Re: [PATCH v2] rs6000: Add new pass for replacement of contiguous addresses vector load lxv with lxvp

["Kewen.Lin" <linkw@linux.ibm.com>]

on 2023/11/28 15:05, Michael Meissner wrote:
> I tried using this patch to compare with the vector size attribute patch I
> posted.  I could not build it as a cross compiler on my x86_64 because the
> assembler gives the following error:
> 
> Error: operand out of domain (11 is not a multiple of 2) for
> std_stacktrace-elf.o.  If you look at the assembler, it has combined a lxvp 11
> and lxvp 12 into:
> 
>         lxvp 11,0(9)
> 
> The powerpc architecture requires that registers that are loaded with load
> vector pair and stored with store vector point instructions only load/store
> even/odd register pairs, and not odd/even pairs.  Unfortunately, it will mean
> that this optimization will match less often.
> 

Yes, the current implementation need some refinements, as comments in [1]:

> Besides, it seems a bad idea to put this pass after reload? as register allocation
> finishes, this pairing has to be restricted by the reg No. (I didn't see any
> checking on the reg No. relationship for paring btw.)
> 
> Looking forward to the comments from Segher/David/Peter/Mike etc.

I wonder if we should consider running such pass before reload instead.

[1] https://gcc.gnu.org/pipermail/gcc-patches/2023-November/638070.html

BR,
Kewen