Wilco pointed out that when the Dot Product instructions are available we can use them
to generate an even more efficient expansion for the [us]sadv16qi optab.
Instead of the current:
uabdl2 v0.8h, v1.16b, v2.16b
uabal v0.8h, v1.8b, v2.8b
uadalp v3.4s, v0.8h
we can generate:
(1) mov v4.16b, 1
(2) uabd v0.16b, v1.16b, v2.16b
(3) udot v3.4s, v0.16b, v4.16b
Instruction (1) can be CSEd across multiple such expansions and even hoisted outside of loops,
so when this sequence appears frequently back-to-back (like in x264_r) we essentially only have 2 instructions
per sum. Also, the UDOT instruction does the byte-to-word accumulation in one step, which allows us to use
the much simpler UABD instruction before it.
This makes it a shorter and lower-latency sequence overall for targets that support it.
* config/aarch64/iterators.md (MAX_OPP): New code attr.
* config/aarch64/aarch64-simd.md (*aarch64_<su>abd<mode>_3): Rename to...
(aarch64_<su>abd<mode>_3): ... This.
(<sur>sadv16qi): Add TARGET_DOTPROD expansion.
* gcc.target/aarch64/ssadv16qi.c: Add +nodotprod to pragma.
* gcc.target/aarch64/usadv16qi.c: Likewise.
* gcc.target/aarch64/ssadv16qi-dotprod.c: New test.
* gcc.target/aarch64/usadv16qi-dotprod.c: Likewise.
From-SVN: r271863
