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Re: [PATCH] Avoid optimizing memory references with side effects in compare-elim.c
> On Jun 6, 2018, at 11:53 AM, Eric Botcazou <ebotcazou@adacore.com> wrote:
>
>> That simplifies the patch, which now looks like this. Ok for trunk?
>>
>> paul
>>
>> gcc/ChangeLog:
>>
>> 2018-06-05 Paul Koning <ni1d@arrl.net>
>>
>> * compare-elim.c (try_merge_compare): Don't merge compare if
>> address contains a side effect.
>> * gcc.c-torture/compile/20180605-1.c: New test case.
>
> The patch is OK, but its ChangeLog is not. :-) It does not modify one
> function but two (try_merge_compare and try_eliminate_compare). I would
> suggest using "diff -up" to generate patches with more context.
Yes, sorry. I normally use the subversion internal diff which doesn't do this.
Here is a corrected version. Ok with this change?
paul
gcc/ChangeLog:
2018-06-06 Paul Koning <ni1d@arrl.net>
* compare-elim.c (try_merge_compare): Don't merge compare if
address contains a side effect.
(try_eliminate_compare): Likewise.
* gcc.c-torture/compile/20180605-1.c: New test case.
Index: compare-elim.c
===================================================================
--- compare-elim.c (revision 261207)
+++ compare-elim.c (working copy)
@@ -690,6 +690,13 @@ try_merge_compare (struct comparison *cm
return false;
rtx src = SET_SRC (set);
+
+ /* If the source uses addressing modes with side effects, we can't
+ do the merge because we'd end up with a PARALLEL that has two
+ instances of that side effect in it. */
+ if (side_effects_p (src))
+ return false;
+
rtx flags = maybe_select_cc_mode (cmp, src, CONST0_RTX (GET_MODE (src)));
if (!flags)
{
@@ -809,6 +816,12 @@ try_eliminate_compare (struct comparison
else
return false;
+ /* If the source uses addressing modes with side effects, we can't
+ do the merge because we'd end up with a PARALLEL that has two
+ instances of that side effect in it. */
+ if (side_effects_p (cmp_src))
+ return false;
+
/* Determine if we ought to use a different CC_MODE here. */
flags = maybe_select_cc_mode (cmp, cmp_src, in_b);
if (flags == NULL)
Index: testsuite/gcc.c-torture/compile/20180605-1.c
===================================================================
--- testsuite/gcc.c-torture/compile/20180605-1.c (nonexistent)
+++ testsuite/gcc.c-torture/compile/20180605-1.c (working copy)
@@ -0,0 +1,9 @@
+void f (int *p, int n)
+{
+ int j = 0, k;
+
+ for (int i = 0; i < n; i++)
+ if ((k = *p++) > 0)
+ j += k;
+ return j;
+}