i386 text-assembler (EmitAsm386) for cleaner x86-32 codegen

• Type: feature
• Status: done
• Owner: Antigravity
• Depends-on: feature-array-of-const (DONE), feature-asm-text-emitter (x86-64 core + shared asmtext.inc helpers, DONE)
• Opened: 2026-06-14

Motivation

ir_codegen386.inc is 2947 lines, ~970 of them raw EmitB($..) with the mnemonic only in a trailing comment, plus 57 manual CodeLen/Patch32 jump sites. Unreadable and the exact shape that produced the 19 DB vs 19 D3 ModRM bug — a class of bug the encode-ModRM-once text assembler cannot make. This is the highest-leverage conversion: biggest file, hottest backend, and it feeds the i386 self-host arc (current wall: Expected: unit miscompile — [[project_i386_selfhost_arc]]).

Why first / cheapest

EmitAsm386 shares the x86 ModRM/SIB core already written for EmitAsmX64 in compiler/asmtext.inc. i386 is the same encoder with REX dropped and the register set narrowed to eax..edi/esp/ebp (no r8..r15, no RIP-relative). Mostly a 32-bit entry point over the existing x86 layer, not new ISA work.

Scope (incremental — mix freely with EmitB)

1. EmitAsm386(const items: array of const) + single-line overload, over the shared x86 core. Registers 8/16/32-bit (al/ax/eax …), [base±disp], immediates; markers % (width inferred), @data/@glob (via EmitDataRef/ EmitGlobRef), .label: with rel8/rel32 back+forward resolution — the mechanism that deletes the 57 manual jump sites.
2. Grow the mnemonic table on demand — start with exactly what the converted blocks use (mov push pop add sub and or xor cmp lea inc dec + jmp/jcc
   • int 0x80/ret/leave).
3. Convert EmitwriteUInt64_386 (fixed body + a backward-jump loop + two @data) and at least one bound site (the IR_LOAD_SYM [ebp+disp] path). Leave heavily-dynamic blocks on EmitB/typed encoders.

Landmines

• Byte-identity discipline: converting a block shifts the emitted compiler's bytes, fine as long as the i386 fixedpoint cmp stays clean (native↔self both run the new assembler). Re-run after each conversion batch.
• PXX self-host: no short-circuit and/or + EMPTY-AnsiString index = nil deref → route conditional char reads through AsmTextCharAt; never reassign a var AnsiString param; keep scratch label tables module-global. (Already paid for in asmtext.inc; reuse those helpers, don't re-hit.) [[project_pxx_and_not_shortcircuit]] / [[project_pxx_array_of_const_selfhost]].

Acceptance

• EmitAsm386 with the marker/label/binding rules + single-line overload.
• EmitwriteUInt64_386 and ≥1 bound site converted; output correct.
• make test + make test-i386 green; i386 self-fixedpoint byte-identical.
• A focused test/test_asm_emit_386.pas against known-good bytes (imm/disp/label/reloc).

Deferred

Full ir_codegen386.inc conversion (incremental, on demand); retargeting the user asm … end path (asmenc.inc) onto the shared engine (own follow-up).

Log

• 2026-06-14 — opened. Mirrors the EmitAsmX64/EmitAsmXtensa work; first of the three remaining target emitters (386 → aarch64 → arm32). Shares the x86 core in asmtext.inc; primary payoff is the 970-EmitB/57-jump cleanup and the i386 self-host arc.
• 2026-06-14 — Claimed by Antigravity.
• 2026-06-14 — Completed. EmitAsm386 implemented, EmitwriteUInt64_386 and bound local/param loads converted. Verified via standalone test test/test_asm_emit_386.pas and compiler bootstrap. Commit: c8da1613a2df2cfbf4aa4e88cab33012bbc751d2.