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These pseudo instructions are added to all backends and allow spill slot
to spill slot move coalescing in a clean way.
They have regular move semantics, but contain an additional scratch
register to be used if both source and destination are spilled, and can
not be move coalesced.
Additionally, a register allocator callback
Target:is_spill_move(Instr, Context) is added which allows the spill
slot allocators to check for these instructions and try to coalesce the
spill slots the two temporaries are allocated to.
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In addition to the temporary name rewriting that hipe_regalloc_prepass
does, range splitters also need to be able to insert move instructions,
as well as inserting new basic blocks in the control flow graph. The
following four callbacks are added for that purpose:
* Target:mk_move(Src, Dst, Context)
Returns a move instruction from the temporary (not just register
number) Src to Dst.
* Target:mk_goto(Label, Context)
Returns a unconditional control flow instruction that branches to the
label with name Label.
* Target:redirect_jmp(Instr, ToOld, ToNew, Context)
Modifies the control flow instruction Instr so that any control flow
that would go to a label with name ToOld instead goes to the label
with name ToNew.
* Target:new_label(Context)
Returns a fresh label name that does not belong to any existing block
in the current function, and is to be used to create a new basic
block in the control flow graph by calling Target:update_bb/4 with
this new name.
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These will not only be useful for hipe_regalloc_prepass, but also, after
the introduction of a mk_move/2 (or similar) callback, for the purpose
of range splitting.
Since the substitution needed to case over all the instructions, a new
module, hipe_arm_subst, was introduced to the arm backend.
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