- Generated by
1.8.1.1
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GCC Middle and Back End API Reference
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Data Structures | |
| struct | stack_def |
| struct | block_info_def |
Typedefs | |
| typedef struct stack_def * | stack_ptr |
| typedef struct block_info_def * | block_info |
Enumerations | |
| enum | emit_where { EMIT_AFTER, EMIT_BEFORE } |
Variables | |
| static vec< char > | stack_regs_mentioned_data |
| int | regstack_completed = 0 |
| static basic_block | current_block |
| static bool | starting_stack_p |
| static rtx | FP_mode_reg [LAST_STACK_REG+1-FIRST_STACK_REG][(int) MAX_MACHINE_MODE] |
| static rtx | not_a_num |
| static rtx | ix86_flags_rtx |
| static bool | any_malformed_asm |
| typedef struct block_info_def * block_info |
This is used to carry information about basic blocks. It is attached to the AUX field of the standard CFG block.
This is the basic stack record. TOP is an index into REG[] such that REG[TOP] is the top of stack. If TOP is -1 the stack is empty. If TOP is -2, REG[] is not yet initialized. Stack initialization consists of placing each live reg in array `reg' and setting `top' appropriately. REG_SET indicates which registers are live.
| enum emit_where |
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Select the better of two edges E1 and E2 to use to determine the stack layout for their shared destination basic block. This is typically the more frequently executed. The edge E1 may be NULL (in which case E2 is returned), but E2 is always non-NULL.
Prefer critical edges to minimize inserting compensation code on
critical edges. Avoid non-deterministic behavior.
Referenced by convert_regs_entry().
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Change the organization of the stack so that it fits a new basic block. Some registers might have to be popped, but there can never be a register live in the new block that is not now live. Insert any needed insns before or after INSN, as indicated by WHERE. OLD is the original stack layout, and NEW is the desired form. OLD is updated to reflect the code emitted, i.e., it will be the same as NEW upon return. This function will not preserve block_end[]. But that information is no longer needed once this has executed.
Stack adjustments for the first insn in a block update the
current_block's stack_in instead of inserting insns directly.
compensate_edges will add the necessary code later. We will be inserting new insns "backwards". If we are to insert
after INSN, find the next insn, and insert before it. Initialize partially dead variables.
Pop any registers that are not needed in the new block.
If the destination block's stack already has a specified layout
and contains two or more registers, use a more intelligent algorithm
to pop registers that minimizes the number number of fxchs below. First pass to determine the free slots.
Second pass to allocate preferred slots.
If this is a preference for the new top of stack, record
the fact by remembering it's old->reg in topsrc. Intentionally, avoid placing the top of stack in it's correct
location, if we still need to permute the stack below and we
can usefully place it somewhere else. This is the case if any
slot is still unallocated, in which case we should place the
top of stack there. Third pass allocates remaining slots and emits pop insns.
Find next free slot.
The following loop attempts to maximize the number of times we
pop the top of the stack, as this permits the use of the faster
ffreep instruction on platforms that support it. If the new block has never been processed, then it can inherit
the old stack order. This block has been entered before, and we must match the
previously selected stack order. By now, the only difference should be the order of the stack,
not their depth or liveliness. If the stack is not empty (new_stack->top != -1), loop here emitting
swaps until the stack is correct.
The worst case number of swaps emitted is N + 2, where N is the
depth of the stack. In some cases, the reg at the top of
stack may be correct, but swapped anyway in order to fix
other regs. But since we never swap any other reg away from
its correct slot, this algorithm will converge. Swap the reg at top of stack into the position it is
supposed to be in, until the correct top of stack appears. See if any regs remain incorrect. If so, bring an
incorrect reg to the top of stack, and let the while loop
above fix it. At this point there must be no differences.
References emit_swap_insn(), stack_def::reg, and stack_def::top.
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There are many rules that an asm statement for stack-like regs must follow. Those rules are explained at the top of this file: the rule numbers below refer to that explanation.
Find out what the constraints require. If no constraint
alternative matches, this asm is malformed. Avoid further trouble with this insn.
Strip SUBREGs here to make the following code simpler.
