H.J. Lu wrote:
> When reload gets:
>
> (insn 588 587 589 28 (set (mem:DF (zero_extend:DI (plus:SI (subreg:SI
> (reg/v/f:DI 182 [ b ]) 0)
> (const_int 8 [0x8]))) [4 MEM[base: b_96(D), index:
> D.15020_278, step: 8, offset: 0B]+0 S8 A64])
> (reg:DF 340 [ D.14980 ])) spooles.c:291 106
> {*movdf_internal_rex64}
> (expr_list:REG_DEAD (reg:DF 340 [ D.14980 ])
> (nil)))
Reloading of PLUS expressions is a long-standing problem. gen_reload
supports those only for PLUSes that look more or less like address
computations, and then only the "usual" cases.
Is the address above (once the pseudo reg:DI 182 is replaced by
a hard reg) really a legitimate address on your platform? If not,
this would need to be fixed at some earlier place.
If this *is* a valid address (and just not valid for this particular
insn pattern), the back-end needs to provide some means to reload to
allow reloading of such expressions. This can be done either by
providing an insn (plus post-reload splitter if necessary), or else
defining a secondary reload to handle the case where additional
registers are required. Assuming the generic gen_reload code is
powerful enough to handle complex expressions like this is probably
not wise ...
In any case, however, gen_reload should not generate *wrong*
code, so there's indeed a bug here.
However, this:
> - if (CONSTANT_P (op1) || MEM_P (op1) || GET_CODE (op1) == SUBREG
> + if ((GET_CODE (op0) != SUBREG
> + && (CONSTANT_P (op1) || MEM_P (op1)))
> + || GET_CODE (op1) == SUBREG
> || (REG_P (op1)
> && REGNO (op1) >= FIRST_PSEUDO_REGISTER)
> || (code != CODE_FOR_nothing
doesn't look like the proper fix for all cases. The actual problem
here is that this part of gen_reload takes the approach to transform
out <- op0 + op1
into
out <- op0
out <- out + op1
which is invalid if writing to out clobbers op1.
This means that:
- The "if" testing whether to swap op0 and op1 should verify
!reg_overlap_mentioned_p (out, op0)
- Regardless of whether we swapped or not, there needs to be a
gcc_assert (!reg_overlap_mentioned_p (out, op1));
before the gen_reload (out, op0, opnum, type) line.
There may still be cases where the algorithm of gen_reload doesn't
work, but at least we'll get an ICE instead of wrong code now.
Those cases will have to be fixed by the back-end as described
above ...
Bye,
Ulrich
--
Dr. Ulrich Weigand
GNU Toolchain for Linux on System z and Cell BE
ulrich.weig...@de.ibm.com
