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loop.c (strength_reduce): Automatically unroll loops if the unrolled loop size is smaller than the rolled... 

* loop.c (strength_reduce): Automatically unroll loops if the
        unrolled loop size is smaller than the rolled loop size.

Co-Authored-By: Jeffrey A Law <law@cygnus.com>

From-SVN: r28841
This commit is contained in:
Michael Tiemann 1999-08-25 06:51:15 +00:00 committed by Jeff Law
parent 3ad4781182
commit 73049ebce3
2 changed files with 37 additions and 3 deletions
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4
gcc/ChangeLog
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@ -4,6 +4,10 @@ Tue Aug 24 23:43:03 1999 Mark Mitchell <mark@codesourcery.com>
NOTE_INSN_EH_REGION_END correctly.
Tue Aug 24 23:26:44 1999 Michael Tiemann <tiemann@holodeck.cygnus.com>
Jeff Law <law@cygnus.com>
* loop.c (strength_reduce): Automatically unroll loops if the
unrolled loop size is smaller than the rolled loop size.
* loop.c (insert_bct): Replace use of sdiv_optab with asr_optab
and delete comment that code should be rewritten.

36
gcc/loop.c
View File

@ -3705,6 +3705,7 @@ strength_reduce (scan_start, end, loop_top, insn_count,
int n_extra_increment;
struct loop_info loop_iteration_info;
struct loop_info *loop_info = &loop_iteration_info;
int unrolled_insn_copies;
/* If scan_start points to the loop exit test, we have to be wary of
subversive use of gotos inside expression statements. */
@ -5133,11 +5134,40 @@ strength_reduce (scan_start, end, loop_top, insn_count,
INSN_CODE (p) = -1;
}
if (loop_info->n_iterations > 0)
{
/* When we completely unroll a loop we will likely not need the increment
of the loop BIV and we will not need the conditional branch at the
end of the loop. */
unrolled_insn_copies = insn_count - 2;
#ifdef HAVE_cc0
/* When we completely unroll a loop on a HAVE_cc0 machine we will not
need the comparison before the conditional branch at the end of the
loop. */
unrolled_insn_copies = insn_count - 2;
#endif
/* We'll need one copy for each loop iteration. */
unrolled_insn_copies *= loop_info->n_iterations;
/* A little slop to account for the ability to remove initialization
code, better CSE, and other secondary benefits of completely
unrolling some loops. */
unrolled_insn_copies -= 1;
/* Clamp the value. */
if (unrolled_insn_copies < 0)
unrolled_insn_copies = 0;
}
/* Unroll loops from within strength reduction so that we can use the
induction variable information that strength_reduce has already
collected. */
if (unroll_p)
collected. Always unroll loops that would be as small or smaller
unrolled than when rolled. */
if (unroll_p
|| (loop_info->n_iterations > 0
&& unrolled_insn_copies <= insn_count))
unroll_loop (loop_end, insn_count, loop_start, end_insert_before,
loop_info, 1);