Don't double-count early-clobber matches.

Given a pattern with a number of operands:

(match_operand 0 "" "=&v")
(match_operand 1 "" " v0")
(match_operand 2 "" " v0")
(match_operand 3 "" " v0")

GCC will currently increment "reject" once, for operand 0, and then decrement
it once for each of the other operands, ending with reject == -2 and an
assertion failure.  If there's a conflict then it might try to decrement reject
yet again.

Incidentally, what these patterns are trying to achieve is an allocation in
which operand 0 may match one of the other operands, but may not partially
overlap any of them.  Ideally there'd be a better way to do this.

In any case, it will affect any pattern in which multiple operands may (or
must) match an early-clobber operand.

The patch only allows a reject-- when one has not already occurred, for that
operand.

2018-10-22  Andrew Stubbs  <ams@codesourcery.com>

	gcc/
	* lra-constraints.c (process_alt_operands): New local array,
	matching_early_clobber.  Check matching_early_clobber before
	decrementing reject, and set matching_early_clobber after.

diff --git a/gcc/lra-constraints.c b/gcc/lra-constraints.c
index 774d1ff..3b355a8 100644
--- a/gcc/lra-constraints.c
+++ b/gcc/lra-constraints.c
@@ -1969,6 +1969,7 @@ process_alt_operands (int only_alternative)
       if (!TEST_BIT (preferred, nalt))
 	continue;
 
+      bool matching_early_clobber[MAX_RECOG_OPERANDS];
       curr_small_class_check++;
       overall = losers = addr_losers = 0;
       static_reject = reject = reload_nregs = reload_sum = 0;
@@ -1980,6 +1981,7 @@ process_alt_operands (int only_alternative)
 	    fprintf (lra_dump_file,
 		     "            Staticly defined alt reject+=%d\n", inc);
 	  static_reject += inc;
+	  matching_early_clobber[nop] = 0;
 	}
       reject += static_reject;
       early_clobbered_regs_num = 0;
@@ -2175,7 +2177,11 @@ process_alt_operands (int only_alternative)
 				 "            %d Matching earlyclobber alt:"
 				 " reject--\n",
 				 nop);
-			    reject--;
+			    if (!matching_early_clobber[m])
+			      {
+				reject--;
+				matching_early_clobber[m] = 1;
+			      }
 			  }
 			/* Otherwise we prefer no matching
 			   alternatives because it gives more freedom
@@ -2921,15 +2927,11 @@ process_alt_operands (int only_alternative)
 	      curr_alt_dont_inherit_ops[curr_alt_dont_inherit_ops_num++]
 		= last_conflict_j;
 	      losers++;
-	      /* Early clobber was already reflected in REJECT. */
-	      lra_assert (reject > 0);
 	      if (lra_dump_file != NULL)
 		fprintf
 		  (lra_dump_file,
 		   "            %d Conflict early clobber reload: reject--\n",
 		   i);
-	      reject--;
-	      overall += LRA_LOSER_COST_FACTOR - 1;
 	    }
 	  else
 	    {
@@ -2953,17 +2955,21 @@ process_alt_operands (int only_alternative)
 		}
 	      curr_alt_win[i] = curr_alt_match_win[i] = false;
 	      losers++;
-	      /* Early clobber was already reflected in REJECT. */
-	      lra_assert (reject > 0);
 	      if (lra_dump_file != NULL)
 		fprintf
 		  (lra_dump_file,
 		   "            %d Matched conflict early clobber reloads: "
 		   "reject--\n",
 		   i);
+	    }
+	  /* Early clobber was already reflected in REJECT. */
+	  if (!matching_early_clobber[i])
+	    {
+	      lra_assert (reject > 0);
 	      reject--;
-	      overall += LRA_LOSER_COST_FACTOR - 1;
+	      matching_early_clobber[i] = 1;
 	    }
+	  overall += LRA_LOSER_COST_FACTOR - 1;
 	}
       if (lra_dump_file != NULL)
 	fprintf (lra_dump_file, "          alt=%d,overall=%d,losers=%d,rld_nregs=%d\n",