[PATCH] reload_cse_move2add: Handle trivial single_set:s

[Hans-Peter Nilsson <hp@axis.com>]

Tested cris-elf, bootstrapped & checked native
x86_64-pc-linux-gnu for good measure.  Ok to commit?

If it wasn't for there already being an auto_inc_dec pass,
this looks like a good place to put it, considering the
framework data.  (BTW, current auto-inc-dec generation is so
poor that you can replace half of what auto_inc_dec does
with a few peephole2s.)

brgds, H-P

-- >8 --
The reload_cse_move2add part of "postreload" handled only
insns whose PATTERN was a SET.  That excludes insns that
e.g. clobber a flags register, which it does only for
"simplicity".  The patch extends the "simplicity" to most
single_set insns.  For a subset of those insns there's still
an assumption; that the single_set of a PARALLEL insn is the
first element in the PARALLEL.  If the assumption fails,
it's no biggie; the optimization just isn't performed.
Don't let the name deceive you, this optimization doesn't
hit often, but as often (or as rarely) for LRA as for reload
at least on e.g. cris-elf where the biggest effect was seen
in reducing repeated addresses in copies from fixed-address
arrays, like in gcc.c-torture/compile/pr78694.c.

	* postreload.cc (move2add_use_add2_insn): Handle
	trivial single_sets.  Rename variable PAT to SET.
	(move2add_use_add3_insn, reload_cse_move2add): Similar.
---
 gcc/postreload.cc | 67 +++++++++++++++++++++++++++--------------------
 1 file changed, 38 insertions(+), 29 deletions(-)

diff --git a/gcc/postreload.cc b/gcc/postreload.cc
index fb392651e1b6..996206f589d3 100644
--- a/gcc/postreload.cc
+++ b/gcc/postreload.cc
@@ -1744,8 +1744,8 @@ static bool
 move2add_use_add2_insn (scalar_int_mode mode, rtx reg, rtx sym, rtx off,
 			rtx_insn *insn)
 {
-  rtx pat = PATTERN (insn);
-  rtx src = SET_SRC (pat);
+  rtx set = single_set (insn);
+  rtx src = SET_SRC (set);
   int regno = REGNO (reg);
   rtx new_src = gen_int_mode (UINTVAL (off) - reg_offset[regno], mode);
   bool speed = optimize_bb_for_speed_p (BLOCK_FOR_INSN (insn));
@@ -1764,21 +1764,21 @@ move2add_use_add2_insn (scalar_int_mode mode, rtx reg, rtx sym, rtx off,
 	 (reg)), would be discarded.  Maybe we should
 	 try a truncMN pattern?  */
       if (INTVAL (off) == reg_offset [regno])
-	changed = validate_change (insn, &SET_SRC (pat), reg, 0);
+	changed = validate_change (insn, &SET_SRC (set), reg, 0);
     }
   else
     {
       struct full_rtx_costs oldcst, newcst;
       rtx tem = gen_rtx_PLUS (mode, reg, new_src);
 
-      get_full_set_rtx_cost (pat, &oldcst);
-      SET_SRC (pat) = tem;
-      get_full_set_rtx_cost (pat, &newcst);
-      SET_SRC (pat) = src;
+      get_full_set_rtx_cost (set, &oldcst);
+      SET_SRC (set) = tem;
+      get_full_set_rtx_cost (set, &newcst);
+      SET_SRC (set) = src;
 
       if (costs_lt_p (&newcst, &oldcst, speed)
 	  && have_add2_insn (reg, new_src))
-	changed = validate_change (insn, &SET_SRC (pat), tem, 0);	
+	changed = validate_change (insn, &SET_SRC (set), tem, 0);
       else if (sym == NULL_RTX && mode != BImode)
 	{
 	  scalar_int_mode narrow_mode;
@@ -1796,10 +1796,15 @@ move2add_use_add2_insn (scalar_int_mode mode, rtx reg, rtx sym, rtx off,
 							    narrow_reg),
 				   narrow_src);
 		  get_full_set_rtx_cost (new_set, &newcst);
-		  if (costs_lt_p (&newcst, &oldcst, speed))
+
+		  /* We perform this replacement only if NEXT is either a
+		     naked SET, or else its single_set is the first element
+		     in a PARALLEL.  */
+		  rtx *setloc = GET_CODE (PATTERN (insn)) == PARALLEL
+		    ? &XEXP (PATTERN (insn), 0) : &PATTERN (insn);
+		  if (*setloc == set && costs_lt_p (&newcst, &oldcst, speed))
 		    {
-		      changed = validate_change (insn, &PATTERN (insn),
-						 new_set, 0);
+		      changed = validate_change (insn, setloc, new_set, 0);
 		      if (changed)
 			break;
 		    }
@@ -1825,8 +1830,8 @@ static bool
 move2add_use_add3_insn (scalar_int_mode mode, rtx reg, rtx sym, rtx off,
 			rtx_insn *insn)
 {
-  rtx pat = PATTERN (insn);
-  rtx src = SET_SRC (pat);
+  rtx set = single_set (insn);
+  rtx src = SET_SRC (set);
   int regno = REGNO (reg);
   int min_regno = 0;
   bool speed = optimize_bb_for_speed_p (BLOCK_FOR_INSN (insn));
@@ -1836,10 +1841,10 @@ move2add_use_add3_insn (scalar_int_mode mode, rtx reg, rtx sym, rtx off,
   rtx plus_expr;
 
