Motiejus Jakštys
b992036987
Add core Sema analysis infrastructure:
- InstMap operations: ensureSpaceForBody, get, put
- resolveInst: maps ZIR refs to AIR refs (pre-interned + inst_map)
- addAirInst: appends AIR instructions with auto-growth
- SemaBlock helpers: init, deinit, blockAddInst
- zirDbgStmt handler with comptime elision and coalescing
Implement analyzeBodyInner dispatch loop handling:
- dbg_stmt, break_inline, ret_implicit, extended (stub),
block_inline (recursive body analysis), declaration (skip)
- Default case maps unhandled instructions to void_type
Update semaAnalyze to set up root block, verify ZIR instruction 0
is struct_decl, exercise dispatch infrastructure, and transfer AIR
array ownership to returned Air struct.
Add smoke test for "fn foo() void {}" declarations.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
About
zig0 aspires to be an interpreter of zig 0.15.2 written in C.
This is written with help from LLM:
- Lexer:
- Datastructures 100% human.
- Helper functions 100% human.
- Lexing functions 50/50 human/bot.
- Parser:
- Datastructures 100% human.
- Helper functions 50/50.
- Parser functions 5/95 human/bot.
- AstGen: TBD.
Testing
Quick test:
./zig3 build fmt-zig0 test-zig0
Full test and static analysis with all supported compilers and valgrind (run before commit, takes a while):
./zig3 build all-zig0 -Dvalgrind
Debugging tips
Test runs infinitely? Build the test program executable:
$ ./zig3 build test-zig0 -Dzig0-no-exec
And then run it, capturing the stack trace:
gdb -batch \
-ex "python import threading; threading.Timer(1.0, lambda: gdb.post_event(lambda: gdb.execute('interrupt'))).start()" \
-ex run \
-ex "bt full" \
-ex quit \
zig-out/bin/test
You are welcome to replace -ex "bt full" with anything other of interest.
Float handling
Float literals are parsed with strtold() (C11 standard, portable). On
x86-64 Linux, long double is 80-bit extended precision (63 fraction bits).
When a float doesn't round-trip through f64, it's emitted as f128 (ZIR
float128 instruction). The 80-bit extended value is converted to IEEE 754
binary128 encoding by bit manipulation — both formats share the same 15-bit
exponent with bias 16383. The top 63 of binary128's 112 fraction bits come
from the 80-bit value; the bottom 49 are zero-padded.
This means float128 literals lose ~49 bits of precision compared to the
upstream Zig implementation (which uses native f128). This is acceptable
because stage0 is a bootstrap tool — the real Zig compiler re-parses all
source with full f128 precision in later stages. The test comparison mask
in astgen_test.zig skips float128 payloads to account for this.
Previous approach used __float128/strtof128 (GCC/glibc extensions) for
full precision, but these are not portable to TCC and other C11 compilers.