[Bug tree-optimization/114192] scalar code left around following early break vectorization of reduction
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114192 --- Comment #5 from GCC Commits --- The master branch has been updated by Richard Biener : https://gcc.gnu.org/g:324d2907c86f05e40dc52d226940308f53a956c2 commit r14-9292-g324d2907c86f05e40dc52d226940308f53a956c2 Author: Richard Biener Date: Mon Mar 4 09:46:13 2024 +0100 tree-optimization/114192 - scalar reduction kept live with early break vect The following fixes a missing replacement of the reduction value used in the epilog, causing the scalar reduction to be kept live across the early break exit path. PR tree-optimization/114192 * tree-vect-loop.cc (vect_create_epilog_for_reduction): Use the appropriate def for the live out stmt in case of an alternate exit.
[Bug tree-optimization/114192] scalar code left around following early break vectorization of reduction
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114192 Richard Biener changed: What|Removed |Added Status|ASSIGNED|RESOLVED Resolution|--- |FIXED --- Comment #6 from Richard Biener --- Fixed.
[Bug tree-optimization/114192] scalar code left around following early break vectorization of reduction
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114192 --- Comment #4 from Richard Biener --- vect-early-break_104-pr113373.c might be such case which ICEs then.
[Bug tree-optimization/114192] scalar code left around following early break vectorization of reduction
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114192 --- Comment #3 from Richard Biener --- Created attachment 57600 --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=57600=edit patch Ah, so the issue is that we only replace the LHS, in this case we pass the reduction stmt for the early exit but the live value is defined by the PHI (we re-start the iteration). That confuses the replacement process. It looks like it might also be wrong for the peeled case on the main edge? The following fixes it for me. Didn't check what happens for the peeled case with a reduction.
[Bug tree-optimization/114192] scalar code left around following early break vectorization of reduction
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114192 Richard Biener changed: What|Removed |Added Assignee|unassigned at gcc dot gnu.org |rguenth at gcc dot gnu.org Status|NEW |ASSIGNED --- Comment #2 from Richard Biener --- The issue is the scalar reduction value is live from the main loop to the epilog. We don't seem to use the vector .REDUC_PLUS value on both paths. Likely failure of reduction epilog generation. Let me have a look.
[Bug tree-optimization/114192] scalar code left around following early break vectorization of reduction
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114192
Tamar Christina changed:
What|Removed |Added
Ever confirmed|0 |1
Status|UNCONFIRMED |NEW
Last reconfirmed||2024-03-01
--- Comment #1 from Tamar Christina ---
Confirmed.
It looks like DCE6 no longer thinks:
# sum_10 = PHI
_1 = aD.4432[i_12];
sum_7 = _1 + sum_11;
is dead after vectorization.
it removes the only dead consumer of sum_7,
a PHI node left over in the guard block which becomes unused after the
reduction is vectorized.
DCE says:
marking necessary through sum_11 stmt sum_11 = PHI
processing: sum_11 = PHI
marking necessary through sum_7 stmt sum_7 = _1 + sum_11;
processing: sum_7 = _1 + sum_11;
marking necessary through _1 stmt _1 = a[i_12];
processing: _1 = a[i_12];
so it thinks the closed definition is needed?
This seems to only happen with reductions, other live operations look fine:
extern int a[1024];
int f4(int *x, int n)
{
int sum = 0;
for (int i = 0; i < n; i++)
{
sum = a[i];
if (a[i] == 42)
break;
}
return sum;
}