Set up CLOBBER_REG.
Enforce rule #4: Output operands must specifically indicate which
reg an output appears in after an asm. "=f" is not allowed: the
operand constraints must select a class with a single reg.
Also enforce rule #5: Output operands must start at the top of
the reg-stack: output operands may not "skip" a reg. Search for first non-popped reg.
If there are any other popped regs, that's an error.
Enforce rule #2: All implicitly popped input regs must be closer
to the top of the reg-stack than any input that is not implicitly
popped. An input reg is implicitly popped if it is tied to an
output, or if there is a CLOBBER for it. Search for first non-popped reg.
If there are any other popped regs, that's an error.
Enforce rule #3: If any input operand uses the "f" constraint, all
output constraints must use the "&" earlyclobber.
??? Detect this more deterministically by having constrain_asm_operands
record any earlyclobber. Avoid further trouble with this insn.
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Handle a comparison. Special care needs to be taken to avoid causing comparisons that a 387 cannot do correctly, such as EQ. Also, a pop insn may need to be emitted. The 387 does have an `fcompp' insn that can pop two regs, but it is sometimes too expensive to do this - a `fcomp' followed by a `fstpl %st(0)' may be easier to set up.
??? If fxch turns out to be cheaper than fstp, give priority to
registers that die in this insn - move those to stack top first. We will fix any death note later.
If the second operand dies, handle that. But if the operands are
the same stack register, don't bother, because only one death is
needed, and it was just handled. As a special case, two regs may die in this insn if src2 is
next to top of stack and the top of stack also dies. Since
we have already popped src1, "next to top of stack" is really
at top (FIRST_STACK_REG) now. The 386 can only represent death of the first operand in
the case handled above. In all other cases, emit a separate
pop and remove the death note from here.
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Adjust the stack of edge E's source block on exit to match the stack of it's target block upon input. The stack layouts of both blocks should have been defined by now.
Check whether stacks are identical.
Abnormal calls may appear to have values live in st(0), but the
abnormal return path will not have actually loaded the values. Assert that the lifetimes are as we expect -- one value
live at st(0) on the end of the source block, and no
values live at the beginning of the destination block.
For complex return values, we may have st(1) live as well. Handle non-call EH edges specially. The normal return path have
values in registers. These will be popped en masse by the unwind
library. We don't support abnormal edges. Global takes care to
avoid any live register across them, so we should never
have to insert instructions on such edges. Make a copy of source_stack as change_stack is destructive.
It is better to output directly to the end of the block
instead of to the edge, because emit_swap can do minimal
insn scheduling. We can do this when there is only one
edge out, and it is not abnormal. ??? change_stack needs some point to emit insns after.
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Traverse all non-entry edges in the CFG, and emit the necessary edge compensation code to change the stack from stack_out of the source block to the stack_in of the destination block.
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Traverse all basic blocks in a function, converting the register references in each insn from the "flat" register file that gcc uses, to the stack-like registers the 387 uses.
Initialize uninitialized registers on function entry.
Construct the desired stack for function exit.
??? Future: process inner loops first, and give them arbitrary
initial stacks which emit_swap_insn can modify. This ought to
prevent double fxch that often appears at the head of a loop. Process all blocks reachable from all entry points.
??? Process all unreachable blocks. Though there's no excuse
for keeping these even when not optimizing. We must fix up abnormal edges before inserting compensation code
because both mechanisms insert insns on edges.
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Convert stack register references in one block. Return true if the CFG has been modified in the process.
Choose an initial stack layout, if one hasn't already been chosen.
Select the best incoming edge (typically the most frequent) to
use as a template for this basic block. No predecessors. Create an arbitrary input stack.
Process all insns in this block. Keep track of NEXT so that we
don't process insns emitted while substituting in INSN. Ensure we have not missed a block boundary.
