- Generated by
1.8.1.1
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GCC Middle and Back End API Reference
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Data Structures | |
| struct | target_info |
Functions | |
| static void | update_live_status (rtx, const_rtx, void *) |
| static int | find_basic_block (rtx, int) |
| static rtx | next_insn_no_annul (rtx) |
| static rtx | find_dead_or_set_registers (rtx, struct resources *, rtx *, int, struct resources, struct resources) |
| static void | update_live_status () |
| static int | find_basic_block () |
| static rtx | next_insn_no_annul () |
| void | mark_referenced_resources (rtx x, struct resources *res, bool include_delayed_effects) |
| void | mark_set_resources (rtx x, struct resources *res, int in_dest, enum mark_resource_type mark_type) |
| static bool | return_insn_p () |
| void | mark_target_live_regs () |
| void | init_resource_info () |
| void | free_resource_info () |
| void | clear_hashed_info_for_insn () |
| void | incr_ticks_for_insn () |
| void | mark_end_of_function_resources () |
Variables | |
| static struct resources | start_of_epilogue_needs |
| static struct resources | end_of_function_needs |
| static struct target_info ** | target_hash_table = NULL |
| static int * | bb_ticks |
| static HARD_REG_SET | current_live_regs |
| static HARD_REG_SET | pending_dead_regs |
| void clear_hashed_info_for_insn | ( | ) |
Clear any hashed information that we have stored for INSN.
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Referenced by return_insn_p().
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Find the number of the basic block with correct live register information that starts closest to INSN. Return -1 if we couldn't find such a basic block or the beginning is more than SEARCH_LIMIT instructions before INSN. Use SEARCH_LIMIT = -1 for an unlimited search. The delay slot filling code destroys the control-flow graph so, instead of finding the basic block containing INSN, we search backwards toward a BARRIER where the live register information is correct.
Scan backwards to the previous BARRIER. Then see if we can find a
label that starts a basic block. Return the basic block number. The closest BARRIER is too far away.
The start of the function.
See if any of the upcoming CODE_LABELs start a basic block. If we reach
anything other than a CODE_LABEL or note, we can't find this code.
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A subroutine of mark_target_live_regs. Search forward from TARGET looking for registers that are set before they are used. These are dead. Stop after passing a few conditional jumps, and/or a small number of unconditional branches.
If this instruction can throw an exception, then we don't
know where we might end up next. That means that we have to
assume that whatever we have already marked as live really is
live. After a label, any pending dead registers that weren't yet
used can be made dead. If INSN is a USE made by update_block, we care about the
underlying insn. Any registers set by the underlying insn
are live since the insn is being done somewhere else. All other USE insns are to be ignored.
An unconditional jump can be used to fill the delay slot
of a call, so search for a JUMP_INSN in any position. We can handle conditional branches here by following
both paths, and then IOR the results of the two paths
together, which will give us registers that are dead
on both paths. Since this is expensive, we give it
a much higher cost than unconditional branches. The
cost was chosen so that we will follow at most 1
conditional branch. For an annulled branch, mark_set_resources ignores slots
filled by instructions from the target. This is correct
if the branch is not taken. Since we are following both
paths from the branch, we must also compute correct info
if the branch is taken. We do this by inverting all of
the INSN_FROM_TARGET_P bits, calling mark_set_resources,
and then inverting the INSN_FROM_TARGET_P bits again. Don't try this optimization if we expired our jump count
above, since that would mean there may be an infinite loop
in the function being compiled.
References mark_set_resources(), and MARK_SRC_DEST_CALL.
| void free_resource_info | ( | void | ) |
Free up the resources allocated to mark_target_live_regs (). This should be invoked after the last call to mark_target_live_regs ().
| void incr_ticks_for_insn | ( | ) |
Increment the tick count for the basic block that contains INSN.
| void init_resource_info | ( | ) |
Initialize the resources required by mark_target_live_regs (). This should be invoked before the first call to mark_target_live_regs.
Indicate what resources are required to be valid at the end of the current
function. The condition code never is and memory always is.
The stack pointer is needed unless EXIT_IGNORE_STACK is true
and there is an epilogue that restores the original stack pointer
from the frame pointer. Registers used to return the function value
are needed. Registers holding global variables are needed. The registers required to be live at the end of the function are
represented in the flow information as being dead just prior to
reaching the end of the function. For example, the return of a value
might be represented by a USE of the return register immediately
followed by an unconditional jump to the return label where the
return label is the end of the RTL chain. The end of the RTL chain
is then taken to mean that the return register is live.
