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[store-merging] Use store order as tie-breaker in sort_by_bitpos

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As Alexander pointed out in the thread starting at [1] the sort_by_bitpos sorting function
was behaving badly when we had multiple stores at the same position.  He fixed that (thanks!)
but we can do better by not returning zero when the bitpositions are equal but by falling back
to comparing the order the stores appear in, which is guaranteed to be unique (barring other
bugs elsewhere).

This patch does that.

Bootstrapped and tested on aarch64-none-linux-gnu.

[1] https://gcc.gnu.org/ml/gcc-patches/2017-07/msg00895.html 

	* gimple-ssa-store-merging.c (sort_by_bitpos): Compare store order
	when bitposition is the same.

From-SVN: r252084
This commit is contained in:
Kyrylo Tkachov 2017-09-13 13:49:50 +00:00 • committed by Kyrylo Tkachov
parent 7dbe3736d5
commit 0f0027d163
2 changed files with 8 additions and 1 deletions
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5
gcc/ChangeLog
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@ -1,3 +1,8 @@
2017-09-13 Kyrylo Tkachov <kyrylo.tkachov@arm.com>
* gimple-ssa-store-merging.c (sort_by_bitpos): Compare store order
when bitposition is the same.
2017-09-13 Richard Biener <rguenther@suse.de>
* dwarf2out.c (output_die_symbol): Remove.

4
gcc/gimple-ssa-store-merging.c
View file

@ -521,7 +521,9 @@ sort_by_bitpos (const void *x, const void *y)
else if ((*tmp)->bitpos > (*tmp2)->bitpos)
return 1;
else
return 0;
/* If they are the same let's use the order which is guaranteed to
be different. */
return (*tmp)->order - (*tmp2)->order;
}
/* Sorting function for store_immediate_info objects.