combine: Print insns we try to combine

This adds some extra debug info to the dump file for combine: print
the insns that are input to try_combine.  I was worried printing more
will make the dump file only harder to read, but especially the info
from the REG_DEAD notes is invaluable.


	* combine (try_combine): Print the insns input to try_combine to the
	dump file.

From-SVN: r254365

gcc/ChangeLog

+2017-11-02  Segher Boessenkool  <segher@kernel.crashing.org>
+
+	* combine (try_combine): Print the insns input to try_combine to the
+	dump file.
+
 2017-11-02  Steve Ellcey  <sellcey@cavium.com>
 
 	PR target/79868

gcc/combine.c

@@ -2771,6 +2771,13 @@ try_combine (rtx_insn *i3, rtx_insn *i2, rtx_insn *i1, rtx_insn *i0,
       else
 	fprintf (dump_file, "\nTrying %d -> %d:\n",
 		 INSN_UID (i2), INSN_UID (i3));
+
+      if (i0)
+	dump_insn_slim (dump_file, i0);
+      if (i1)
+	dump_insn_slim (dump_file, i1);
+      dump_insn_slim (dump_file, i2);
+      dump_insn_slim (dump_file, i3);
     }
 
   /* If multiple insns feed into one of I2 or I3, they can be in any