Hi Zdenek, Hi Daniel, Hi Geoff,
I think that I have found a small bug in the loop invariant code.
The problem is exhibited when building newlib for the xstormy16-elf
toolchain although it may happen with other targets as well. The
problem occurs when an insn contains an r-value use of a register
that is going to hoisted as well as a clobber of that register, like
this:
(parallel [
(set (pc)
(if_then_else (lt:SI (reg:SI 45) <---
(reg:SI 26))
(label_ref:HI 129)
(pc)))
(clobber (reg:SI 45)) <-- must be the same
(clobber (scratch:BI))
])
The important point here is that the register referenced in the
first clobber must match the register used as the first argument of
the condition operation. (This comes from the "ineqbranchsi"
pattern in the xstormy16 machine description).
The problem is that the loop-invariant optimization was deciding
that (reg:SI 45) could be hoisted out of the loop, whereas really it
should be left alone. I have been looking at the loop invariant
code trying to figure out what needs to be changed, but so far I
have not been able to puzzle it out.
I think that the real problem might be the clobbers in the
ineqbranchsi pattern, but I do not know how it could be changed to
fix this.
Any ideas ?
Cheers
Nick
