On Mon, 20 May 2019, Richard Biener wrote:
On Sun, May 19, 2019 at 6:16 PM Marc Glisse <marc.gli...@inria.fr> wrote:
Hello,
2 pieces:
- the first one handles the case where the denominator is negative. It
doesn't happen often with exact_div, so I don't handle it everywhere, but
this one looked trivial
- handle the case where a pointer difference is cast to an unsigned type
before being compared to a constant (I hit this in std::vector). With some
range info we could probably handle some non-constant cases as well...
The second piece breaks Walloca-13.c (-Walloca-larger-than=100 -O2)
void f (void*);
void g (int *p, int *q)
{
__SIZE_TYPE__ n = (__SIZE_TYPE__)(p - q);
if (n < 100)
f (__builtin_alloca (n));
}
At the time of walloca2, we have
_1 = p_5(D) - q_6(D);
# RANGE [-2305843009213693952, 2305843009213693951]
_2 = _1 /[ex] 4;
# RANGE ~[2305843009213693952, 16140901064495857663]
n_7 = (long unsigned intD.10) _2;
_11 = (long unsigned intD.10) _1;
if (_11 <= 396)
[...]
_3 = allocaD.1059 (n_7);
and warn.
That's indeed to complicated relation of _11 to n_7 for
VRP predicate discovery.
However, DOM3 later produces
_1 = p_5(D) - q_6(D);
_11 = (long unsigned intD.10) _1;
if (_11 <= 396)
while _11 vs. _1 works fine.
[...]
# RANGE [0, 99] NONZERO 127
_2 = _1 /[ex] 4;
# RANGE [0, 99] NONZERO 127
n_7 = (long unsigned intD.10) _2;
_3 = allocaD.1059 (n_7);
so I am tempted to say that the walloca2 pass is too early, xfail the
testcase and file an issue...
Hmm, there's a DOM pass before walloca2 already and moving
walloca2 after loop opts doesn't look like the best thing to do?
I suppose it's not DOM but sinking that does the important transform
here? That is,
Index: gcc/passes.def
===================================================================
--- gcc/passes.def (revision 271395)
+++ gcc/passes.def (working copy)
@@ -241,9 +241,9 @@ along with GCC; see the file COPYING3.
NEXT_PASS (pass_optimize_bswap);
NEXT_PASS (pass_laddress);
NEXT_PASS (pass_lim);
- NEXT_PASS (pass_walloca, false);
NEXT_PASS (pass_pre);
NEXT_PASS (pass_sink_code);
+ NEXT_PASS (pass_walloca, false);
NEXT_PASS (pass_sancov);
NEXT_PASS (pass_asan);
NEXT_PASS (pass_tsan);
fixes it?
I will check, but I don't think walloca uses any kind of on-demand VRP, so
we still need some pass to update the ranges after sinking, which doesn't
seem to happen until the next DOM pass.
--
Marc Glisse
