Hi,
Here's v2 of the patch with Jakub's suggestions incorporated. Bootstrapped
and tested on powerpc64le-linux-gnu with no regressions. Is this ok for
trunk?
Eventually this should be backported to all active releases as well.
Ok for that after a week or so of burn-in? (And after 7.2, I imagine.)
Thanks,
Bill
[gcc]
2017-08-03 Bill Schmidt <wschm...@linux.vnet.ibm.com>
Jakub Jelinek <ja...@redhat.com>
PR tree-optimization/81503
* gimple-ssa-strength-reduction.c (replace_mult_candidate): Ensure
folded constant fits in the target type.
[gcc/testsuite]
2017-08-03 Bill Schmidt <wschm...@linux.vnet.ibm.com>
Jakub Jelinek <ja...@redhat.com>
PR tree-optimization/81503
* gcc.c-torture/execute/pr81503.c: New file.
Index: gcc/gimple-ssa-strength-reduction.c
===================================================================
--- gcc/gimple-ssa-strength-reduction.c (revision 250791)
+++ gcc/gimple-ssa-strength-reduction.c (working copy)
@@ -2074,6 +2074,10 @@ replace_mult_candidate (slsr_cand_t c, tree basis_
{
tree target_type = TREE_TYPE (gimple_assign_lhs (c->cand_stmt));
enum tree_code cand_code = gimple_assign_rhs_code (c->cand_stmt);
+ unsigned int prec = TYPE_PRECISION (target_type);
+ tree maxval = (POINTER_TYPE_P (target_type)
+ ? TYPE_MAX_VALUE (sizetype)
+ : TYPE_MAX_VALUE (target_type));
/* It is highly unlikely, but possible, that the resulting
bump doesn't fit in a HWI. Abandon the replacement
@@ -2082,6 +2086,17 @@ replace_mult_candidate (slsr_cand_t c, tree basis_
types but allows for safe negation without twisted logic. */
if (wi::fits_shwi_p (bump)
&& bump.to_shwi () != HOST_WIDE_INT_MIN
+ /* It is more likely that the bump doesn't fit in the target
+ type, so check whether constraining it to that type changes
+ the value. For a signed type, the value mustn't change.
+ For an unsigned type, the value may only change to a
+ congruent value (for negative bumps). */
+ && (TYPE_UNSIGNED (target_type)
+ ? wi::eq_p (wi::neg_p (bump)
+ ? bump + wi::to_widest (maxval) + 1
+ : bump,
+ wi::zext (bump, prec))
+ : wi::eq_p (bump, wi::sext (bump, prec)))
/* It is not useful to replace casts, copies, negates, or adds of
an SSA name and a constant. */
&& cand_code != SSA_NAME
Index: gcc/testsuite/gcc.c-torture/execute/pr81503.c
===================================================================
--- gcc/testsuite/gcc.c-torture/execute/pr81503.c (nonexistent)
+++ gcc/testsuite/gcc.c-torture/execute/pr81503.c (working copy)
@@ -0,0 +1,15 @@
+unsigned short a = 41461;
+unsigned short b = 3419;
+int c = 0;
+
+void foo() {
+ if (a + b * ~(0 != 5))
+ c = -~(b * ~(0 != 5)) + 2147483647;
+}
+
+int main() {
+ foo();
+ if (c != 2147476810)
+ return -1;
+ return 0;
+}
On 8/3/17 1:02 PM, Bill Schmidt wrote:
>> On Aug 3, 2017, at 11:39 AM, Jakub Jelinek <ja...@redhat.com> wrote:
>>
>> On Thu, Aug 03, 2017 at 11:29:44AM -0500, Bill Schmidt wrote:
>>>> And, wouldn't it be more readable to use:
>>>> && (TYPE_UNSIGNED (target_type)
>>>> ? (wi::eq_p (bump, wi::zext (bump, prec))
>>>> || wi::eq_p (bump + wi::to_widest (maxval) + 1,
>>>> wi::zext (bump, prec)))
>>>> : wi::eq_p (bump, wi::sext (bump, prec)))
>>>> ?
>>> Probably. As noted, it's all becoming a bit unreadable with too
>>> much negative logic in a long conditional, so I want to clean that
>>> up in a follow-up.
>>>
>>>> For TYPE_UNSIGNED, do you actually need any restriction?
>>>> What kind of bump values are wrong for unsigned types and why?
>>> If the value of the bump is actually larger than the precision of the
>>> type (not likely except for quite small types), say 2 * (maxval + 1)
>>> which is congruent to 0, the replacement is wrong.
>> Ah, ok. Anyway, for unsigned type, perhaps it could be written as:
>> && (TYPE_UNSIGNED (target_type)
>> ? wi::eq_p (wi::neg_p (bump) ? bump + wi::to_widest (maxval) + 1
>> : bump, wi::zext (bump, prec))
>> : wi::eq_p (bump, wi::sext (bump, prec)))
>> I mean, if bump >= 0, then the bump + wi::to_widest (maxval) + 1
>> value has no chance to be equal to zero extended bump, and
>> for bump < 0 only that one has a chance.
> Yeah, that's true. And arguably my case for the really large bump
> causing problems is kind of thin, because the program is probably
> already broken in that case anyway. But I think I will sleep better
> having the check in there, as somebody other than SLSR will catch
> the bug then. ;-)
>
> Thanks for all the help with this one. These corner cases are
> always tricky, and I appreciate the extra eyeballs.
>
> Bill
>
>> Jakub
>>