Don't bother processing unless there is a stack reg
mentioned or if it's a CALL_INSN. Nothing must ever die at a debug insn. If something
is referenced in it that becomes dead, it should have
died before and the reference in the debug insn
should have been removed so as to avoid changing code
generation. Since it's the first non-debug instruction that determines
the stack requirements of the current basic block, we refrain
from updating debug insns before it in the loop above, and
fix them up here. If the function is declared to return a value, but it returns one
in only some cases, some registers might come live here. Emit
necessary moves for them. Amongst the insns possibly deleted during the substitution process above,
might have been the only trapping insn in the block. We purge the now
possibly dead EH edges here to avoid an ICE from fixup_abnormal_edges,
called at the end of convert_regs. The order in which we process the
blocks ensures that we never delete an already processed edge.
Note that, at this point, the CFG may have been damaged by the emission
of instructions after an abnormal call, which moves the basic block end
(and is the reason why we call fixup_abnormal_edges later). So we must
be sure that the trapping insn has been deleted before trying to purge
dead edges, otherwise we risk purging valid edges.
??? We are normally supposed not to delete trapping insns, so we pretend
that the insns deleted above don't actually trap. It would have been
better to detect this earlier and avoid creating the EH edge in the first
place, still, but we don't have enough information at that time. Something failed if the stack lives don't match. If we had malformed
asms, we zapped the instruction itself, but that didn't produce the
same pattern of register kills as before.
References edge_def::dest.
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Convert registers in all blocks reachable from BLOCK. Return true if the CFG has been modified in the process.
We process the blocks in a top-down manner, in a way such that one block
is only processed after all its predecessors. The number of predecessors
of every block has already been computed. Processing BLOCK is achieved by convert_regs_1, which may purge
some dead EH outgoing edge after the deletion of the trapping
insn inside the block. Since the number of predecessors of
BLOCK's successors was computed based on the initial edge set,
we check the necessity to process some of these successors
before such an edge deletion may happen. However, there is
a pitfall: if BLOCK is the only predecessor of a successor and
the edge between them happens to be deleted, the successor
becomes unreachable and should not be processed. The problem
is that there is no way to preventively detect this case so we
stack the successor in all cases and hand over the task of
fixing up the discrepancy to convert_regs_1.
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This function was doing life analysis. We now let the regular live code do it's job, so we only need to check some extra invariants that reg-stack expects. Primary among these being that all registers are initialized before use. The function returns true when code was emitted to CFG edges and commit_edge_insertions needs to be called.
Load something into each stack register live at function entry.
Such live registers can be caused by uninitialized variables or
functions not returning values on all paths. In order to keep
the push/pop code happy, and to not scrog the register stack, we
must put something in these registers. Use a QNaN.
Note that we are inserting converted code here. This code is
never seen by the convert_regs pass.
References change_stack(), EMIT_BEFORE, emit_note(), end_sequence(), get_insns(), insert_insn_on_edge(), and start_sequence().
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Construct the desired stack for function exit. This will either be `empty', or the function return value at top-of-stack.
Referenced by move_for_stack_reg(), remove_regno_note(), subst_stack_regs_in_debug_insn(), and swap_to_top().
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Emit an insn to pop virtual register REG before or after INSN. REGSTACK is the stack state after INSN and is updated to reflect this pop. WHEN is either emit_insn_before or emit_insn_after. A pop insn is represented as a SET whose destination is the register to be popped and source is the top of stack. A death note for the top of stack cases the movdf pattern to pop.
For complex types take care to pop both halves. These may survive in
CLOBBER and USE expressions.
References get_hard_regnum(), i1, limit, stack_def::reg, stack_regs_mentioned(), and stack_def::top.
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Emit an insn before or after INSN to swap virtual register REG with the top of stack. REGSTACK is the stack state before the swap, and is updated to reflect the swap. A swap insn is represented as a PARALLEL of two patterns: each pattern moves one reg to the other. If REG is already at the top of the stack, no insn is emitted.
Something failed if the register wasn't on the stack. If we had
malformed asms, we zapped the instruction itself, but that didn't
produce the same pattern of register sets as before. To prevent
further failure, adjust REGSTACK to include REG at TOP. Find the previous insn involving stack regs, but don't pass a
block boundary. If the previous register stack push was from the reg we are to
swap with, omit the swap. If the previous insn wrote to the reg we are to swap with,
omit the swap. Avoid emitting the swap if this is the first register stack insn
of the current_block. Instead update the current_block's stack_in
and let compensate edges take care of this for us.
