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From c0aaf329d9c547b249ac120a8d1995d8546a1edb Mon Sep 17 00:00:00 2001
From: Richard Sandiford <richard.sandiford@arm.com>
Date: Sat, 11 Nov 2023 17:28:57 +0000
Subject: [PATCH 038/157] [Backport][SME] mode-switching: Tweak entry/exit
handling
Reference: https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=e59ec35276599805cdc6c3979d8a167b027d286e
An entity isn't transparent in a block that requires a specific mode.
optimize_mode_switching took that into account for normal insns,
but didn't for the exit block. Later patches misbehaved because
of this.
In contrast, an entity was correctly marked as non-transparent
in the entry block, but the reasoning seemed a bit convoluted.
It also referred to a function that no longer exists.
Since KILL = ~TRANSP, the entity is by definition not transparent
in a block that defines the entity, so I think we can make it so
without comment.
Finally, the exit handling was nested in the entry handling,
but that doesn't seem necessary. A target could say that an
entity is undefined on entry but must be defined on return,
on a "be liberal in what you accept, be conservative in what
you do" principle.
gcc/
* mode-switching.cc (optimize_mode_switching): Mark the exit
block as nontransparent if it requires a specific mode.
Handle the entry and exit mode as sibling rather than nested
concepts. Remove outdated comment.
---
gcc/mode-switching.cc | 34 +++++++++++++++-------------------
1 file changed, 15 insertions(+), 19 deletions(-)
diff --git a/gcc/mode-switching.cc b/gcc/mode-switching.cc
index 4d2b9e284..4761c2ff0 100644
--- a/gcc/mode-switching.cc
+++ b/gcc/mode-switching.cc
@@ -649,34 +649,30 @@ optimize_mode_switching (void)
}
if (targetm.mode_switching.entry && targetm.mode_switching.exit)
{
- int mode = targetm.mode_switching.entry (e);
-
info[post_entry->index].mode_out =
info[post_entry->index].mode_in = no_mode;
- if (pre_exit)
- {
- info[pre_exit->index].mode_out =
- info[pre_exit->index].mode_in = no_mode;
- }
+ int mode = targetm.mode_switching.entry (e);
if (mode != no_mode)
{
- bb = post_entry;
-
- /* By always making this nontransparent, we save
- an extra check in make_preds_opaque. We also
- need this to avoid confusing pre_edge_lcm when
- antic is cleared but transp and comp are set. */
- bitmap_clear_bit (transp_all, bb->index);
-
/* Insert a fake computing definition of MODE into entry
blocks which compute no mode. This represents the mode on
entry. */
- info[bb->index].computing = mode;
+ info[post_entry->index].computing = mode;
+ bitmap_clear_bit (transp_all, post_entry->index);
+ }
- if (pre_exit)
- info[pre_exit->index].seginfo->mode =
- targetm.mode_switching.exit (e);
+ if (pre_exit)
+ {
+ info[pre_exit->index].mode_out =
+ info[pre_exit->index].mode_in = no_mode;
+
+ int mode = targetm.mode_switching.exit (e);
+ if (mode != no_mode)
+ {
+ info[pre_exit->index].seginfo->mode = mode;
+ bitmap_clear_bit (transp_all, pre_exit->index);
+ }
}
}
--
2.33.0
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