https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64172
--- Comment #13 from Vladimir Makarov <vmakarov at gcc dot gnu.org> ---
I've investigated the generated code. The problem is in IRA live-range
splitting on the region borders. The pseudo to consider is 157 which contains
local_prng.d in the following code
void randmemset (prng_t *prng, uint8_t *buf, size_t size)
{
prng_t local_prng = *prng;
....
while (size > 0)
{
uint32_t e = local_prng.p0.a - ((local_prng.p0.b << 27) +
(local_prng.p0.b >> (32 - 27)));
local_prng.p0.a = local_prng.p0.b ^ ((local_prng.p0.c << 17) ^
(local_prng.p0.c >> (32 - 17)));
local_prng.p0.b = local_prng.p0.c + local_prng.p0.d;
local_prng.p0.c = local_prng.p0.d + e;
local_prng.p0.d = e + local_prng.p0.a;
*buf++ = local_prng.p0.d;
size--;
}
=> *prng = local_prng;
}
The pseudo gets different hard regs in different regions
Disposition:
...
8:r155 l0 mem 40:r157 l1 8 25:r157 l2 6 6:r157 l0 4
...
In the loop above, it gets 6, outside the loop it gets 4. On the exit from the
loop, IRA generates
157:TI = 308:TI
308 is created from 157 to be used in the loop.
The insn is split on 4 insns:
449: r157:TI#0=r308:TI#0
450: r157:TI#4=r308:TI#4
451: r157:TI#8=r308:TI#8
452: r157:TI#12=r308:TI#12
In order words, in terms of hard regs we do 6<-4; 7<-5; 8<-6; 9<-7. The two
last insns use wrong values.
I'll think how to fix it better. I hope that the fix will be ready at the end
of next week.
