[PATCH 07/12] mode-switching: Allow targets to set the mode for EH handlers

[Richard Sandiford <richard.sandiford@arm.com>]

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 759331a2c96..1a825c5004e 100644
--- a/gcc/doc/tm.texi
+++ b/gcc/doc/tm.texi
@@ -10455,6 +10455,12 @@ 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 a7b7aa289d8..5360c1bb2d8 100644
--- a/gcc/doc/tm.texi.in
+++ b/gcc/doc/tm.texi.in
@@ -6979,6 +6979,8 @@ 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 1145350ca26..b8a887d81f7 100644
--- a/gcc/mode-switching.cc
+++ b/gcc/mode-switching.cc
@@ -597,7 +597,10 @@ 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 3dae33522f1..a70275b8abd 100644
--- a/gcc/target.def
+++ b/gcc/target.def
@@ -7070,6 +7070,13 @@ 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\
-- 
2.25.1