Re: [PATCH, ARM, LRA] Fixed bootstrap failure in Thumb mode

[Jeff Law <law at redhat dot com>]

On 11/27/13 10:58, Vladimir Makarov wrote:
> > The secondary reload macros/hooks define cases where additional
> > registers are needed to reload certain forms of rtl.  I doubt the use
> > of LRA completely eliminates the need for secondary reloads.
>    When I designed LRA I wanted to remove as many hooks as possible
> because I thought insn constraints as major info source are enough.
> Unfortunately I did not succeed fully with secondary reload hooks and
> macros.  It is still needed for some complicated cases but general rule
> to port LRA to a target is to try to switch these hooks off.
I should have remembered some of this.  Didn't we discuss this in the 
context of SECONDARY_MEMORY_NEEDED?


>    For example, LRA can generate a move of pseudos of classes for which
> hardware has no real insn.  After that looking on the move constraints,
> LRA can generate more move insns and additional pseudos to generate
> moves (loads or stores if additional pseudos got NO_REGS) which
> represent real hardware insns.  In complicated cases when these macros
> are still needed, LRA runs into infinite loop of such move generation if
> the macros are not used.
So it sounds like LRA reduces the need for the SECONDARY_RELOAD_* 
hooks/macros, but doesn't totally eliminate them.

So I find myself wondering if/how we can document this in the manual. 
Vlad, can you take a stab at that.


>    I might be return to a project to remove necessity of such hooks and
> macros for LRA but I am not sure when.  I guess I need to write a small
> guidance too how to port LRA.
That would be good as well, but I think most folks doing port work refer 
more to the GCC internals manual, so we certainly need it updated in 
addition to any "how to port to LRA" kind of document.

Jeff