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Fix optimization bug.

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GCC-PR rtl-optimization/34628
	* combine.c (try_combine): Stop and undo after the first combination
	if an autoincrement side-effect on the first insn has effectively
	been lost.

The issue was detected in OpenBSD but their fix was not very good. Huge
thanks to the upstream author, Eric Botcazou, for permitting the use of
this patch under GPLv2.

MFC after:	5 days
This commit is contained in:
pfg 2014-01-06 00:52:39 +00:00
parent 0d91dd56df
commit 9f411e6c04
1 changed files with 11 additions and 6 deletions
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17
contrib/gcc/combine.c
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@ -2370,12 +2370,17 @@ try_combine (rtx i3, rtx i2, rtx i1, int *new_direct_jump_p)
if (i1 && GET_CODE (newpat) != CLOBBER)
{
/* Before we can do this substitution, we must redo the test done
above (see detailed comments there) that ensures that I1DEST
isn't mentioned in any SETs in NEWPAT that are field assignments. */
if (! combinable_i3pat (NULL_RTX, &newpat, i1dest, NULL_RTX,
0, (rtx*) 0))
/* Check that an autoincrement side-effect on I1 has not been lost.
This happens if I1DEST is mentioned in I2 and dies there, and
has disappeared from the new pattern. */
if ((FIND_REG_INC_NOTE (i1, NULL_RTX) != 0
&& !i1_feeds_i3
&& dead_or_set_p (i2, i1dest)
&& !reg_overlap_mentioned_p (i1dest, newpat))
/* Before we can do this substitution, we must redo the test done
above (see detailed comments there) that ensures that I1DEST
isn't mentioned in any SETs in NEWPAT that are field assignments. */
|| !combinable_i3pat (NULL_RTX, &newpat, i1dest, NULL_RTX, 0, 0))
{
undo_all ();
return 0;