Re: [GCC 11 backport] Disable generating load/store vector pairs for block copies.

[Michael Meissner <meissner@linux.ibm.com>]

Back port patch (changing .cc to .c) from trunk to GCC 11 committed.

| From 3118d0856b030fe491a170354fed2df570df199f Mon Sep 17 00:00:00 2001
| From: Michael Meissner <meissner@linux.ibm.com>
| Date: Thu, 14 Jul 2022 14:03:37 -0400
| Subject: [PATCH] [BACKPORT] Disable generating load/store vector pairs for block copies.

Testing has found that using load and store vector pair for block copies
can result in a slow down on power10.  This patch disables using the
vector pair instructions for block copies if we are tuning for power10.

2022-06-11   Michael Meissner  <meissner@linux.ibm.com>

gcc/

	* config/rs6000/rs6000.c (rs6000_option_override_internal): Do
	not generate block copies with vector pair instructions if we are
	tuning for power10.  Back port from master branch.
---
 gcc/config/rs6000/rs6000.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/gcc/config/rs6000/rs6000.c b/gcc/config/rs6000/rs6000.c
index 8c89b45922f..73f90f134f8 100644
--- a/gcc/config/rs6000/rs6000.c
+++ b/gcc/config/rs6000/rs6000.c
@@ -4149,7 +4149,10 @@ rs6000_option_override_internal (bool global_init_p)
 
   if (!(rs6000_isa_flags_explicit & OPTION_MASK_BLOCK_OPS_VECTOR_PAIR))
     {
-      if (TARGET_MMA && TARGET_EFFICIENT_UNALIGNED_VSX)
+      /* Do not generate lxvp and stxvp on power10 since there are some
+	 performance issues.  */
+      if (TARGET_MMA && TARGET_EFFICIENT_UNALIGNED_VSX
+	  && rs6000_tune != PROCESSOR_POWER10)
 	rs6000_isa_flags |= OPTION_MASK_BLOCK_OPS_VECTOR_PAIR;
       else
 	rs6000_isa_flags &= ~OPTION_MASK_BLOCK_OPS_VECTOR_PAIR;
-- 
2.35.3


-- 
Michael Meissner, IBM
PO Box 98, Ayer, Massachusetts, USA, 01432
email: meissner@linux.ibm.com