On Fri, 16 May 2014, Jeff Law wrote:
> On 05/14/14 03:06, Richard Biener wrote:
> >
> > The following fixes pre/post-inc/dec gimplification of promoted
> > integer types. There is the issue with the way TYPE_OVERFLOW_UNDEFINED
> > is related to TYPE_OVERFLOW_WRAPS and the (non-)semantics of
> > -fno-strict-overflow.
> >
> > In this case, with -On -fno-strict-overflow for a variable of
> > type short we have !TYPE_OVERFLOW_WRAPS _and_ !TYPE_OVERFLOW_UNDEFINED
> > (so we're in an "undefined" area). Which means that
> > !TYPE_OVERFLOW_UNDEFINED doesn't imply that overflow wraps.
> >
> > Thus the gimplification has to play on the safe side and
> > always use an unsigned type unless the user specifies -fwrapv
> > (the flag with a proper semantic meaning).
> >
> > That is, it seems to be the case that what predicate to use
> > (TYPE_OVERFLOW_WRAPS or TYPE_OVERFLOW_UNDEFINED, independent
> > on whether you invert it), depends on the use-case in a very
> > awkward (and error-prone) way.
> >
> > Bootstrap and regtest pending on x86_64-unknown-linux-gnu, ok
> > if that succeeds (I expect to have to adjust some testcases)?
> >
> > Thanks,
> > Richard.
> >
> > 2014-05-14 Richard Biener <rguent...@suse.de>
> >
> > c-family/
> > * c-gimplify.c (c_gimplify_expr): Gimplify self-modify expressions
> > using unsigned arithmetic if overflow does not wrap instead of
> > if overflow is undefined.
> >
> > * c-c++-common/torture/pr61184.c: New testcase.
> Seems reasonable to me.
If it is then I'd strongly suggest to make -fno-strict-overflow
imply -fwrapv. Otherwise for -fno-strict-overflow we can
neither rely on signed arithmetic wrapping nor rely on it
invoking undefined behavior - instead it's in lala-land as far
as the middle-end is concerned (and get's us the worst of
both -fwrapv and -fno-wrapv).
Well, it turns out after re-visiting the bug, that the issue
lies in VRP instead as it doesn't detect [0, +INF] -> [0, +INF(OVF)]
as a lattice change and thus it misses visiting dependent
stmts again.
Bootstrap and regtest in progress on x86_64-unknown-linux-gnu.
Thanks,
Richard.
2014-05-19 Richard Biener <rguent...@suse.de>
PR tree-optimization/61184
* tree-vrp.c (is_negative_overflow_infinity): Use
TREE_OVERFLOW_P and do that check first.
(is_positive_overflow_infinity): Likewise.
(is_overflow_infinity): Likewise.
(vrp_operand_equal_p): Properly treat operands with
differing overflow as not equal.
* c-c++-common/torture/pr61184.c: New testcase.
Index: gcc/tree-vrp.c
===================================================================
*** gcc/tree-vrp.c (revision 210607)
--- gcc/tree-vrp.c (working copy)
*************** positive_overflow_infinity (tree type)
*** 293,301 ****
static inline bool
is_negative_overflow_infinity (const_tree val)
{
! return (needs_overflow_infinity (TREE_TYPE (val))
! && CONSTANT_CLASS_P (val)
! && TREE_OVERFLOW (val)
&& vrp_val_is_min (val));
}
--- 293,300 ----
static inline bool
is_negative_overflow_infinity (const_tree val)
{
! return (TREE_OVERFLOW_P (val)
! && needs_overflow_infinity (TREE_TYPE (val))
&& vrp_val_is_min (val));
}
*************** is_negative_overflow_infinity (const_tre
*** 304,312 ****
static inline bool
is_positive_overflow_infinity (const_tree val)
{
! return (needs_overflow_infinity (TREE_TYPE (val))
! && CONSTANT_CLASS_P (val)
! && TREE_OVERFLOW (val)
&& vrp_val_is_max (val));
}
--- 303,310 ----
static inline bool
is_positive_overflow_infinity (const_tree val)
{
! return (TREE_OVERFLOW_P (val)
! && needs_overflow_infinity (TREE_TYPE (val))
&& vrp_val_is_max (val));
}
*************** is_positive_overflow_infinity (const_tre
*** 315,323 ****
static inline bool
is_overflow_infinity (const_tree val)
{
! return (needs_overflow_infinity (TREE_TYPE (val))
! && CONSTANT_CLASS_P (val)
! && TREE_OVERFLOW (val)
&& (vrp_val_is_min (val) || vrp_val_is_max (val)));
}
--- 313,320 ----
static inline bool
is_overflow_infinity (const_tree val)
{
! return (TREE_OVERFLOW_P (val)
! && needs_overflow_infinity (TREE_TYPE (val))
&& (vrp_val_is_min (val) || vrp_val_is_max (val)));
}
*************** vrp_operand_equal_p (const_tree val1, co
*** 791,799 ****
return true;
if (!val1 || !val2 || !operand_equal_p (val1, val2, 0))
return false;
! if (is_overflow_infinity (val1))
! return is_overflow_infinity (val2);
! return true;
}
/* Return true, if the bitmaps B1 and B2 are equal. */
--- 788,794 ----
return true;
if (!val1 || !val2 || !operand_equal_p (val1, val2, 0))
return false;
! return is_overflow_infinity (val1) == is_overflow_infinity (val2);
}
/* Return true, if the bitmaps B1 and B2 are equal. */
Index: gcc/testsuite/c-c++-common/torture/pr61184.c
===================================================================
*** gcc/testsuite/c-c++-common/torture/pr61184.c (revision 0)
--- gcc/testsuite/c-c++-common/torture/pr61184.c (revision 0)
***************
*** 0 ****
--- 1,18 ----
+ /* { dg-do run } */
+ /* { dg-additional-options "-fno-strict-overflow" } */
+
+ short a;
+
+ void
+ foo (void)
+ {
+ for (a = 0; a >= 0; a++)
+ ;
+ }
+
+ int
+ main ()
+ {
+ foo ();
+ return 0;
+ }