Referenced by change_stack().
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Calculate the number of inputs and outputs in BODY, an asm_operands. N_OPERANDS is the total number of operands, and N_INPUTS and N_OUTPUTS are pointers to ints into which the results are placed.
Referenced by emit_pop_insn(), remove_regno_note(), subst_all_stack_regs_in_debug_insn(), and swap_to_top().
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Find the hard register number of virtual register REG in REGSTACK. The hard register number is relative to the top of the stack. -1 is returned if the register is not found.
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Return a pointer to the REG expression within PAT. If PAT is not a REG, possible enclosed by a conversion rtx, return the inner part of PAT that stopped the search.
Eliminate FP subregister accesses in favor of the
actual FP register in use.
| rtl_opt_pass* make_pass_stack_regs | ( | ) |
| rtl_opt_pass* make_pass_stack_regs_run | ( | ) |
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Handle a move to or from a stack register in PAT, which is in INSN. REGSTACK is the current stack. Return whether a control flow insn was deleted in the process.
Write from one stack reg to another. If SRC dies here, then
just change the register mapping and delete the insn. If this is a no-op move, there must not be a REG_DEAD note.
The destination must be dead, or life analysis is borked.
If the source is not live, this is yet another case of
uninitialized variables. Load up a NaN instead. It is possible that the dest is unused after this insn.
If so, just pop the src. The source reg does not die.
If this appears to be a no-op move, delete it, or else it
will confuse the machine description output patterns. But if
it is REG_UNUSED, we must pop the reg now, as per-insn processing
for REG_UNUSED will not work for deleted insns. The destination ought to be dead.
Save from a stack reg to MEM, or possibly integer reg. Since
only top of stack may be saved, emit an exchange first if
needs be. A 387 cannot write an XFmode value to a MEM without
clobbering the source reg. The output code can handle
this by reading back the value from the MEM.
But it is more efficient to use a temp register if one is
available. Push the source value here if the register
stack is not full, and then write the value to memory via
a pop. Load from MEM, or possibly integer REG or constant, into the
stack regs. The actual target is always the top of the
stack. The stack mapping is changed to reflect that DEST is
now at top of stack. The destination ought to be dead. However, there is a
special case with i387 UNSPEC_TAN, where destination is live
(an argument to fptan) but inherent load of 1.0 is modelled
as a load from a constant.
References control_flow_insn_p(), delete_insn(), EMIT_AFTER, emit_pop_insn(), and find_regno_note().
Referenced by subst_all_stack_regs_in_debug_insn(), and swap_to_top().
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A helper function which replaces INSN with a pattern that loads up a NaN into DEST, then invokes move_for_stack_reg.
References reg_mentioned_p().
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Search forward looking for the first use of this value.
Stop at block boundaries.
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Pop a register from the stack.
If regno was not at the top of stack then adjust stack.
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Print stack configuration.
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Copy the stack info from the end of edge E's source block to the start of E's destination block.
Preserve the order of the original stack, but check whether
any pops are needed. Push in any partially dead values.
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Convert register usage from "flat" register file usage to a "stack register file. FILE is the dump file, if used. Construct a CFG and run life analysis. Then convert each insn one by one. Run a last cleanup_cfg pass, if optimizing, to eliminate code duplication created when the converter inserts pop insns on the edges.
Clean up previous run.
See if there is something to do. Flow analysis is quite
expensive so we might save some compilation time. Set up block info for each basic block.
Set current register status at last instruction `uninitialized'.
Copy live_at_end and live_at_start into temporaries.
Create the replacement registers up front.
A QNaN for initializing uninitialized variables.
??? We can't load from constant memory in PIC mode, because
we're inserting these instructions before the prologue and
the PIC register hasn't been set up. In that case, fall back
on zero, which we can get from `fldz'. Allocate a cache for stack_regs_mentioned.
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Remove a note of type NOTE, which must be found, for register number REGNO from INSN. Remove only one such note.
References emit_pop_insn(), and get_hard_regnum().
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Referenced by subst_stack_regs_in_debug_insn().
