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combine: Correct comments about combine_validate_cost

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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.
This commit is contained in:
Hans-Peter Nilsson 2025-04-15 06:08:36 +02:00 • committed by Hans-Peter Nilsson
parent ac31e41c58
commit a4f81e168e
1 changed files with 3 additions and 3 deletions
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6
gcc/combine.cc
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@ -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)
/* 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 ();