3e3eec090d
`bswap` is `0F C8+rd` — the register rides in the opcode's low three bits, like
`push`/`pop`/`xchg`/`mov`, but behind an escape byte. The decoder's retry at the
+r base opcode was gated on `esc == .NONE`, so only the register-0 forms
(`0F C8` = bswap eax, `48 0F C8` = bswap rax) landed on a table entry directly;
the other seven registers came back INVALID_OPCODE. Emission was always correct
— every `bswap` this compiler has ever produced runs — but a disassembly
containing one stopped dead, which is how it surfaced: three functions in
sigil's JIT corpus disassembled to a header with no instructions under it.
The table was never the problem. BSWAP is in `tablegen/encoding_table.odin` and
in the generated decode table, exactly where it should be.
Fixing the gate meant looking at why the retry existed twice. There is a correct
+r handler further down, carrying comments that describe two bugs already found
and fixed in it — "scan ALL entries, not just the first", "scan for the sized
register rather than assuming op0" — and the copy inside the retry had received
neither, plus a third of its own. So the retry now re-runs only the LOOKUP and
falls through to the single handler, which fixes two more instruction families
that were equally undecodable:
- `xchg rAX, r` (90+rd): 0x90's run sorts NOP ahead of XCHG, and the copy
tested only the first entry for a +r form, so every `xchg rAX, r` was
rejected.
- `push bx` / `pop bx` / `mov cx, imm` (any +r under 0x66): the copy passed
`prefix` where the legacy row wants 0, since for legacy opcodes 0x66 is
operand size rather than part of the opcode's identity.
Two supporting changes. The shared handler's default answer is now the first +r
entry rather than `idx.start`, so a fall-through at 0x90 cannot answer NOP for
an `xchg`. And a base-opcode retry that does not land on a +r form is now an
error rather than a fall-through: decoding 0x0E as the 0x08 entry (OR) would be
a wrong instruction reported confidently, which is worse than an unknown byte.
Verified three ways. Every opcode in every escape map was decoded before and
after: 154 combinations changed, every one of them INVALID -> valid, and nothing
that already decoded decodes differently. All 24 BSWAP encodings and all 96
legacy +r encodings were diffed against llvm-mc's disassembly and agree
operand-for-operand. Six new decode-only cases pin the three families; five of
them fail without this change.
(Two remaining differences from llvm-mc are deliberate and documented here:
implicit accumulators are left unmaterialized so a short form re-encodes to the
short form, and `48 90` reads as `xchg rax` rather than `nop`.)
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Riok9vMpkLmo78wsVKJHhz
The Data-Oriented Language for Sane Software Development.
The Odin Programming Language
Odin is a general-purpose programming language with distinct typing, built for high performance, modern systems, and built-in data-oriented data types. The Odin Programming Language, the C alternative for the joy of programming.
Website: https://odin-lang.org/
package main
import "core:fmt"
main :: proc() {
program := "+ + * 😃 - /"
accumulator := 0
for token in program {
switch token {
case '+': accumulator += 1
case '-': accumulator -= 1
case '*': accumulator *= 2
case '/': accumulator /= 2
case '😃': accumulator *= accumulator
case: // Ignore everything else
}
}
fmt.printf("The program \"%s\" calculates the value %d\n",
program, accumulator)
}
Documentation
Getting Started
Instructions for downloading and installing the Odin compiler and libraries.
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Overview of Odin
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- The Odin compiler is still in development.