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Replace REG, which is a pointer to a stack reg RTX, with an RTX for the desired hard REGNO.
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Convert register usage from flat register file usage to a stack register file.
| int stack_regs_mentioned | ( | ) |
Return nonzero if INSN mentions stacked registers, else return zero.
Allocate some extra size to avoid too many reallocs, but
do not grow too quickly. This insn has yet to be examined. Do so now.
Referenced by emit_pop_insn().
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Forward declarations
Referenced by stack_regs_mentioned_p().
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Return nonzero if any stack register is mentioned somewhere within PAT.
References stack_regs_mentioned_p().
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If current function returns its result in an fp stack register, return the REG. Otherwise, return 0.
If the value is supposed to be returned in memory, then clearly
it is not returned in a stack register.
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Reorganize the stack into ascending numbers, before this insn.
If there is only a single register on the stack, then the stack is
already in increasing order and no reorganization is needed.
Similarly if the stack is empty.
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Substitute hardware stack regs in debug insn INSN, using stack layout REGSTACK. If we can't find a hardware stack reg for any of the REGs in it, reset the debug insn.
References emit_insn_before(), get_hard_regnum(), and move_nan_for_stack_reg().
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Substitute hard regnums for any stack regs in INSN, which has N_INPUTS inputs and N_OUTPUTS outputs. REGSTACK is the stack info before the insn, and is updated with changes made here. There are several requirements and assumptions about the use of stack-like regs in asm statements. These rules are enforced by record_asm_stack_regs; see comments there for details. Any asm_operands left in the RTL at this point may be assume to meet the requirements, since record_asm_stack_regs removes any problem asm.
Find out what the constraints required. If no constraint
alternative matches, that is a compiler bug: we should have caught
such an insn in check_asm_stack_operands. Strip SUBREGs here to make the following code simpler.
Set up NOTE_REG, NOTE_LOC and NOTE_KIND.
Set up CLOBBER_REG and CLOBBER_LOC.
Put the input regs into the desired place in TEMP_STACK.
If an operand needs to be in a particular reg in
FLOAT_REGS, the constraint was either 't' or 'u'. Since
these constraints are for single register classes, and
reload guaranteed that operand[i] is already in that class,
we can just use REGNO (recog_data.operand[i]) to know which
actual reg this operand needs to be in. recog_data.operand[i] is not in the right place. Find
it and swap it with whatever is already in I's place.
K is where recog_data.operand[i] is now. J is where it
should be. Emit insns before INSN to make sure the reg-stack is in the right
order. Make the needed input register substitutions. Do death notes and
clobbers too, because these are for inputs, not outputs. It's OK for a CLOBBER to reference a reg that is not live.
Don't try to replace it in that case. Sigh - clobbers always have QImode. But replace_reg knows
that these regs can't be MODE_INT and will assert. Just put
the right reg there without calling replace_reg. Now remove from REGSTACK any inputs that the asm implicitly popped.
An input reg is implicitly popped if it is tied to an
output, or if there is a CLOBBER for it. recog_data.operand[i] might not be at the top of stack.
But that's OK, because all we need to do is pop the
right number of regs off of the top of the reg-stack.
record_asm_stack_regs guaranteed that all implicitly
popped regs were grouped at the top of the reg-stack. Now add to REGSTACK any outputs that the asm implicitly pushed.
Note that there isn't any need to substitute register numbers.
??? Explain why this is true. See if there is an output for this hard reg.
Now emit a pop insn for any REG_UNUSED output, or any REG_DEAD
input that the asm didn't implicitly pop. If the asm didn't
implicitly pop an input reg, that reg will still be live.
Note that we can't use find_regno_note here: the register numbers
in the death notes have already been substituted.
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Substitute stack hard reg numbers for stack virtual registers in INSN. Non-stack register numbers are not changed. REGSTACK is the current stack content. Insns may be emitted as needed to arrange the stack for the 387 based on the contents of the insn. Return whether a control flow insn was deleted in the process.
If there are any floating point parameters to be passed in
registers for this call, make sure they are in the right
order. Now mark the arguments as dead after the call.
Do the actual substitution if any stack regs are mentioned.
