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fix(disasm): PPCBUG-640+650 fmt_bc spurious condition suffix on bdnz/bdz

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PPCBUG-640: For BO=16 (bdnz: decrement CTR, branch if non-zero, ignore CR)
and BO=18 (bdz: same with branch-if-zero), `fmt_bc` fell through to the
`if decr` block and computed `cond_name_opt` from the don't-care BI=0 /
cond_true=false pair, yielding `Some("ge")`. The output was therefore
`bdnzge` / `bdzge` — a CTR-only branch with a spurious CR-derived suffix.

PPCBUG-650 (companion): the golden fixture pinned the wrong output, so
the regression had no detection signal until now.

`fmt_bclr` already had the correct `if decr && uncond` guard at line 872
producing `bdnzlr` / `bdzlr`. `fmt_bc` lacked the equivalent.

Fix: gate the condition string on `!uncond` inside the `if decr` block.
For BO=16/18 (uncond bit set), the condition suffix is now empty.

Tests: extended_mnemonics.json fixture rows for bdnz/bdz now expect the
correct `ext_mnemonic: "bdnz"` / `"bdz"`.

Impact: every analysis-DB query for `bdnz` loops (common in pixel-shader
and vertex processing) was returning zero rows; matches stored as `bdnzge`.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
This commit is contained in:
MechaCat02
2026-05-02 10:40:45 +02:00
parent 3d8e2ced2e
commit d4f6ea787b
2 changed files with 6 additions and 3 deletions
Download Patch File Download Diff File Expand all files Collapse all files

5
crates/xenia-cpu/src/disasm.rs
View File

@@ -828,7 +828,10 @@ fn fmt_bc(instr: &DecodedInstr) -> DisasmText {
if decr { if decr {
let z = if bo & 0x02 != 0 { "z" } else { "nz" }; let z = if bo & 0x02 != 0 { "z" } else { "nz" };
let cond_str = cond_name_opt.unwrap_or(""); // BO bit 4 (uncond) means CR is ignored — pure CTR-decrement branch.
// Without this guard, bdnz/bdz would emit a spurious `ge` suffix derived
// from the don't-care BI=0 / cond_true=false pair (PPCBUG-640).
let cond_str = if uncond { "" } else { cond_name_opt.unwrap_or("") };
let ext_mnem = format!("bd{z}{cond_str}{a}{l}"); let ext_mnem = format!("bd{z}{cond_str}{a}{l}");
let ext_ops = format!("{cr}0x{target:08X}"); let ext_ops = format!("{cr}0x{target:08X}");
with_ext(&base_mnem, base_ops, 8, &ext_mnem, ext_ops, 8) with_ext(&base_mnem, base_ops, 8, &ext_mnem, ext_ops, 8)

4
crates/xenia-cpu/tests/golden/extended_mnemonics.json
View File

@@ -366,7 +366,7 @@
"addr": "0x82000000", "addr": "0x82000000",
"mnemonic": "bc", "mnemonic": "bc",
"operands": "16, lt, 0x82000040", "operands": "16, lt, 0x82000040",
"ext_mnemonic": "bdnzge", "ext_mnemonic": "bdnz",
"ext_operands": "0x82000040", "ext_operands": "0x82000040",
"branch_target": "0x82000040" "branch_target": "0x82000040"
}, },
@@ -376,7 +376,7 @@
"addr": "0x82000000", "addr": "0x82000000",
"mnemonic": "bc", "mnemonic": "bc",
"operands": "18, lt, 0x82000040", "operands": "18, lt, 0x82000040",
"ext_mnemonic": "bdzge", "ext_mnemonic": "bdz",
"ext_operands": "0x82000040", "ext_operands": "0x82000040",
"branch_target": "0x82000040" "branch_target": "0x82000040"
}, },