haifa-scheduler marks instructions having TRUE dependencies as an ANTI dependencies.

[Viktor Pobedin]

Hi all,

It seems that sometimes haifa-scheduler assigns ANTI dependency for the
instructions having TRUE dependency. 

I observed it happening in case of basic block as following:
<32 memory load/store rtx>
rtx_1: store to memory
rtx_2: load from memory

I1 and i2 will have ANTI dependency instead of TRUE dependency.

Once the sizes of pending_read_insns and pending_write_insns is bigger than
MAX_PENDING_LIST_LENGTH (32) the sched_analyze_1 does flush_pending_lists
thus putting current insn (rtx_1 in this example) to the
last_pending_memory_flush list. During the analysis of the next rtx (rtx_2
in the example) sched_analyze_2 marks rtx_1 and rtx_2  as having ANTI
dependence. This is done in sched-deps.c:2652 by the following code:
for (u = deps->last_pending_memory_flush; u; u = XEXP
(u, 1))
  add_dependence (insn, XEXP (u, 0), REG_DEP_ANTI);


I have few questions with this regard:
1.  Is my understanding correct? 
2.  If it is what is the reason for this behavior?
3.  What should I do in the cost_adjust hook if I want to distinguish
between two cases (TRUE and ANTI dependency). In my target the cost for
anti-dependency is 0, and cost for the true dependency 1 or bigger.

BR, Viktor.

converting rtx object to the assembly instruction.

[Viktor Pobedin]

Is there a simple way to convert rtx object to the assemble 
insutruction? Ideally I would like to have function something like:

const char *rtx2asm(rtx insn);
returning a string with the asm instruction for the insn.

Closest thing that I found is the final_scan_insn function in final.c 
but unfortunatelly it outputs the asm string to the file so it makes it 
not usefull for my purposes.


Thanks, Viktor.

Re: converting rtx object to the assembly instruction.

[Viktor Pobedin]

 On 8/13/2013 10:37 PM, Richard Sandiford wrote:

Viktor Pobedin  writes:

Is there a simple way to convert rtx object to the assemble
insutruction? Ideally I would like to have function something like:
  const char *rtx2asm(rtx insn);
returning a string with the asm instruction for the insn.

Closest thing that I found is the final_scan_insn function in final.c
but unfortunatelly it outputs the asm string to the file so it makes it
not usefull for my purposes.

Yeah, I'm afraid that's all there is.

Richard


 Richard,

 Thanks for the clarification. I found a relative easy way to implement
 this function by redirecting the FILE to char. Posting it here, maybe
 someone else will find it usefull:

 char *rtx2asm(rtx insn)
 {
  static char *bp;
  size_t size;
  int seen = 0;
  FILE *tmp = asm_out_file;
  asm_out_file = open_memstream(&bp, &size);
  final_scan_insn (insn, asm_out_file, 0, 0 , &seen);
  fflush (asm_out_file);
  asm_out_file = tmp;
  bp[strlen(bp)-1] = 0;
  return bp;
 }



 BR, Viktor.