[gcc r13-5725] Enable 512 bit vector for zen4

[gcc r13-5725] Enable 512 bit vector for zen4

[Jan Hubicka]

https://gcc.gnu.org/g:a7502c4a614238ac3f80271886b217b156bdf923

commit r13-5725-ga7502c4a614238ac3f80271886b217b156bdf923
Author: Jan Hubicka <jh@suse.cz>
Date:   Tue Feb 7 05:23:00 2023 +0100

    Enable 512 bit vector for zen4
    
    While internally 512 registers are splits into two 256 halves, 512 bit vectors
    reduces number of instructions to retire and has chance to improve paralelism.
    There are few tsvc benchmarks that improves significantly:
    
               runtime
    benchmark  256bit  512bit
    s2275      48.57   20.67    -58%
    s311       32.29   16.06    -50%
    s312       32.30   16.07    -50%
    vsumr      32.30   16.07    -50%
    s314       10.77   5.42     -50%
    s313       21.52   10.85    -50%
    vdotr      43.05   21.69    -50%
    s316       10.80   5.64     -48%
    s235       61.72   33.91    -45%
    s161       15.91   9.95     -38%
    s3251      32.13   20.31    -36%
    
    And there are no benchmarks with off-noise regression.  The basic matrix
    multiplication loop improves by 32%.  It is also expected that 512 bit
    vectors are more power effecient (I can't masure that).
    
    The down side is that loops with low trip counts may get slower when the
    unvectorized prologue and epilogue is hit more often.  With SPECfp this
    problem happens with x264 (12% regression) and bwaves (6% regression)
    and this is tracked in
    https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108410
    and will need more work on vectorizer to support masked epilogues.
    
    After some additional testing it seems that using 512 bit vectors by
    default is now overall better choice.
    
    Bootstrapped/regtested x86_64-linux. Plan to commit it tomorrow.
    
            * config/i386/x86-tune.def (X86_TUNE_AVX256_OPTIMAL): Turn off
            for znver4.

Diff:
---
 gcc/config/i386/x86-tune.def | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/gcc/config/i386/x86-tune.def b/gcc/config/i386/x86-tune.def
index c78dad07c88..3054656a12c 100644
--- a/gcc/config/i386/x86-tune.def
+++ b/gcc/config/i386/x86-tune.def
@@ -551,7 +551,7 @@ DEF_TUNE (X86_TUNE_AVX128_OPTIMAL, "avx128_optimal", m_BDVER | m_BTVER2
 
 /* X86_TUNE_AVX256_OPTIMAL: Use 256-bit AVX instructions instead of 512-bit AVX
    instructions in the auto-vectorizer.  */
-DEF_TUNE (X86_TUNE_AVX256_OPTIMAL, "avx256_optimal", m_CORE_AVX512 | m_ZNVER4)
+DEF_TUNE (X86_TUNE_AVX256_OPTIMAL, "avx256_optimal", m_CORE_AVX512)
 
 /* X86_TUNE_AVX256_SPLIT_REGS: if true, AVX512 ops are split into two AVX256 ops.  */
 DEF_TUNE (X86_TUNE_AVX512_SPLIT_REGS, "avx512_split_regs", m_ZNVER4)