This sequence is no longer maintained when epilogue instructions are
added to the RTL chain. To reconstruct the original meaning, the
start of the epilogue (NOTE_INSN_EPILOGUE_BEG) is regarded as the
point where these registers become live (start_of_epilogue_needs).
If epilogue instructions are present, the registers set by those
instructions won't have been processed by flow. Thus, those
registers are additionally required at the end of the RTL chain
(end_of_function_needs). Allocate and initialize the tables used by mark_target_live_regs.
Set the BLOCK_FOR_INSN of each label that starts a basic block.
References bb_ticks, free(), and target_info::next.
| void mark_end_of_function_resources | ( | ) |
Add TRIAL to the set of resources used at the end of the current function.
Given X, some rtl, and RES, a pointer to a `struct resource', mark which resources are referenced by the insn. If INCLUDE_DELAYED_EFFECTS is TRUE, resources used by the called routine will be included for CALL_INSNs.
Handle leaf items for which we set resource flags. Also, special-case
CALL, SET and CLOBBER operators. If this memory shouldn't change, it really isn't referencing
memory. Mark registers used to access memory.
Traditional asm's are always volatile.
For all ASM_OPERANDS, we must traverse the vector of input operands.
We can not just fall through here since then we would be confused
by the ASM_INPUT rtx inside ASM_OPERANDS, which do not indicate
traditional asms unlike their normal usage. The first operand will be a (MEM (xxx)) but doesn't really reference
memory. The second operand may be referenced, though. Usually, the first operand of SET is set, not referenced. But
registers used to access memory are referenced. SET_DEST is
also referenced if it is a ZERO_EXTRACT. A CALL references memory, the frame pointer if it exists, the
stack pointer, any global registers and any registers given in
USE insns immediately in front of the CALL.
However, we may have moved some of the parameter loading insns
into the delay slot of this CALL. If so, the USE's for them
don't count and should be skipped. If we are part of a delay slot sequence, point at the SEQUENCE.
Check for a REG_SETJMP. If it exists, then we must
assume that this call can need any register.
This is done to be more conservative about how we handle setjmp.
We assume that they both use and set all registers. Using all
registers ensures that a register will not be considered dead
just because it crosses a setjmp call. A register should be
considered dead only if the setjmp call returns nonzero. ... fall through to other INSN processing ...
In addition to the usual references, also consider all outputs
as referenced, to compensate for mark_set_resources treating
them as killed. This is similar to ZERO_EXTRACT / STRICT_LOW_PART
handling, execpt that we got a partial incidence instead of a partial
width. No special processing, just speed up.
Process each sub-expression and flag what it needs.
Referenced by resource_conflicts_p(), return_insn_p(), and try_merge_delay_insns().
| void mark_set_resources | ( | rtx | x, |
| struct resources * | res, | ||
| int | in_dest, | ||
| enum mark_resource_type | mark_type | ||
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Given X, a part of an insn, and a pointer to a `struct resource', RES, indicate which resources are modified by the insn. If MARK_TYPE is MARK_SRC_DEST_CALL, also mark resources potentially set by the called routine. If IN_DEST is nonzero, it means we are inside a SET. Otherwise, objects are being referenced instead of set. We never mark the insn as modifying the condition code unless it explicitly SETs CC0 even though this is not totally correct. The reason for this is that we require a SET of CC0 to immediately precede the reference to CC0. So if some other insn sets CC0 as a side-effect, we know it cannot affect our computation and thus may be placed in a delay slot.
These don't set any resources.
Called routine modifies the condition code, memory, any registers
that aren't saved across calls, global registers and anything
explicitly CLOBBERed immediately after the CALL_INSN. Check for a REG_SETJMP. If it exists, then we must
assume that this call can clobber any register. ... and also what its RTL says it modifies, if anything.
An insn consisting of just a CLOBBER (or USE) is just for flow
and doesn't actually do anything, so we ignore it. If the source of a SET is a CALL, this is actually done by
the called routine. So only include it if we are to include the
effects of the calling routine. Traditional asm's are always volatile.
For all ASM_OPERANDS, we must traverse the vector of input operands.
We can not just fall through here since then we would be confused
by the ASM_INPUT rtx inside ASM_OPERANDS, which do not indicate
traditional asms unlike their normal usage. Process each sub-expression and flag what it needs.
