[PR114810][LRA]: Recognize alternatives with lack of available registers for insn and demote them.

  PR114810 was fixed in machine-dependent way.  This patch is a fix of
the PR on LRA side.  LRA chose alternative with constraints `&r,r,ro`
on i686 when all operands of DImode and there are only 6 available
general regs.  The patch recognizes such case and significantly
increase the alternative cost.  It does not reject alternative
completely.  So the fix is safe but it might not work for all
potentially possible cases of registers lack as register classes can
have any relations including subsets and intersections.

gcc/ChangeLog:

	PR target/114810
	* lra-constraints.cc (process_alt_operands): Calculate union reg
	class for the alternative, peak matched regs and required reload
	regs.  Recognize alternatives with lack of available registers and
	make them costly.  Add debug print about this case.

1 files changed, 41 insertions, 2 deletions

diff --git a/gcc/lra-constraints.cc b/gcc/lra-constraints.cc
index 10e3d4e..5b78fd0 100644
--- a/gcc/lra-constraints.cc
+++ b/gcc/lra-constraints.cc
@@ -2127,6 +2127,8 @@ process_alt_operands (int only_alternative)
   /* Numbers of operands which are early clobber registers.  */
   int early_clobbered_nops[MAX_RECOG_OPERANDS];
   enum reg_class curr_alt[MAX_RECOG_OPERANDS];
+  enum reg_class all_this_alternative;
+  int all_used_nregs, all_reload_nregs;
   HARD_REG_SET curr_alt_set[MAX_RECOG_OPERANDS];
   HARD_REG_SET curr_alt_exclude_start_hard_regs[MAX_RECOG_OPERANDS];
   bool curr_alt_match_win[MAX_RECOG_OPERANDS];
@@ -2229,7 +2231,8 @@ process_alt_operands (int only_alternative)
       curr_alt_out_sp_reload_p = false;
       curr_reuse_alt_p = true;
       curr_alt_class_change_p = false;
-      
+      all_this_alternative = NO_REGS;
+      all_used_nregs = all_reload_nregs = 0;
       for (nop = 0; nop < n_operands; nop++)
 	{
 	  const char *p;
@@ -2660,6 +2663,15 @@ process_alt_operands (int only_alternative)
 	  /* Record which operands fit this alternative.  */
 	  if (win)
 	    {
+	      if (early_clobber_p
+		  || curr_static_id->operand[nop].type != OP_OUT)
+		{
+		  all_used_nregs
+		    += ira_reg_class_min_nregs[this_alternative][mode];
+		  all_this_alternative
+		    = (reg_class_subunion
+		       [all_this_alternative][this_alternative]);
+		}
 	      this_alternative_win = true;
 	      if (class_change_p)
 		{
@@ -2781,7 +2793,19 @@ process_alt_operands (int only_alternative)
 		       & ~((ira_prohibited_class_mode_regs
 			    [this_alternative][mode])
 			   | lra_no_alloc_regs));
-		  if (hard_reg_set_empty_p (available_regs))
+		  if (!hard_reg_set_empty_p (available_regs))
+		    {
+		      if (early_clobber_p
+			  || curr_static_id->operand[nop].type != OP_OUT)
+			{
+			  all_reload_nregs
+			    += ira_reg_class_min_nregs[this_alternative][mode];
+			  all_this_alternative
+			    = (reg_class_subunion
+			       [all_this_alternative][this_alternative]);
+			}
+		    }
+		  else
 		    {
 		      /* There are no hard regs holding a value of given
 			 mode.  */
@@ -3217,6 +3241,21 @@ process_alt_operands (int only_alternative)
 		     "            Cycle danger: overall += LRA_MAX_REJECT\n");
 	  overall += LRA_MAX_REJECT;
 	}
+      if (all_this_alternative != NO_REGS
+	  && all_used_nregs != 0 && all_reload_nregs != 0
+	  && (all_used_nregs + all_reload_nregs + 1
+	      >= ira_class_hard_regs_num[all_this_alternative]))
+	{
+	  if (lra_dump_file != NULL)
+	    fprintf
+	      (lra_dump_file,
+	       "            Register starvation: overall += LRA_MAX_REJECT"
+	       "(class=%s,avail=%d,used=%d,reload=%d)\n",
+	       reg_class_names[all_this_alternative],
+	       ira_class_hard_regs_num[all_this_alternative],
+	       all_used_nregs, all_reload_nregs);
+	  overall += LRA_MAX_REJECT;
+	}
       ok_p = true;
       curr_alt_dont_inherit_ops_num = 0;
       for (nop = 0; nop < early_clobbered_regs_num; nop++)