Alexander Monakov wrote:
Hi.
I have two questions related to register allocation and reload area.
1. Is there a way to distinguish memory accesses introduced during
register allocation (register spills and fills) from "regular" ones?
Or, alternatively, is augmenting reload & friends to use specific
instructions to perform spill&fill possible? I'm asking because on
ia64 one must use special instructions to read/write registers that
originate from control-speculative load (in case speculation was
unsuccessful, such registers will have an attribute, called NaT bit,
set, and it must be saved and restored properly when such register is
spilled), so currently GCC cannot perform control speculation before
register allocation on ia64.
You can differ spill slots from other stack memory. All spill slots are
generated in reload1::alter_reg. It is called at the start of
reload1::reload for pseudo-registers got memory (their reg_renumber is
negative) and during reload work when the reload needs a hard register
and has to spill a pseudo-register assigned to the hard register during
local/global alloc. This pseudo-register is spilled and getting memory
from alter_reg. In the last case, a simple sharing stack slots has been
implemented (based on a hard-register assigned to the pseudo before
spilling).
2. Is there a way to ask register allocator to allocate same hard regs
for given pseudo in given pair of insns? I assume the answer is 'no',
but just in case :) Again, this is needed to support data speculation
before register allocation: register that is speculatively loaded must
be same for speculative load and check.
Currently the same pseudo-register always get the same hard-register (or
memory). The current register allocator does not support register live
range splitting.