Since we only record whether entire insn mentions stack regs, and
subst_stack_regs_pat only works for patterns that contain stack regs,
we must check each pattern in a parallel here. A call_value_pop could
fail otherwise. This insn is an `asm' with operands. Decode the operands,
decide how many are inputs, and do register substitution.
Any REG_UNUSED notes will be handled by subst_asm_stack_regs. subst_stack_regs_pat may have deleted a no-op insn. If so, any
REG_UNUSED will already have been dealt with, so just return. If this a noreturn call, we can't insert pop insns after it.
Instead, reset the stack state to empty. If there is a REG_UNUSED note on a stack register on this insn,
the indicated reg must be popped. The REG_UNUSED note is removed,
since the form of the newly emitted pop insn references the reg,
making it no longer `unset'.
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Substitute new registers in LOC, which is part of a debug insn. REGSTACK is the current register layout.
If we can't find an active register, reset this debug insn.
References EMIT_BEFORE, emit_pop_insn(), find_reg_note(), remove_note(), and replace_reg().
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Substitute new registers in PAT, which is part of INSN. REGSTACK is the current register layout. Return whether a control flow insn was deleted in the process.
Deaths in USE insns can happen in non optimizing compilation.
Handle them by popping the dying register. USEs are ignored for liveness information so USEs of dead
register might happen. Uninitialized USE might happen for functions returning uninitialized
value. We will properly initialize the USE on the edge to EXIT_BLOCK,
so it is safe to ignore the use here. This is consistent with behavior
of dataflow analyzer that ignores USE too. (This also imply that
forcibly initializing the register to NaN here would lead to ICE later,
since the REG_DEAD notes are not issued.) The fix_truncdi_1 pattern wants to be able to
allocate its own scratch register. It does this by
clobbering an fp reg so that it is assured of an
empty reg-stack register. If the register is live,
kill it now. Remove the DEAD/UNUSED note so we
don't try to kill it later too.
In reality the UNUSED note can be absent in some
complicated cases when the register is reused for
partially set variable. A top-level clobber with no REG_DEAD, and no hard-regnum
indicates an uninitialized value. Because reload removed
all other clobbers, this must be due to a function
returning without a value. Load up a NaN. See if this is a `movM' pattern, and handle elsewhere if so.
This is a `tstM2' case.
Fall through.
These insns only operate on the top of the stack. DEST might
be cc0_rtx if we're processing a tstM pattern. Also, it's
possible that the tstM case results in a REG_DEAD note on the
source. On i386, reversed forms of subM3 and divM3 exist for
MODE_FLOAT, so the same code that works for addM3 and mulM3
can be used. These insns can accept the top of stack as a destination
from a stack reg or mem, or can use the top of stack as a
source and some other stack register (possibly top of stack)
as a destination. We will fix any death note later.
If either operand is not a stack register, then the dest
must be top of stack. Both operands are REG. If neither operand is already
at the top of stack, choose to make the one that is the
dest the new top of stack. If the source is not live, this is yet another case of
uninitialized variables. Load up a NaN instead. If the register that dies is at the top of stack, then
the destination is somewhere else - merely substitute it.
But if the reg that dies is not at top of stack, then
move the top of stack to the dead reg, as though we had
done the insn and then a store-with-pop. Keep operand 1 matching with destination.
These insns only operate on the top of the stack.
This insn only operate on the top of the stack.
Above insns operate on the top of the stack.
Above insns operate on the top two stack slots,
first part of one input, double output insn. Input should never die, it is replaced with output.
These insns operate on the top two stack slots,
second part of one input, double output insn. FALLTHRU
For UNSPEC_TAN, regstack->top is already increased
by inherent load of constant 1.0. Output value is generated in the second stack slot.
Move current value from second slot to the top. These insns operate on the top two stack slots.
Pop both input operands from the stack.
Push the result back onto the stack.
These insns operate on the top two stack slots,
first part of double input, double output insn. Inputs should never die, they are
replaced with outputs. Push the result back onto stack. Empty stack slot
will be filled in second part of insn. These insns operate on the top two stack slots,
second part of double input, double output insn. Push the result back onto stack. Fill empty slot from
first part of insn and fix top of stack pointer. This insn operates on the top two stack slots,
third part of C2 setting double input insn. (unspec [(unspec [(compare)] UNSPEC_FNSTSW)] UNSPEC_SAHF)
The combination matches the PPRO fcomi instruction. Fall through.
