On Thu, Jul 4, 2013 at 4:25 PM, Viktor Pobedin <viktor.pobe...@gmail.com> wrote: > 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?
Possibly a bug. > 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. >
