Various bug fixes

[jgarzik]

No description provided.

[Copilot]

Pull request overview

This PR implements several bug fixes and new features for the C compiler, primarily focusing on GNU extensions and improved C99 compliance. The main additions are statement expressions (({ }) syntax), __builtin_offsetof/offsetof, and various builtin function recognitions, along with fixes for nested if-else CFG linking and enhanced error checking for bitfields, for-loop declarations, and variadic functions.

Key Changes:

• Added support for GNU statement expressions and __builtin_offsetof/offsetof
• Fixed nested if-else CFG linking issues in IR linearization
• Enhanced preprocessor to recognize additional builtins (__builtin_ctz*, __builtin_clz*, __builtin_popcount*) and report GNU extension support via __has_feature/__has_extension
• Added validation and warnings for empty enums, bitfield edge cases, for-loop storage class specifiers, and variadic functions without named parameters

Reviewed changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated 7 comments.

Show a summary per file

File	Description
cc/token/preprocess.rs	Added builtin function names (ctz, clz, popcount, offsetof, unreachable) and implemented __has_feature/__has_extension to report statement_expressions support
cc/parse/parser.rs	Implemented parsing for __builtin_offsetof, statement expressions, added for-loop init declaration validation, enhanced bitfield checks, and added warnings for empty enums and variadic functions
cc/parse/ast.rs	Added AST nodes for StmtExpr and OffsetOf expressions with supporting OffsetOfPath enum
cc/ir/linearize.rs	Fixed nested if-else CFG linking bug by tracking reachable blocks correctly; added linearization for OffsetOf and StmtExpr
cc/ir/test_linearize.rs	Added comprehensive tests for nested control flow, switch statements, loops, goto/labels, pointer arithmetic, floating-point operations, and new features
cc/tests/features/stmt_expr.rs	Added integration tests for statement expressions including basic usage, nested expressions, and control flow
cc/tests/features/offsetof.rs	Added integration tests for offsetof with basic structs, nested members, and array indexing
cc/tests/features/mod.rs	Added module declarations for new test files
cc/tests/features/has_feature.rs	Updated tests to verify __has_builtin(offsetof) and __has_feature(statement_expressions) return true
cc/doc/BUILTIN.md	Documented __builtin_offsetof and offsetof in the structure layout section