[gcc r14-10718] Zen5 tuning part 2: disable gather and scatter

[Jan Hubicka]

https://gcc.gnu.org/g:3d0a91130eceaf428387ba314cfdfceb99b51709

commit r14-10718-g3d0a91130eceaf428387ba314cfdfceb99b51709
Author: Jan Hubicka <jh@suse.cz>
Date:   Tue Sep 3 15:07:41 2024 +0200

    Zen5 tuning part 2: disable gather and scatter
    
    We disable gathers for zen4.  It seems that gather has improved a bit compared
    to zen4 and Zen5 optimization manual suggests "Avoid GATHER instructions when
    the indices are known ahead of time. Vector loads followed by shuffles result
    in a higher load bandwidth." however the situation seems to be more
    complicated.
    
    gather is 5-10% loss on parest benchmark as well as 30% loss on sparse dot
    products in TSVC. Curiously enough breaking these out into microbenchmark
    reversed the situation and it turns out that the performance depends on
    how indices are distributed.  gather is loss if indices are sequential,
    neutral if they are random and win for some strides (4, 8).
    
    This seems to be similar to earlier zens, so I think (especially for
    backporting znver5 support) that it makes sense to be conistent and disable
    gather unless we work out a good heuristics on when to use it. Since we
    typically do not know the indices in advance, I don't see how that can be done.
    
    I opened PR116582 with some examples of wins and loses
    
    gcc/ChangeLog:
    
            * config/i386/x86-tune.def (X86_TUNE_USE_GATHER_2PARTS): Disable for
            ZNVER5.
            (X86_TUNE_USE_SCATTER_2PARTS): Disable for ZNVER5.
            (X86_TUNE_USE_GATHER_4PARTS): Disable for ZNVER5.
            (X86_TUNE_USE_SCATTER_4PARTS): Disable for ZNVER5.
            (X86_TUNE_USE_GATHER_8PARTS): Disable for ZNVER5.
            (X86_TUNE_USE_SCATTER_8PARTS): Disable for ZNVER5.
    
    (cherry picked from commit d82edbe92eed53a479736fcbbe6d54d0fb42daa4)

Diff:
---
 gcc/config/i386/x86-tune.def | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/gcc/config/i386/x86-tune.def b/gcc/config/i386/x86-tune.def
index 4a3bd15d0ad2..01324a88a3be 100644
--- a/gcc/config/i386/x86-tune.def
+++ b/gcc/config/i386/x86-tune.def
@@ -483,35 +483,35 @@ DEF_TUNE (X86_TUNE_AVOID_4BYTE_PREFIXES, "avoid_4byte_prefixes",
 /* X86_TUNE_USE_GATHER_2PARTS: Use gather instructions for vectors with 2
    elements.  */
 DEF_TUNE (X86_TUNE_USE_GATHER_2PARTS, "use_gather_2parts",
-	  ~(m_ZNVER1 | m_ZNVER2 | m_ZNVER3 | m_ZNVER4 | m_CORE_HYBRID
+	  ~(m_ZNVER | m_CORE_HYBRID
 	    | m_YONGFENG | m_CORE_ATOM | m_GENERIC | m_GDS))
 
 /* X86_TUNE_USE_SCATTER_2PARTS: Use scater instructions for vectors with 2
    elements.  */
 DEF_TUNE (X86_TUNE_USE_SCATTER_2PARTS, "use_scatter_2parts",
-	  ~(m_ZNVER4))
+	  ~(m_ZNVER4 | m_ZNVER5))
 
 /* X86_TUNE_USE_GATHER_4PARTS: Use gather instructions for vectors with 4
    elements.  */
 DEF_TUNE (X86_TUNE_USE_GATHER_4PARTS, "use_gather_4parts",
-	  ~(m_ZNVER1 | m_ZNVER2 | m_ZNVER3 | m_ZNVER4 | m_CORE_HYBRID
+	  ~(m_ZNVER | m_CORE_HYBRID
 	    | m_YONGFENG | m_CORE_ATOM | m_GENERIC | m_GDS))
 
 /* X86_TUNE_USE_SCATTER_4PARTS: Use scater instructions for vectors with 4
    elements.  */
 DEF_TUNE (X86_TUNE_USE_SCATTER_4PARTS, "use_scatter_4parts",
-	  ~(m_ZNVER4))
+	  ~(m_ZNVER4 | m_ZNVER5))
 
 /* X86_TUNE_USE_GATHER: Use gather instructions for vectors with 8 or more
    elements.  */
 DEF_TUNE (X86_TUNE_USE_GATHER_8PARTS, "use_gather_8parts",
-	  ~(m_ZNVER1 | m_ZNVER2 | m_ZNVER4 | m_CORE_HYBRID | m_CORE_ATOM
+	  ~(m_ZNVER1 | m_ZNVER2 | m_ZNVER4 | m_ZNVER5 | m_CORE_HYBRID | m_CORE_ATOM
 	    | m_YONGFENG | m_GENERIC | m_GDS))
 
 /* X86_TUNE_USE_SCATTER: Use scater instructions for vectors with 8 or more
    elements.  */
 DEF_TUNE (X86_TUNE_USE_SCATTER_8PARTS, "use_scatter_8parts",
-	  ~(m_ZNVER4))
+	  ~(m_ZNVER4 | m_ZNVER5))
 
 /* X86_TUNE_AVOID_128FMA_CHAINS: Avoid creating loops with tight 128bit or
    smaller FMA chain.  */