| commit | 192d13ea4df1e9535e8736175231798bcde42bb5 | [log] [tgz] |
|---|---|---|
| author | Luke Lau <luke@igalia.com> | Tue Sep 09 09:30:33 2025 +0800 |
| committer | GitHub <noreply@github.com> | Tue Sep 09 01:30:33 2025 +0000 |
| tree | 8453c2705abecf233402d544b52aca2319e83dcc | |
| parent | 71f98a13b32b85ff6fe1c7b047d8b70c5e7bcc7d [diff] |
[RISCV] Undo fneg (fmul x, y) -> fmul x, (fneg y) transform (#157388)
InstCombine will hoist an fneg through an fmul, but not for fadd/fsub.
This prevents us from matching fmsub and fnmadd in some cases.
This patch adds a DAG combine to undo this in InstCombine, which helps
some hot loops in 508.namd_r:
@@ -983,18 +983,15 @@
fld ft2, 48(a5)
fld ft3, 64(a5)
fld ft4, 72(a5)
- fneg.d fa0, fa0
- fneg.d ft0, ft0
- fneg.d ft2, ft2
fmul.d fa3, ft5, fa3
fmul.d fa0, fa3, fa0
fmul.d ft0, fa3, ft0
fmul.d fa3, fa3, ft2
fld ft2, 0(s1)
fmul.d fa4, ft5, fa4
- fmadd.d fa2, fa4, fa2, fa0
- fmadd.d ft6, fa4, ft6, ft0
- fmadd.d fa4, fa4, ft1, fa3
+ fmsub.d fa2, fa4, fa2, fa0
+ fmsub.d ft6, fa4, ft6, ft0
+ fmsub.d fa4, fa4, ft1, fa3
This gives a [1.77% improvement in both instruction count and runtime on
508.namd_r](https://lnt.lukelau.me/db_default/v4/nts/profile/1/1022/1021)
This also causes some more fnegs to be sunk after a bitcast to integer,
so they're now done as xor. From glancing at some of the schedules for
WriteFSGN my guess is that this is also profitable.
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