mode-switching: Pass set of live registers to the needed hook

The emit hook already takes the set of live hard registers as input.
This patch passes it to the needed hook too.  SME uses this to
optimise the mode choice based on whether state is live or dead.

The main caller already had access to the required info, but the
special handling of return values did not.

gcc/
	* target.def (mode_switching.needed): Add a regs_live parameter.
	* doc/tm.texi: Regenerate.
	* config/epiphany/epiphany-protos.h (epiphany_mode_needed): Update
	accordingly.
	* config/epiphany/epiphany.cc (epiphany_mode_needed): Likewise.
	* config/epiphany/mode-switch-use.cc (insert_uses): Likewise.
	* config/i386/i386.cc (ix86_mode_needed): Likewise.
	* config/riscv/riscv.cc (riscv_mode_needed): Likewise.
	* config/sh/sh.cc (sh_mode_needed): Likewise.
	* mode-switching.cc (optimize_mode_switching): Likewise.
	(create_pre_exit): Likewise, using the DF simulate functions
	to calculate the required information.

9 files changed, 27 insertions, 13 deletions

diff --git a/gcc/config/epiphany/epiphany-protos.h b/gcc/config/epiphany/epiphany-protos.h
index 72c141c..ef49a1e 100644
--- a/gcc/config/epiphany/epiphany-protos.h
+++ b/gcc/config/epiphany/epiphany-protos.h
@@ -44,7 +44,9 @@ extern void emit_set_fp_mode (int entity, int mode, int prev_mode,
 #endif
 extern void epiphany_insert_mode_switch_use (rtx_insn *insn, int, int);
 extern void epiphany_expand_set_fp_mode (rtx *operands);
-extern int epiphany_mode_needed (int entity, rtx_insn *insn);
+#ifdef HARD_CONST
+extern int epiphany_mode_needed (int entity, rtx_insn *insn, HARD_REG_SET);
+#endif
 extern int epiphany_mode_after (int entity, int last_mode, rtx_insn *insn);
 extern bool epiphany_epilogue_uses (int regno);
 extern bool epiphany_optimize_mode_switching (int entity);
diff --git a/gcc/config/epiphany/epiphany.cc b/gcc/config/epiphany/epiphany.cc
index a5460db..60a9b49 100644
--- a/gcc/config/epiphany/epiphany.cc
+++ b/gcc/config/epiphany/epiphany.cc
@@ -2400,7 +2400,7 @@ epiphany_mode_priority (int entity, int priority)
 }
 
 int
-epiphany_mode_needed (int entity, rtx_insn *insn)
+epiphany_mode_needed (int entity, rtx_insn *insn, HARD_REG_SET)
 {
   enum attr_fp_mode mode;
 
diff --git a/gcc/config/epiphany/mode-switch-use.cc b/gcc/config/epiphany/mode-switch-use.cc
index 7153061..183b9b7 100644
--- a/gcc/config/epiphany/mode-switch-use.cc
+++ b/gcc/config/epiphany/mode-switch-use.cc
@@ -58,7 +58,7 @@ insert_uses (void)
 	{
 	  if (!INSN_P (insn))
 	    continue;
-	  mode = epiphany_mode_needed (e, insn);
+	  mode = epiphany_mode_needed (e, insn, {});
 	  if (mode == no_mode)
 	    continue;
 	  if (target_insert_mode_switch_use)
diff --git a/gcc/config/i386/i386.cc b/gcc/config/i386/i386.cc
index eec9b42..a041e87 100644
--- a/gcc/config/i386/i386.cc
+++ b/gcc/config/i386/i386.cc
@@ -15060,7 +15060,7 @@ ix86_i387_mode_needed (int entity, rtx_insn *insn)
    prior to the execution of insn.  */
 
 static int
-ix86_mode_needed (int entity, rtx_insn *insn)
+ix86_mode_needed (int entity, rtx_insn *insn, HARD_REG_SET)
 {
   switch (entity)
     {
diff --git a/gcc/config/riscv/riscv.cc b/gcc/config/riscv/riscv.cc
index fa2d4d4..750eaf9 100644
--- a/gcc/config/riscv/riscv.cc
+++ b/gcc/config/riscv/riscv.cc
@@ -9426,7 +9426,7 @@ riscv_frm_mode_needed (rtx_insn *cur_insn, int code)
    prior to the execution of insn.  */
 
 static int
-riscv_mode_needed (int entity, rtx_insn *insn)
+riscv_mode_needed (int entity, rtx_insn *insn, HARD_REG_SET)
 {
   int code = recog_memoized (insn);
 
diff --git a/gcc/config/sh/sh.cc b/gcc/config/sh/sh.cc
index 294faf7..c363490 100644
--- a/gcc/config/sh/sh.cc
+++ b/gcc/config/sh/sh.cc
@@ -195,7 +195,7 @@ static int calc_live_regs (HARD_REG_SET *);
 static HOST_WIDE_INT rounded_frame_size (int);
 static bool sh_frame_pointer_required (void);
 static void sh_emit_mode_set (int, int, int, HARD_REG_SET);
-static int sh_mode_needed (int, rtx_insn *);
+static int sh_mode_needed (int, rtx_insn *, HARD_REG_SET);
 static int sh_mode_after (int, int, rtx_insn *);
 static int sh_mode_entry (int);
 static int sh_mode_exit (int);
@@ -12531,7 +12531,7 @@ sh_emit_mode_set (int entity ATTRIBUTE_UNUSED, int mode,
 }
 
