation         ::= op-result-list?
 ///                        (generic-operation | custom-operation)
 ///                        trailing-location?
-///  generic-operation ::= string-literal '(' ssa-use-list? ')' attribute-dict?
-///                        `:` function-type
+///  generic-operation ::= string-literal `(` ssa-use-list? `)`
+///                        successor-list? (`(` region-list `)`)?
+///                        attribute-dict? `:` function-type
 ///  custom-operation  ::= bare-id custom-operation-format
 ///  op-result-list    ::= op-result (`,` op-result)* `=`
 ///  op-result         ::= ssa-id (`:` integer-literal)
 ///
 ParseResult OperationParser::parseOperation() {
   auto loc = getToken().getLoc();
   SmallVector<std::tuple<StringRef, unsigned, SMLoc>, 1> resultIDs;
   size_t numExpectedResults = 0;