[gcc(refs/vendors/ARM/heads/morello)] morello: Account for a zero MOVE_RATIO when estimating the cost of a move

[gcc(refs/vendors/ARM/heads/morello)] morello: Account for a zero MOVE_RATIO when estimating the cost of a move

[Matthew Malcomson]

https://gcc.gnu.org/g:41494f7e04b40df3d6d25ff5811557ed8e692880

commit 41494f7e04b40df3d6d25ff5811557ed8e692880
Author: Stam Markianos-Wright <stam.markianos-wright@arm.com>
Date:   Thu Nov 4 15:40:13 2021 +0000

    morello: Account for a zero MOVE_RATIO when estimating the cost of a move
    
    In disabling the move-by-pieces infrastructure we set MOVE_RATIO
    to zero in the AArch64 backend.
    This source location, however, used the MOVE_RATIO to guess if
    a move would later result in a memcpy call and so this would always
    be TRUE, resulting in the assumption that a memcpy would always happen
    and the move cost being set to 4.
    This patch adds a !MOVE_RATIO condition to stop this invalid behaviour
    and always fall through to the estimating based on the MOVE_MAX_PIECES
    calculation.
    
    This also led to a detection of an upstream bug in the Graphite pass,
    so that pass has now been disabled to avoid this wrong code. This is:
    https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103247

Diff:
---
 gcc/graphite.c    |  8 ++++++++
 gcc/tree-inline.c | 10 ++++++++--
 2 files changed, 16 insertions(+), 2 deletions(-)

diff --git a/gcc/graphite.c b/gcc/graphite.c
index 1c702d09500..a6627b0b778 100644
--- a/gcc/graphite.c
+++ b/gcc/graphite.c
@@ -462,6 +462,14 @@ graphite_transform_loops (void)
     if (dbg_cnt (graphite_scop))
       {
 	scop->isl_context = ctx;
+
+	/* MORELLO TODO (OPTIMISED): Disabling this optimisation pass after
+	   detecting an optimisation that had an impact on correctness for
+	   Morello and for base AArch64. Details at:
+	   https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103247 .  */
+	if (targetm.capability_mode().exists())
+	  continue;
+
 	if (!build_poly_scop (scop))
 	  continue;
 
diff --git a/gcc/tree-inline.c b/gcc/tree-inline.c
index 3160ca3f88a..48cdb8da59c 100644
--- a/gcc/tree-inline.c
+++ b/gcc/tree-inline.c
@@ -4129,8 +4129,14 @@ estimate_move_cost (tree type, bool ARG_UNUSED (speed_p))
     }
 
   size = int_size_in_bytes (type);
-
-  if (size < 0 || size > MOVE_MAX_PIECES * MOVE_RATIO (speed_p))
+  /* For capability targets MOVE_RATIO is set to zero to disable the
+     move-by-pieces infrastructure and avoid invalidating capabilities, so
+     also take that into account and use a slightly different reasonable
+     calculation to see if the move will result in a memcpy call.  */
+  if (size < 0 || size > (MOVE_RATIO (speed_p) ? MOVE_RATIO (speed_p)
+					       : MOVE_MAX_PIECES
+						 / (speed_p ? 2 : 4))
+			  * MOVE_MAX_PIECES)
     /* Cost of a memcpy call, 3 arguments and the call.  */
     return 4;
   else