Zen4 tuning part 2

Zen4 tuning part 2

Adds tunes needed for zen4 microarchitecture.  I added two new knobs.
TARGET_AVX512_SPLIT_REGS which is used to specify that internally 512 vectors
are split to 256 vectors.  This affects vectorization costs and reassociation
width. It probably should also affect RTX costs however I doubt it is very useful
since RTL optimizers are usually not judging between 256 and 512 vectors.

I also added X86_TUNE_AVOID_256FMA_CHAINS. Since fma has improved in zen4 this
flag may not be a win except for very specific benchmarks. I am still doing some
more detailed testing here.

Oherwise I disabled gathers on zen4 for 2 parts nad 4 parts. We can open code them
and since the latencies has only increased since zen3 opencoding is better than
actual instrucction.  This shows at 4 tsvc benchmarks.

I ended up setting AVX256_OPTIMAL. This is a compromise.  There are some tsvc
benchmarks that increase noticeably (up to 250%) however there are also few
regressions.  Most of these can be solved by incrasing vec_perm cost in the
vectorizer.  However this does not cure about 14% regression on x264 that is
quite important.  Here we produce vectorized loops for avx512 that probably
would be faster if the loops in question had high enough iteration count.
We hit this problem with avx256 too: since the loop iterates few times, only
prologues/epilogues are used.  Adding another round of prologue/epilogue
code does not make it better.

Finally I enabled avx stores for constnat sized memcpy and memset.  I am not
sure why this is an opt-in feature.  I think for most hardware this is a win.

gcc/ChangeLog:

2022-12-22  Jan Hubicka  <hubicka@ucw.cz>

	* config/i386/i386-expand.cc (ix86_expand_set_or_cpymem): Add
	TARGET_AVX512_SPLIT_REGS
	* config/i386/i386-options.cc (ix86_option_override_internal):
	Honor x86_TONE_AVOID_256FMA_CHAINS.
	* config/i386/i386.cc (ix86_vec_cost): Honor TARGET_AVX512_SPLIT_REGS.
	(ix86_reassociation_width): Likewise.
	* config/i386/i386.h (TARGET_AVX512_SPLIT_REGS): New tune.
	* config/i386/x86-tune.def (X86_TUNE_USE_GATHER_2PARTS): Disable
	for znver4.
	(X86_TUNE_USE_GATHER_4PARTS): Likewise.
	(X86_TUNE_AVOID_256FMA_CHAINS): Set for znver4.
	(X86_TUNE_AVOID_512FMA_CHAINS): New utne; set for znver4.
	(X86_TUNE_AVX256_OPTIMAL): Add znver4.
	(X86_TUNE_AVX512_SPLIT_REGS): New tune.
	(X86_TUNE_AVX256_MOVE_BY_PIECES): Add znver1-3.
	(X86_TUNE_AVX256_STORE_BY_PIECES): Add znver1-3.
	(X86_TUNE_AVX512_MOVE_BY_PIECES): Add znver4.
	(X86_TUNE_AVX512_STORE_BY_PIECES): Add znver4.

(cherry picked from commit eef81eefcdc2a58111e50eb2162ea1f5becc8004)