[PATCH 3/3] Use absolute switch table addresses for zero cycle moves.

[Michael Meissner via Gcc-patches]

se absolute switch table addresses for zero cycle moves.

This option enables using absolute addresses in switch tables if the
power10 zero cycle move tuning is turned on.  The combination of using
absolute addresses in switch tables along with zero cycle moves seems to
give the best performance.

I have built and run bootstrapped compilers on little endian power9 and power10
systems.  There were no regressions.  Can I install this patch?

2021-11-19  Michael Meissner  <meiss...@the-meissners.org>

        * config/rs6000/rs6000.c (rs6000_option_override_internal): Use
        absolute addresses in switch tables if power10 zero cycle move
        fusion is enabled.
---
 gcc/config/rs6000/rs6000.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/gcc/config/rs6000/rs6000.c b/gcc/config/rs6000/rs6000.c
index 8531cef0337..dc942765828 100644
--- a/gcc/config/rs6000/rs6000.c
+++ b/gcc/config/rs6000/rs6000.c
@@ -4502,6 +4502,12 @@ rs6000_option_override_internal (bool global_init_p)
       && (rs6000_isa_flags_explicit & OPTION_MASK_P10_FUSION_ZERO_CYCLE) == 0)
     rs6000_isa_flags |= OPTION_MASK_P10_FUSION_ZERO_CYCLE;
 
+  /* If we enable zero cycle move fusion, also switch to absolute addresses in
+     switch tables.  */
+  if (TARGET_P10_FUSION && TARGET_P10_FUSION_ZERO_CYCLE
+      && !global_options_set.x_rs6000_relative_jumptables)
+    rs6000_relative_jumptables = 0;
+
   /* Turn off vector pair/mma options on non-power10 systems.  */
   else if (!TARGET_POWER10 && TARGET_MMA)
     {
-- 
2.31.1


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