combine: Correct comments about combine_validate_cost

Fix misleading comments.  That function only determines whether
replacements cost more; it doesn't actually *validate* costs as being
cheaper.

For example, it returns true also if it for various reasons cannot
determine the costs, or if the new cost is the same, like when doing
an identity replacement.  The code has been the same since
r0-59417-g64b8935d4809f3.

	* combine.cc: Correct comments about combine_validate_cost.

diff --git a/gcc/combine.cc b/gcc/combine.cc
index 5f085187cfef6b1db9f85e0c77df07aef413a96c..e1186087dff489fa2679180ec21a9df05a997bfd 100644 (file)
--- a/gcc/combine.cc
+++ b/gcc/combine.cc
@@ -815,7 +815,7 @@ do_SUBST_LINK (struct insn_link **into, struct insn_link *newval)
 #define SUBST_LINK(oldval, newval) do_SUBST_LINK (&oldval, newval)
 \f
 /* Subroutine of try_combine.  Determine whether the replacement patterns
-   NEWPAT, NEWI2PAT and NEWOTHERPAT are cheaper according to insn_cost
+   NEWPAT, NEWI2PAT and NEWOTHERPAT are more expensive according to insn_cost
    than the original sequence I0, I1, I2, I3 and undobuf.other_insn.  Note
    that I0, I1 and/or NEWI2PAT may be NULL_RTX.  Similarly, NEWOTHERPAT and
    undobuf.other_insn may also both be NULL_RTX.  Return false if the cost
@@ -4129,8 +4129,8 @@ try_combine (rtx_insn *i3, rtx_insn *i2, rtx_insn *i1, rtx_insn *i0,
        }
     }
 
-  /* Only allow this combination if insn_cost reports that the
-     replacement instructions are cheaper than the originals.  */
+  /* Reject this combination if insn_cost reports that the replacement
+     instructions are more expensive than the originals.  */
   if (!combine_validate_cost (i0, i1, i2, i3, newpat, newi2pat, other_pat))
     {
       undo_all ();