[APX CCMP] Adjust startegy for selecting ccmp candidates

For general ccmp scenario, the tree sequence is like

_1 = (a < b)
_2 = (c < d)
_3 = _1 & _2

current ccmp expanding will try to swap compare order for _1 and _2,
compare the expansion cost/cost2 for expanding _1 or _2 first, then
return the sequence with lower cost.

It is possible that one expansion succeeds and the other fails.
For example, x86 has int ccmp but not fp ccmp, so a combined fp and
int comparison must be ordered such that the fp comparison happens
first.  The costs are not meaningful for failed expansions.

Check the expand_ccmp_next result ret and ret2, returns the valid one
before cost comparison.

gcc/ChangeLog:

	* ccmp.cc (expand_ccmp_expr_1): Check ret and ret2 of
	expand_ccmp_next, returns the valid one first instead of
	comparing cost.

1 files changed, 9 insertions, 1 deletions

diff --git a/gcc/ccmp.cc b/gcc/ccmp.cc
index 7cb525a..4d50708 100644
--- a/gcc/ccmp.cc
+++ b/gcc/ccmp.cc
@@ -247,7 +247,15 @@ expand_ccmp_expr_1 (gimple *g, rtx_insn **prep_seq, rtx_insn **gen_seq)
 	      cost2 = seq_cost (prep_seq_2, speed_p);
 	      cost2 += seq_cost (gen_seq_2, speed_p);
 	    }
-	  if (cost2 < cost1)
+
+	  /* It's possible that one expansion succeeds and the other
+	     fails.
+	     For example, x86 has int ccmp but not fp ccmp, and so a
+	     combined fp and int comparison must be ordered such that
+	     the fp comparison happens first. The costs are not
+	     meaningful for failed expansions.  */
+
+	  if (ret2 && (!ret || cost2 < cost1))
 	    {
 	      *prep_seq = prep_seq_2;
 	      *gen_seq = gen_seq_2;