Referenced by check_annul_list_true_false(), find_dead_or_set_registers(), insn_references_resource_p(), and try_merge_delay_insns().
| void mark_target_live_regs | ( | ) |
Set the resources that are live at TARGET. If TARGET is zero, we refer to the end of the current function and can return our precomputed value. Otherwise, we try to find out what is live by consulting the basic block information. This is tricky, because we must consider the actions of reload and jump optimization, which occur after the basic block information has been computed. Accordingly, we proceed as follows:: We find the previous BARRIER and look at all immediately following labels (with no intervening active insns) to see if any of them start a basic block. If we hit the start of the function first, we use block 0. Once we have found a basic block and a corresponding first insn, we can accurately compute the live status (by starting at a label following a BARRIER, we are immune to actions taken by reload and jump.) Then we scan all insns between that point and our target. For each CLOBBER (or for call-clobbered regs when we pass a CALL_INSN), mark the appropriate registers are dead. For a SET, mark them as live. We have to be careful when using REG_DEAD notes because they are not updated by such things as find_equiv_reg. So keep track of registers marked as dead that haven't been assigned to, and mark them dead at the next CODE_LABEL since reload and jump won't propagate values across labels. If we cannot find the start of a basic block (should be a very rare case, if it can happen at all), mark everything as potentially live. Next, scan forward from TARGET looking for things set or clobbered before they are used. These are not live. Because we can be called many times on the same target, save our results in a hash table indexed by INSN_UID. This is only done if the function init_resource_info () was invoked before we are called.
Handle end of function.
Handle return insn.
We have to assume memory is needed, but the CC isn't.
See if we have computed this value already.
Start by getting the basic block number. If we have saved
information, we can get it from there unless the insn at the
start of the basic block has been deleted. If the information is up-to-date, use it. Otherwise, we will
update it below. Allocate a place to put our results and chain it into the
hash table. If we found a basic block, get the live registers from it and update
them with anything set or killed between its start and the insn before
TARGET; this custom life analysis is really about registers so we need
to use the LR problem. Otherwise, we must assume everything is live. Compute hard regs live at start of block.
Get starting and ending insn, handling the case where each might
be a SEQUENCE. If this insn is from the target of a branch, it isn't going to
be used in the sequel. If it is used in both cases, this
test will not be true. If this insn is a USE made by update_block, we care about the
underlying insn. Values in call-clobbered registers survive a COND_EXEC CALL
if that is not executed; this matters for resoure use because
they may be used by a complementarily (or more strictly)
predicated instruction, or if the CALL is NORETURN. CALL clobbers all call-used regs that aren't fixed except
sp, ap, and fp. Do this before setting the result of the
call live. A CALL_INSN sets any global register live, since it may
have been modified by the call. Mark anything killed in an insn to be deadened at the next
label. Ignore USE insns; the only REG_DEAD notes will be for
parameters. But they might be early. A CALL_INSN will usually
clobber registers used for parameters. It isn't worth bothering
with the unlikely case when it won't. If any registers were unused after this insn, kill them.
These notes will always be accurate. A label clobbers the pending dead registers since neither
reload nor jump will propagate a value across a label. We must conservatively assume that all registers that used
to be live here still are. The fallthrough edge may have
left a live register uninitialized. The beginning of the epilogue corresponds to the end of the
RTL chain when there are no epilogue insns. Certain resources
are implicitly required at that point. We didn't find the start of a basic block. Assume everything
in use. This should happen only extremely rarely. If we hit an unconditional branch, we have another way of finding out
what is live: we can see what is live at the branch target and include
anything used but not set before the branch. We add the live
resources found using the test below to those found until now. Include JUMP_INSN in the needed registers.
References target_info::bb_tick, bb_ticks, target_info::block, target_info::live_regs, and resources::regs.
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Similar to next_insn, but ignores insns in the delay slots of an annulled branch.
If INSN is an annulled branch, skip any insns from the target
of the branch.
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Return TRUE if INSN is a return, possibly with a filled delay slot.
References target_info::block, resources::cc, end_of_function_needs, find_basic_block(), mark_referenced_resources(), resources::memory, target_info::next, scratch, target_info::uid, and resources::volatil.
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Utility function called from mark_target_live_regs via note_stores. It deadens any CLOBBERed registers and livens any SET registers.
References subreg_nregs(), and subreg_regno().
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For each basic block, we maintain a generation number of its basic block info, which is updated each time we move an insn from the target of a jump. This is the generation number indexed by block number.
Referenced by init_resource_info(), and mark_target_live_regs().
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Marks registers possibly live at the current place being scanned by mark_target_live_regs. Also used by update_live_status.
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Indicates what resources are required at function end.
Referenced by return_insn_p().
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Marks registers for which we have seen a REG_DEAD note but no assignment. Also only used by the next two functions.
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Indicates what resources are required at the beginning of the epilogue.
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Define the hash table itself.
1.8.1.1