https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112999
Bug ID: 112999
Summary: riscv: Infinite loop with mask extraction
Product: gcc
Version: 14.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: target
Assignee: unassigned at gcc dot gnu.org
Reporter: rdapp at gcc dot gnu.org
CC: juzhe.zhong at rivai dot ai, pan2.li at intel dot com
Target Milestone: ---
Target: riscv
Pan Li found the following problematic case in his "full-coverage" testing and
I'm just documenting it here for reference.
/* { dg-do compile } */
/* { dg-options "-march=rv64gcv_zvl512b -mabi=lp64d
--param=riscv-autovec-lmul=m8 --param=riscv-autovec-preference=fixed-vlmax -O3
-fno-vect-cost-model -fno-tree-loop-distribute-patterns" } */
int a[1024];
int b[1024];
_Bool
fn1 ()
{
_Bool tem;
for (int i = 0; i < 1024; ++i)
{
tem = !a[i];
b[i] = tem;
}
return tem;
}
We try to extract the last bit from a 128-bit value of a mask vector. In order
to do so we first subreg by a tieable vector mode (here RVVMF4QI) then, because
we do not have a RVVMF4QI -> BI vector extraction, try type punning with a
TImode subreg.
As we do not natively support TImode, the result needs to be subreg'd again to
DImode. In the course of doing so we get lost in subreg moves and hit an
infinite loop. I have not tracked down the real root cause but the problem is
fixed by providing a movti pattern and special casing subreg:TI extraction from
vectors (just like we do in legitimize_move for other scalar subregs of vectors
- and wich I don't particularly like either :) ).
