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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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Adds a new register allocator callback
Target:branch_preds(Instr, Context) which, for a control flow
instruction Instr, returns a list of tuples {Target, Probability} for
each label name Target that Instr may branch to. Probability is a float
between 0.0 and 1.0 and corresponds to the predicted probability that
control flow branches to the corresponding target. The probabilities may
sum to at most 1.0 (rounding errors aside). Note that a sum less than
1.0 is valid.
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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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This allows us to pass around the context data that
hipe_regalloc_prepass needs cleanly, without using process dictionary or
parameterised modules (like it was previous to this change).
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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_ppc_subst, was introduced to the ppc backend.
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Now that all backends do register allocation on a CFG directly and
define the defun_to_cfg/1 callback as the identity function, it can be
removed.
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hipe_regalloc_prepass speeds up register allocation by spilling any temp
that is live over a call (which clobbers all register).
In order to detect these, a new function was added to the target
interface; defines_all_alloc/1, that takes an instruction and returns a
boolean.
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Now, there will only ever be a single Linear->CFG conversion, just after
lowering from RTL, and only ever a single CFG->Linear conversion, just
before the finalise pass. Both of these now happen in hipe_ppc_main.
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