From 9505464aec8f95125293c64e2eea9577e9be4700 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 039/157] [Backport][SME] mode-switching: Allow targets to set
 the mode for EH handlers

Reference: https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=4b803fbf839439b1deca660e32d5ced211111dfa

The mode-switching pass already had hooks to say what mode
an entity is in on entry to a function and what mode it must
be in on return.  For SME, we also want to say what mode an
entity is guaranteed to be in on entry to an exception handler.

gcc/
	* target.def (mode_switching.eh_handler): New hook.
	* doc/tm.texi.in (TARGET_MODE_EH_HANDLER): New @hook.
	* doc/tm.texi: Regenerate.
	* mode-switching.cc (optimize_mode_switching): Use eh_handler
	to get the mode on entry to an exception handler.
---
 gcc/doc/tm.texi       | 6 ++++++
 gcc/doc/tm.texi.in    | 2 ++
 gcc/mode-switching.cc | 5 ++++-
 gcc/target.def        | 7 +++++++
 4 files changed, 19 insertions(+), 1 deletion(-)

diff --git a/gcc/doc/tm.texi b/gcc/doc/tm.texi
index 553aa4cf2..4788b3f7a 100644
--- a/gcc/doc/tm.texi
+++ b/gcc/doc/tm.texi
@@ -10321,6 +10321,12 @@ If @code{TARGET_MODE_EXIT} is defined then @code{TARGET_MODE_ENTRY}
 must be defined.
 @end deftypefn
 
+@deftypefn {Target Hook} int TARGET_MODE_EH_HANDLER (int @var{entity})
+If this hook is defined, it should return the mode that @var{entity} is
+guaranteed to be in on entry to an exception handler, or the number of modes
+if there is no such guarantee.
+@end deftypefn
+
 @deftypefn {Target Hook} int TARGET_MODE_PRIORITY (int @var{entity}, int @var{n})
 This hook specifies the order in which modes for @var{entity}
 are processed. 0 is the highest priority,
diff --git a/gcc/doc/tm.texi.in b/gcc/doc/tm.texi.in
index 9ec11b15c..ad343504f 100644
--- a/gcc/doc/tm.texi.in
+++ b/gcc/doc/tm.texi.in
@@ -6926,6 +6926,8 @@ mode or ``no mode'', depending on context.
 
 @hook TARGET_MODE_EXIT
 
+@hook TARGET_MODE_EH_HANDLER
+
 @hook TARGET_MODE_PRIORITY
 
 @node Target Attributes
diff --git a/gcc/mode-switching.cc b/gcc/mode-switching.cc
index 4761c2ff0..9a6ba6cca 100644
--- a/gcc/mode-switching.cc
+++ b/gcc/mode-switching.cc
@@ -596,7 +596,10 @@ optimize_mode_switching (void)
 		gcc_assert (NOTE_INSN_BASIC_BLOCK_P (ins_pos));
 		if (ins_pos != BB_END (bb))
 		  ins_pos = NEXT_INSN (ins_pos);
-		ptr = new_seginfo (no_mode, no_mode, ins_pos, live_now);
+		if (bb_has_eh_pred (bb)
+		    && targetm.mode_switching.eh_handler)
+		  last_mode = targetm.mode_switching.eh_handler (e);
+		ptr = new_seginfo (no_mode, last_mode, ins_pos, live_now);
 		add_seginfo (&tail_ptr, ptr);
 		bitmap_clear_bit (transp_all, bb->index);
 	      }
diff --git a/gcc/target.def b/gcc/target.def
index b87b0f927..bbb482de6 100644
--- a/gcc/target.def
+++ b/gcc/target.def
@@ -7042,6 +7042,13 @@ If @code{TARGET_MODE_EXIT} is defined then @code{TARGET_MODE_ENTRY}\n\
 must be defined.",
  int, (int entity), NULL)
 
+DEFHOOK
+(eh_handler,
+ "If this hook is defined, it should return the mode that @var{entity} is\n\
+guaranteed to be in on entry to an exception handler, or the number of modes\n\
+if there is no such guarantee.",
+ int, (int entity), NULL)
+
 DEFHOOK
 (priority,
  "This hook specifies the order in which modes for @var{entity}\n\
-- 
2.33.0