Combined fcomp+fnstsw generated for doing well with
CSE. When optimizing this would have been broken
up before now. This insn requires the top of stack to be the destination.
If the comparison operator is an FP comparison operator,
it is handled correctly by compare_for_stack_reg () who
will move the destination to the top of stack. But if the
comparison operator is not an FP comparison operator, we
have to handle it here. In case one of operands is the top of stack and the operands
dies, it is safe to make it the destination operand by
reversing the direction of cmove and avoid fxch. Make reg-stack believe that the operands are already
swapped on the stack Reverse condition to compensate the operand swap.
i386 do have comparison always reversible. If the register that dies is not at the top of
stack, then move the top of stack to the dead reg.
Top of stack should never die, as it is the
destination. Make dest the top of stack. Add dest to regstack if
not present.
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We're looking for a single set to cc0 or an HImode temporary.
See if this is, or ends in, a fnstsw. If so, we're not doing anything
with the cc value right now. We may be able to search for one
though. Search forward looking for the first use of this value.
Stop at block boundaries. We haven't found it.
So we've found the insn using this value. If it is anything
other than sahf or the value does not die (meaning we'd have
to search further), then we must give up. Now we are prepared to handle this as a normal cc0 setter.
In case the flags don't die here, recurse to try fix
following user too.
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Swap the condition on a branch, if there is one. Return true if we found a condition to swap. False if the condition was not used as such.
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Emit an insns before INSN to swap virtual register SRC1 with the top of stack and virtual register SRC2 with second stack slot. REGSTACK is the stack state before the swaps, and is updated to reflect the swaps. A swap insn is represented as a PARALLEL of two patterns: each pattern moves one reg to the other. If SRC1 and/or SRC2 are already at the right place, no swap insn is emitted.
Place operand 1 at the top of stack.
Place operand 2 next on the stack.
References control_flow_insn_p(), delete_insn(), EMIT_AFTER, emit_pop_insn(), find_regno_note(), get_hard_regnum(), move_nan_for_stack_reg(), stack_def::reg, stack_def::reg_set, and stack_def::top.
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Set if we find any malformed asms in a block.
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The block we're currently working on.
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This is the register file for all register after conversion.
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Used to initialize uninitialized registers.
| int regstack_completed = 0 |
Nonzero after end of regstack pass. Set to 1 or 0 by reg-stack.c.
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@verbatim
Register to Stack convert for GNU compiler. Copyright (C) 1992-2013 Free Software Foundation, Inc.
This file is part of GCC.
GCC is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 3, or (at your option) any later version.
GCC is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.
You should have received a copy of the GNU General Public License along with GCC; see the file COPYING3. If not see http://www.gnu.org/licenses/.
This pass converts stack-like registers from the "flat register
file" model that gcc uses, to a stack convention that the 387 uses.
* The form of the input:
On input, the function consists of insn that have had their
registers fully allocated to a set of "virtual" registers. Note that
the word "virtual" is used differently here than elsewhere in gcc: for
each virtual stack reg, there is a hard reg, but the mapping between
them is not known until this pass is run. On output, hard register
numbers have been substituted, and various pop and exchange insns have
been emitted. The hard register numbers and the virtual register
numbers completely overlap - before this pass, all stack register
numbers are virtual, and afterward they are all hard.
The virtual registers can be manipulated normally by gcc, and their
semantics are the same as for normal registers. After the hard
register numbers are substituted, the semantics of an insn containing
stack-like regs are not the same as for an insn with normal regs: for
instance, it is not safe to delete an insn that appears to be a no-op
move. In general, no insn containing hard regs should be changed
after this pass is done.
* The form of the output:
After this pass, hard register numbers represent the distance from
the current top of stack to the desired register. A reference to
FIRST_STACK_REG references the top of stack, FIRST_STACK_REG + 1,
represents the register just below that, and so forth. Also, REG_DEAD
notes indicate whether or not a stack register should be popped.