 static int
-sh_mode_needed (int entity ATTRIBUTE_UNUSED, rtx_insn *insn)
+sh_mode_needed (int entity ATTRIBUTE_UNUSED, rtx_insn *insn, HARD_REG_SET)
 {
   return recog_memoized (insn) >= 0  ? get_attr_fp_mode (insn) : FP_MODE_NONE;
 }
diff --git a/gcc/doc/tm.texi b/gcc/doc/tm.texi
index 1a825c5..144b3f8 100644
--- a/gcc/doc/tm.texi
+++ b/gcc/doc/tm.texi
@@ -10414,12 +10414,13 @@ known.  Sets of a lower numbered entity will be emitted before
 sets of a higher numbered entity to a mode of the same or lower priority.
 @end deftypefn
 
-@deftypefn {Target Hook} int TARGET_MODE_NEEDED (int @var{entity}, rtx_insn *@var{insn})
+@deftypefn {Target Hook} int TARGET_MODE_NEEDED (int @var{entity}, rtx_insn *@var{insn}, HARD_REG_SET @var{regs_live})
 @var{entity} is an integer specifying a mode-switched entity.
 If @code{OPTIMIZE_MODE_SWITCHING} is defined, you must define this hook
 to return the mode that @var{entity} must be switched into prior to the
 execution of @var{insn}, or the number of modes if @var{insn} has no
-such requirement.
+such requirement.  @var{regs_live} contains the set of hard registers
+that are live before @var{insn}.
 @end deftypefn
 
 @deftypefn {Target Hook} int TARGET_MODE_AFTER (int @var{entity}, int @var{mode}, rtx_insn *@var{insn})
diff --git a/gcc/mode-switching.cc b/gcc/mode-switching.cc
index b8a887d..c5fe90b 100644
--- a/gcc/mode-switching.cc
+++ b/gcc/mode-switching.cc
@@ -254,6 +254,9 @@ create_pre_exit (int n_entities, int *entity_map, const int *num_modes)
 	    && GET_CODE (PATTERN (last_insn)) == USE
 	    && GET_CODE ((ret_reg = XEXP (PATTERN (last_insn), 0))) == REG)
 	  {
+	    auto_bitmap live;
+	    df_simulate_initialize_backwards (src_bb, live);
+
 	    int ret_start = REGNO (ret_reg);
 	    int nregs = REG_NREGS (ret_reg);
 	    int ret_end = ret_start + nregs;
@@ -262,6 +265,8 @@ create_pre_exit (int n_entities, int *entity_map, const int *num_modes)
 	    bool forced_late_switch = false;
 	    rtx_insn *before_return_copy;
 
+	    df_simulate_one_insn_backwards (src_bb, last_insn, live);
+
 	    do
 	      {
 		rtx_insn *return_copy = PREV_INSN (last_insn);
@@ -269,6 +274,8 @@ create_pre_exit (int n_entities, int *entity_map, const int *num_modes)
 		int copy_start, copy_num;
 		int j;
 
+		df_simulate_one_insn_backwards (src_bb, return_copy, live);
+
 		if (NONDEBUG_INSN_P (return_copy))
 		  {
 		    /* When using SJLJ exceptions, the call to the
@@ -368,11 +375,14 @@ create_pre_exit (int n_entities, int *entity_map, const int *num_modes)
 		       the case for floating point on SH4 - then it might
 		       be set by an arithmetic operation that needs a
 		       different mode than the exit block.  */
+		    HARD_REG_SET hard_regs_live;
+		    REG_SET_TO_HARD_REG_SET (hard_regs_live, live);
 		    for (j = n_entities - 1; j >= 0; j--)
 		      {
 			int e = entity_map[j];
 			int mode =
-			  targetm.mode_switching.needed (e, return_copy);
+			  targetm.mode_switching.needed (e, return_copy,
+							 hard_regs_live);
 
 			if (mode != num_modes[e]
 			    && mode != targetm.mode_switching.exit (e))
@@ -610,7 +620,7 @@ optimize_mode_switching (void)
 	    {
 	      if (INSN_P (insn))
 		{
-		  int mode = targetm.mode_switching.needed (e, insn);
+		  int mode = targetm.mode_switching.needed (e, insn, live_now);
 		  rtx link;
 
 		  if (mode != no_mode && mode != last_mode)
diff --git a/gcc/target.def b/gcc/target.def
index a70275b..50bad18 100644
--- a/gcc/target.def
+++ b/gcc/target.def
@@ -7031,8 +7031,9 @@ DEFHOOK
 If @code{OPTIMIZE_MODE_SWITCHING} is defined, you must define this hook\n\
 to return the mode that @var{entity} must be switched into prior to the\n\
 execution of @var{insn}, or the number of modes if @var{insn} has no\n\
-such requirement.",
- int, (int entity, rtx_insn *insn), NULL)
+such requirement.  @var{regs_live} contains the set of hard registers\n\
+that are live before @var{insn}.",
+ int, (int entity, rtx_insn *insn, HARD_REG_SET regs_live), NULL)
 
 DEFHOOK
 (after,