Re: strub causing libgcc to fail to build on rl78-elf
On 12/6/23 15:03, DJ Delorie wrote:
Alexandre Oliva writes:
This looks like a latent bug in the port.
I'm not surprised, that port was weird.
This was just a plain asm insn in strub.c:
/* Make sure the stack overwrites are not optimized away. */
asm ("" : : "m" (end[0]));
whose constraint passes during reload, rl78_alloc_physical_registers
leaves it alone and clears virt_insns_ok, so when cprog_hardreg attempts
to extract constraints again, rl78_as_legitimate_address rejects r8 as
the address because virt insns are no longer ok.
Some background: the "virtual" registers are memory-mapped registers
that use a common addressing scheme to access non-mapped registers.
When we convert from virtual to physical, we can map that reg to a
physical reg, or we replace the reg with a mem, but then usually have to
split up the insn.
For this insn, "converting" should have mapped or reloaded r8 to a valid
address register. I doubt we have a way to have two patterns for user
asms like we do for, say, addhi3.
Given we don't know the semantics of what goes on inside the MEM I think
rewriting would be extraordinarily difficult. Ultimately all this feels
like a limited reload pass implemented in the rl78 backend. You'd have
to look at all the operands, potentially spill one or more values,
arrange for input/output reloads, deal with clobbers (particularly
reloading the address given (clobber (mem (addr))).
I suspect that something in the virt->phys logic just doesn't know how
to check for mem constraints in user asms.
I looked briefly, it appears the code just punts rewriting all user
asms, but maybe I missed something.
I wouldn't lose any sleep if we had a way to simply disable strub for rl78.
Jeff
Re: strub causing libgcc to fail to build on rl78-elf
Alexandre Oliva writes:
> This looks like a latent bug in the port.
I'm not surprised, that port was weird.
> This was just a plain asm insn in strub.c:
>
> /* Make sure the stack overwrites are not optimized away. */
> asm ("" : : "m" (end[0]));
>
> whose constraint passes during reload, rl78_alloc_physical_registers
> leaves it alone and clears virt_insns_ok, so when cprog_hardreg attempts
> to extract constraints again, rl78_as_legitimate_address rejects r8 as
> the address because virt insns are no longer ok.
Some background: the "virtual" registers are memory-mapped registers
that use a common addressing scheme to access non-mapped registers.
When we convert from virtual to physical, we can map that reg to a
physical reg, or we replace the reg with a mem, but then usually have to
split up the insn.
For this insn, "converting" should have mapped or reloaded r8 to a valid
address register. I doubt we have a way to have two patterns for user
asms like we do for, say, addhi3.
I suspect that something in the virt->phys logic just doesn't know how
to check for mem constraints in user asms.
> I'm not at all familiar with this port, and I don't know what was
> supposed to happen here, but ISTM that either physical registers should
> be allocated for asms, or non-B0 regs should be accepted in asms.
non-bank-zero registers aren't valid as real address registers, because
in gcc's reality they *are* mems. The chip can bank switch them, but
gcc doesn't (the interrupt handlers, being asm, can do so, which is why
one bank is reserved for that).
Re: strub causing libgcc to fail to build on rl78-elf
[adding gcc@]
Hi, Jeff,
On Dec 6, 2023, Jeff Law wrote:
> libgcc is currently failing to build on rl78, looks like it might be
> strub related.
Thanks for letting me know.
>> /home/jlaw/test/gcc/libgcc/strub.c:149:1: error: unrecognizable insn:
>> 149 | }
>> | ^
>> (insn 30 64 33 4 (asm_operands/v ("") ("") 0 [
>> (mem/f:HI (reg:HI 8 r8) [1 *base_8+0 S2 A16])
>> ]
>> [
>> (asm_input:HI ("m") /home/jlaw/test/gcc/libgcc/strub.c:147)
>> ]
>> [] /home/jlaw/test/gcc/libgcc/strub.c:147)
>> "/home/jlaw/test/gcc/libgcc/strub.c":147:3 -1
>> (expr_list:REG_DEAD (reg:HI 8 r8)
>> (nil)))
>> during RTL pass: cprop_hardreg
This looks like a latent bug in the port.
This was just a plain asm insn in strub.c:
/* Make sure the stack overwrites are not optimized away. */
asm ("" : : "m" (end[0]));
whose constraint passes during reload, rl78_alloc_physical_registers
leaves it alone and clears virt_insns_ok, so when cprog_hardreg attempts
to extract constraints again, rl78_as_legitimate_address rejects r8 as
the address because virt insns are no longer ok.
I'm not at all familiar with this port, and I don't know what was
supposed to happen here, but ISTM that either physical registers should
be allocated for asms, or non-B0 regs should be accepted in asms.
I don't see a maintainer listed for rl78; is there anyone familiar
enough with it to confirm (or dispute ;-) my suspicions, and discuss
possibilities to get this fixed?
DJ, AFAICT was you who contributed the port. Do you have any wisdom
about it to share?
TIA,
--
Alexandre Oliva, happy hackerhttps://FSFLA.org/blogs/lxo/
Free Software Activist GNU Toolchain Engineer
Disinformation flourishes because many people care deeply about injustice but
very few check the facts. Think Assange & Stallman. The empires strike back