A "swap" insn looks like a parallel of two patterns, where each
pattern is a SET: one sets A to B, the other B to A.
A "push" or "load" insn is a SET whose SET_DEST is FIRST_STACK_REG
and whose SET_DEST is REG or MEM. Any other SET_DEST, such as PLUS,
will replace the existing stack top, not push a new value.
A store insn is a SET whose SET_DEST is FIRST_STACK_REG, and whose
SET_SRC is REG or MEM.
The case where the SET_SRC and SET_DEST are both FIRST_STACK_REG
appears ambiguous. As a special case, the presence of a REG_DEAD note
for FIRST_STACK_REG differentiates between a load insn and a pop.
If a REG_DEAD is present, the insn represents a "pop" that discards
the top of the register stack. If there is no REG_DEAD note, then the
insn represents a "dup" or a push of the current top of stack onto the
stack.
* Methodology:
Existing REG_DEAD and REG_UNUSED notes for stack registers are
deleted and recreated from scratch. REG_DEAD is never created for a
SET_DEST, only REG_UNUSED.
* asm_operands:
There are several rules on the usage of stack-like regs in
asm_operands insns. These rules apply only to the operands that are
stack-like regs:
1. Given a set of input regs that die in an asm_operands, it is
necessary to know which are implicitly popped by the asm, and
which must be explicitly popped by gcc.
An input reg that is implicitly popped by the asm must be
explicitly clobbered, unless it is constrained to match an
output operand.
2. For any input reg that is implicitly popped by an asm, it is
necessary to know how to adjust the stack to compensate for the pop.
If any non-popped input is closer to the top of the reg-stack than
the implicitly popped reg, it would not be possible to know what the
stack looked like - it's not clear how the rest of the stack "slides
up".
All implicitly popped input regs must be closer to the top of
the reg-stack than any input that is not implicitly popped.
3. It is possible that if an input dies in an insn, reload might
use the input reg for an output reload. Consider this example:
asm ("foo" : "=t" (a) : "f" (b));
This asm says that input B is not popped by the asm, and that
the asm pushes a result onto the reg-stack, i.e., the stack is one
deeper after the asm than it was before. But, it is possible that
reload will think that it can use the same reg for both the input and
the output, if input B dies in this insn.
If any input operand uses the "f" constraint, all output reg
constraints must use the "&" earlyclobber.
The asm above would be written as
asm ("foo" : "=&t" (a) : "f" (b));
4. Some operands need to be in particular places on the stack. All
output operands fall in this category - there is no other way to
know which regs the outputs appear in unless the user indicates
this in the constraints.
Output operands must specifically indicate which reg an output
appears in after an asm. "=f" is not allowed: the operand
constraints must select a class with a single reg.
5. Output operands may not be "inserted" between existing stack regs.
Since no 387 opcode uses a read/write operand, all output operands
are dead before the asm_operands, and are pushed by the asm_operands.
It makes no sense to push anywhere but the top of the reg-stack.
Output operands must start at the top of the reg-stack: output
operands may not "skip" a reg.
6. Some asm statements may need extra stack space for internal
calculations. This can be guaranteed by clobbering stack registers
unrelated to the inputs and outputs.
Here are a couple of reasonable asms to want to write. This asm
takes one input, which is internally popped, and produces two outputs.
asm ("fsincos" : "=t" (cos), "=u" (sin) : "0" (inp));
This asm takes two inputs, which are popped by the fyl2xp1 opcode,
and replaces them with one output. The user must code the "st(1)"
clobber for reg-stack.c to know that fyl2xp1 pops both inputs.
asm ("fyl2xp1" : "=t" (result) : "0" (x), "u" (y) : "st(1)"); We use this array to cache info about insns, because otherwise we spend too much time in stack_regs_mentioned_p. Indexed by insn UIDs. A value of zero is uninitialized, one indicates the insn uses stack registers, two indicates the insn does not use stack registers.
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In the current_block, whether we're processing the first register stack or call instruction, i.e. the regstack is currently the same as BLOCK_INFO(current_block)->stack_in.
1.8.1.1