GCC Middle and Back End API Reference
resource.c File Reference

Data Structures

struct  target_info


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 ()


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

Function Documentation

void clear_hashed_info_for_insn ( )
   Clear any hashed information that we have stored for INSN.  
static int find_basic_block ( rtx  ,

Referenced by return_insn_p().

static int find_basic_block ( )
   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
     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.  
static rtx find_dead_or_set_registers ( rtx  target,
struct resources res,
rtx jump_target,
int  jump_count,
struct resources  set,
struct resources  needed 
   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
             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
     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
void mark_referenced_resources ( rtx  x,
struct resources res,
bool  include_delayed_effects 
   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
     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
         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
         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 
   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.

static rtx next_insn_no_annul ( rtx  )
static rtx next_insn_no_annul ( )
   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.  
static bool return_insn_p ( )
static void update_live_status ( rtx  ,
const_rtx  ,
void *   
static void update_live_status ( )
   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().

Variable Documentation

int* bb_ticks
   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

Referenced by init_resource_info(), and mark_target_live_regs().

HARD_REG_SET current_live_regs
   Marks registers possibly live at the current place being scanned by
   mark_target_live_regs.  Also used by update_live_status.  
struct resources end_of_function_needs
   Indicates what resources are required at function end.  

Referenced by return_insn_p().

HARD_REG_SET pending_dead_regs
   Marks registers for which we have seen a REG_DEAD note but no assignment.
   Also only used by the next two functions.  
struct resources start_of_epilogue_needs
   Indicates what resources are required at the beginning of the epilogue.  
struct target_info** target_hash_table = NULL
   Define the hash table itself.