https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67808
Bug ID: 67808
Summary: LRA ICEs on simple double to long double conversion
test case
Product: gcc
Version: 6.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: target
Assignee: unassigned at gcc dot gnu.org
Reporter: bergner at gcc dot gnu.org
Target Milestone: ---
During a conversion from double to long double, LRA ends up going into a
infinite loop spilling things until it hits a threshold and quits with an ICE.
The simplest test case I have at the moment is:
bergner@genoa:~/gcc/BUGS/LRA/20011123-1$ cat bug2.i
void
foo (long double *ldb1, double *db1)
{
*ldb1 = *db1;
}
bergner@genoa:~/gcc/BUGS/LRA/20011123-1$
/home/bergner/gcc/build/gcc-fsf-mainline-bootstrap-lra-default-debug/gcc/xgcc
-B/home/bergner/gcc/build/gcc-fsf-mainline-bootstrap-lra-default-debug/gcc/ -S
-O1 -mvsx -S bug2.i
bug2.i: In function âfooâ:
bug2.i:5:1: internal compiler error: Max. number of generated reload insns per
insn is achieved (90)
}
^
0x10962903 lra_constraints(bool)
/home/bergner/gcc/gcc-fsf-mainline-bootstrap-lra-default/gcc/lra-constraints.c:4351
0x10942af7 lra(_IO_FILE*)
/home/bergner/gcc/gcc-fsf-mainline-bootstrap-lra-default/gcc/lra.c:2298
0x108c0ac7 do_reload
/home/bergner/gcc/gcc-fsf-mainline-bootstrap-lra-default/gcc/ira.c:5391
0x108c1183 execute
/home/bergner/gcc/gcc-fsf-mainline-bootstrap-lra-default/gcc/ira.c:5562
After IRA, things are pretty simple, with just the following one insn which
needs
a reload/spill, since we don't have memory to memory ops on POWER:
(insn 7 4 10 2 (parallel [
(set (mem:TF (reg:DI 3 3 [ ldb1 ]) [0 *ldb1_5(D)+0 S16 A128])
(float_extend:TF (mem:DF (reg:DI 4 4 [ db1 ]) [0 *db1_2(D)+0 S8
A64])))
(use (const_double:DF 0.0 [0x0.0p+0]))
]) bug2.i:4 445 {*extenddftf2_internal}
(expr_list:REG_DEAD (reg:DI 4 4 [ db1 ])
(expr_list:REG_DEAD (reg:DI 3 3 [ ldb1 ])
(nil))))
In LRA, comes along and gives us the following which looks good:
(insn 7 4 11 2 (parallel [
(set (reg:TF 159)
(float_extend:TF (mem:DF (reg:DI 4 4 [ db1 ]) [0 *db1_2(D)+0 S8
A64])))
(use (const_double:DF 0.0 [0x0.0p+0]))
]) bug2.i:4 445 {*extenddftf2_internal}
(expr_list:REG_DEAD (reg:DI 4 4 [ db1 ])
(expr_list:REG_DEAD (reg:DI 3 3 [ ldb1 ])
(nil))))
(insn 11 7 10 2 (set (mem:TF (reg:DI 3 3 [ ldb1 ]) [0 *ldb1_5(D)+0 S16 A128])
(reg:TF 159)) bug2.i:4 435 {*movtf_64bit_dm}
(nil))
But reg 159 was allocated to a VSX_REG and we don't have a TFmode mov* pattern
for vsx_reg -> fp_reg copy so we try to copy thru memory which is where we
started, so we loop forever until we hit the reload limit and ICE.
