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doloop.c (doloop_valid_p): Check for LTU and GTU as well. 

2001-11-29  Zoltan Hidvegi  <hzoli@hzoli.2y.net>

        * doloop.c (doloop_valid_p): Check for LTU and GTU as well.

From-SVN: r47468
This commit is contained in:
Zoltan Hidvegi 2001-11-30 02:16:31 +00:00 committed by David Edelsohn
parent 20c29ebe49
commit c7c737361b
2 changed files with 25 additions and 6 deletions
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4
gcc/ChangeLog
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@ -1,3 +1,7 @@
2001-11-29 Zoltan Hidvegi <hzoli@hzoli.2y.net>
* doloop.c (doloop_valid_p): Check for LTU and GTU as well.
2001-11-29 Aldy Hernandez <aldyh@redhat.com>
* config/rs6000/rs6000.c (function_arg): Unnamed vector arguments

27
gcc/doloop.c
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@ -353,23 +353,38 @@ doloop_valid_p (loop, jump_insn)
&& ((loop_info->comparison_code == LEU
&& INTVAL (loop_info->increment) > 0)
|| (loop_info->comparison_code == GEU
&& INTVAL (loop_info->increment) < 0)))
&& INTVAL (loop_info->increment) < 0)
|| (loop_info->comparison_code == LTU
&& INTVAL (loop_info->increment) > 1)
|| (loop_info->comparison_code == GTU
&& INTVAL (loop_info->increment) < -1)))
{
/* If the comparison is LEU and the comparison value is UINT_MAX
then the loop will not terminate. Similarly, if the
comparison code is GEU and the initial value is 0, the loop
will not terminate.
Note that with LE and GE, the loop behaviour can be
implementation dependent if an overflow occurs, say between
INT_MAX and INT_MAX + 1. We thus don't have to worry about
these two cases.
If the absolute increment is not 1, the loop can be infinite
even with LTU/GTU, e.g. for (i = 3; i > 0; i -= 2)
Note that with LE and GE, the loop behaviour is undefined
(C++ standard section 5 clause 5) if an overflow occurs, say
between INT_MAX and INT_MAX + 1. We thus don't have to worry
about these two cases.
??? We could compute these conditions at run-time and have a
additional jump around the loop to ensure an infinite loop.
However, it is very unlikely that this is the intended
behaviour of the loop and checking for these rare boundary
conditions would pessimize all other code. */
conditions would pessimize all other code.
If the loop is executed only a few times an extra check to
restart the loop could use up most of the benefits of using a
count register loop. Note however, that normally, this
restart branch would never execute, so it could be predicted
well by the CPU. We should generate the pessimistic code by
default, and have an option, e.g. -funsafe-loops that would
enable count-register loops in this case. */
if (loop_dump_stream)
fprintf (loop_dump_stream,
"Doloop: Possible infinite iteration case ignored.\n");