[Bug tree-optimization/94125] [9/10 Regression] wrong code at -O3 on x86_64-linux-gnu
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94125
--- Comment #9 from rguenther at suse dot de ---
On Sun, 15 Mar 2020, amker at gcc dot gnu.org wrote:
> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94125
>
> --- Comment #7 from bin cheng ---
> Patch at https://gcc.gnu.org/pipermail/gcc-patches/2020-March/542038.html
> It's a latent bug exposed by the mentioned alias analysis change, however:
>
>
> unsigned char b, f;
> short d[1][8][1], *g = [0][3][0];
>
> int
> main ()
> {
> int k[] = { 0, 0, 0, 4, 0, 0 };
> for (int c = 2; c >= 0; c--)
> {
> b = f;
> *g = k[c + 3];
> k[c + 1] = 0;
> }
> for (int i = 0; i < 8; i++)
> if (d[0][i][0] != 0)
> __builtin_abort ();
> return 0;
> }
>
> We can't tell no-alias info for pairs and . Is this expected
> or
> should be improved?
This is expected when g is not static [const] (we should discover it
as const) or when not using LTO (which should as well promote the
variable to const short *). Adding a restrict qualifier to g should
also solve it.
[Bug tree-optimization/94125] [9/10 Regression] wrong code at -O3 on x86_64-linux-gnu
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94125 --- Comment #8 from CVS Commits --- The master branch has been updated by Bin Cheng : https://gcc.gnu.org/g:e4e9a59105a81cdd6c1328b0a5ed9fe4cc82840e commit r10-7184-ge4e9a59105a81cdd6c1328b0a5ed9fe4cc82840e Author: Bin Cheng Date: Mon Mar 16 11:09:14 2020 +0800 Update post order number for merged SCC. Function loop_distribution::break_alias_scc_partitions needs to compute SCC with runtime alias edges skipped. As a result, partitions could be re-assigned larger post order number than SCC's precedent partition and distributed before the precedent one. This fixes the issue by updating the merged partition to the minimal post order in SCC. gcc/ PR tree-optimization/94125 * tree-loop-distribution.c (loop_distribution::break_alias_scc_partitions): Update post order number for merged scc. gcc/testsuite/ PR tree-optimization/94125 * gcc.dg/tree-ssa/pr94125.c: New test.
[Bug tree-optimization/94125] [9/10 Regression] wrong code at -O3 on x86_64-linux-gnu
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94125
--- Comment #7 from bin cheng ---
Patch at https://gcc.gnu.org/pipermail/gcc-patches/2020-March/542038.html
It's a latent bug exposed by the mentioned alias analysis change, however:
unsigned char b, f;
short d[1][8][1], *g = [0][3][0];
int
main ()
{
int k[] = { 0, 0, 0, 4, 0, 0 };
for (int c = 2; c >= 0; c--)
{
b = f;
*g = k[c + 3];
k[c + 1] = 0;
}
for (int i = 0; i < 8; i++)
if (d[0][i][0] != 0)
__builtin_abort ();
return 0;
}
We can't tell no-alias info for pairs and . Is this expected or
should be improved?
Thanks
[Bug tree-optimization/94125] [9/10 Regression] wrong code at -O3 on x86_64-linux-gnu
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94125 Jakub Jelinek changed: What|Removed |Added Target Milestone|9.3 |9.4 --- Comment #6 from Jakub Jelinek --- GCC 9.3.0 has been released, adjusting target milestone.
[Bug tree-optimization/94125] [9/10 Regression] wrong code at -O3 on x86_64-linux-gnu
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94125 --- Comment #5 from bin cheng --- Thanks for CCing, I will have a look this WE.
[Bug tree-optimization/94125] [9/10 Regression] wrong code at -O3 on x86_64-linux-gnu
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94125
Richard Biener changed:
What|Removed |Added
CC||amker at gcc dot gnu.org
--- Comment #4 from Richard Biener ---
Hm, it computes a dependence distance of two and in the end sorts partitions
in the wrong order from a bogus partition dependence edge. The odd thing is
that for
for (int c = 0; c <= 2; c++)
{
b = f;
*g = k[c + 3];
k[c + 1] = 0;
}
we compute a distance of minus two (two + DDR_REVERSED_P) but in both
cases we need to use the same partition ordering, memset after the
partition containing the k[c+3] load but the partition dependence code
from the DDRs appearant different direction handles both cases differently.
Something is missing here. Not sure what - Bin, any idea?
[Bug tree-optimization/94125] [9/10 Regression] wrong code at -O3 on x86_64-linux-gnu
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94125 Richard Biener changed: What|Removed |Added Assignee|unassigned at gcc dot gnu.org |rguenth at gcc dot gnu.org Status|NEW |ASSIGNED Priority|P1 |P2 Known to work||8.3.0 --- Comment #3 from Richard Biener --- I'll have a look. Note the bisection point is a correctness fix only possibly resulting in less optimization.
[Bug tree-optimization/94125] [9/10 Regression] wrong code at -O3 on x86_64-linux-gnu
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94125 Jeffrey A. Law changed: What|Removed |Added CC||law at redhat dot com Priority|P3 |P1
[Bug tree-optimization/94125] [9/10 Regression] wrong code at -O3 on x86_64-linux-gnu
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94125 --- Comment #2 from Jakub Jelinek --- Seems it is the ldist pass, which fails to figure out that k[c+3] load in the loop might alias with the k[c+1] = 0; store and moves all the 3 stores into a memset after the loop.
[Bug tree-optimization/94125] [9/10 Regression] wrong code at -O3 on x86_64-linux-gnu
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94125 Jakub Jelinek changed: What|Removed |Added Ever confirmed|0 |1 Status|UNCONFIRMED |NEW Last reconfirmed||2020-03-10
[Bug tree-optimization/94125] [9/10 Regression] wrong code at -O3 on x86_64-linux-gnu
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94125
Jakub Jelinek changed:
What|Removed |Added
CC||jakub at gcc dot gnu.org
--- Comment #1 from Jakub Jelinek ---
Somewhat reduced testcase:
unsigned char b, f;
short d[1][8][1], *g = [0][3][0];
int
main ()
{
int k[] = { 0, 0, 0, 4, 0, 0 };
for (int c = 2; c >= 0; c--)
{
b = f;
*g = k[c + 3];
k[c + 1] = 0;
}
for (int i = 0; i < 8; i++)
if (d[0][i][0] != 0)
__builtin_abort ();
return 0;
}
[Bug tree-optimization/94125] [9/10 Regression] wrong code at -O3 on x86_64-linux-gnu
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94125 Andrew Pinski changed: What|Removed |Added Summary|wrong code at -O3 on|[9/10 Regression] wrong |x86_64-linux-gnu|code at -O3 on ||x86_64-linux-gnu Keywords||wrong-code Version|unknown |10.0 Target Milestone|--- |9.3