   init_costs_to_max (&mincst);
-  get_full_set_rtx_cost (pat, &oldcst);
+  get_full_set_rtx_cost (set, &oldcst);
 
   plus_expr = gen_rtx_PLUS (GET_MODE (reg), reg, const0_rtx);
-  SET_SRC (pat) = plus_expr;
+  SET_SRC (set) = plus_expr;
 
   for (i = 0; i < FIRST_PSEUDO_REGISTER; i++)
     if (move2add_valid_value_p (i, mode)
@@ -1864,7 +1869,7 @@ move2add_use_add3_insn (scalar_int_mode mode, rtx reg, rtx sym, rtx off,
 	else
 	  {
 	    XEXP (plus_expr, 1) = new_src;
-	    get_full_set_rtx_cost (pat, &newcst);
+	    get_full_set_rtx_cost (set, &newcst);
 
 	    if (costs_lt_p (&newcst, &mincst, speed))
 	      {
@@ -1873,7 +1878,7 @@ move2add_use_add3_insn (scalar_int_mode mode, rtx reg, rtx sym, rtx off,
 	      }
 	  }
       }
-  SET_SRC (pat) = src;
+  SET_SRC (set) = src;
 
   if (costs_lt_p (&mincst, &oldcst, speed))
     {
@@ -1886,7 +1891,7 @@ move2add_use_add3_insn (scalar_int_mode mode, rtx reg, rtx sym, rtx off,
 				      GET_MODE (reg));
 	  tem = gen_rtx_PLUS (GET_MODE (reg), tem, new_src);
 	}
-      if (validate_change (insn, &SET_SRC (pat), tem, 0))
+      if (validate_change (insn, &SET_SRC (set), tem, 0))
 	changed = true;
     }
   reg_set_luid[regno] = move2add_luid;
@@ -1916,7 +1921,7 @@ reload_cse_move2add (rtx_insn *first)
   move2add_luid = 2;
   for (insn = first; insn; insn = NEXT_INSN (insn), move2add_luid++)
     {
-      rtx pat, note;
+      rtx set, note;
 
       if (LABEL_P (insn))
 	{
@@ -1929,17 +1934,17 @@ reload_cse_move2add (rtx_insn *first)
 	}
       if (! INSN_P (insn))
 	continue;
-      pat = PATTERN (insn);
+      set = single_set (insn);
       /* For simplicity, we only perform this optimization on
-	 straightforward SETs.  */
+	 single-sets.  */
       scalar_int_mode mode;
-      if (GET_CODE (pat) == SET
-	  && REG_P (SET_DEST (pat))
-	  && is_a <scalar_int_mode> (GET_MODE (SET_DEST (pat)), &mode))
+      if (set
+	  && REG_P (SET_DEST (set))
+	  && is_a <scalar_int_mode> (GET_MODE (SET_DEST (set)), &mode))
 	{
-	  rtx reg = SET_DEST (pat);
+	  rtx reg = SET_DEST (set);
 	  int regno = REGNO (reg);
-	  rtx src = SET_SRC (pat);
+	  rtx src = SET_SRC (set);
 
 	  /* Check if we have valid information on the contents of this
 	     register in the mode of REG.  */
@@ -2021,13 +2028,15 @@ reload_cse_move2add (rtx_insn *first)
 			  SET_SRC (set) = old_src;
 			  costs_add_n_insns (&oldcst, 1);
 
-			  if (costs_lt_p (&newcst, &oldcst, speed)
+			  rtx *setloc = GET_CODE (PATTERN (next)) == PARALLEL
+			    ? &XEXP (PATTERN (next), 0) : &PATTERN (next);
+			  if (*setloc == set
+			      && costs_lt_p (&newcst, &oldcst, speed)
 			      && have_add2_insn (reg, new_src))
 			    {
 			      rtx newpat = gen_rtx_SET (reg, tem);
 			      success
-				= validate_change (next, &PATTERN (next),
-						   newpat, 0);
+				= validate_change (next, setloc, newpat, 0);
 			    }
 			}
 		      if (success)
-- 
2.30.2