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Re: Compact regsiter allocation

Jamie Prescott <> writes:

>> Normally gcc will allocate registers in the order they are listed in
>> REG_ALLOC_ORDER, which defaults to increasing numeric order.  gcc won't
>> normally allocate register sparsely.  That said, it is quite possible
>> for gcc to allocate a register and then discover that it need not be
>> allocated.  There isn't currently any way to request that gcc tighten up
>> the register allocation.  That would probably require another
>> optimization pass to consistently rename registers when there is a hole
>> in the allocation order.
> Yep, usually it allocates compact, but I noticed that when there's some inline assembly
> with ad-hoc register naming, it starts generating holes.
> The extra renaming pass, is it something available today?


> If not, what is the best spot (in the normal GCC target hooks) to trigger it? Where the
> full insn tree is passed in such hook (if it's not a global)?

TARGET_MACHINE_DEPENDENT_REORG.  It will be invoked once for each
function, and can access and modify the complete RTL insn tree.


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