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Re: Scheduling problem - A more detailed explain

ÎâêØ wrote:
Well... Is there anything I miss or forget to do ?

Someone needs to step through code in a debugger and try to figure out what is going wrong.

I made an initial attempt at that. I hacked gcc a little to try to force a failure with a contrived testcase. The first thing I noticed is that I pointed you at the wrong bit of code. The rws_access_reg code is used for placing stop bits, which is not the problem here. The problem here is in the scheduler. Unfortunately, this leads to a second problem. How this works in the scheduler depends on what gcc sources you are using. There is the pre-dataflow merge code and the post-dataflow merge code. I don't know which one you are using. From earlier comments, I'm guessing that you are using some snapshot from mid to early summer. It would be helpful to know exactly what sources you are starting from. Worst case, I might also need your gcc patches, if I can't find a way to trigger the failure on my own.

The scheduler dep code is in sched-deps.c. Try looking at sched_analyze_insn. As before, it does use hard_regno_nregs so in theory it should be working.

Do we know for sure that the scheduler is failing here? Have you looked at -da RTL dumps to verify which pass is performing the incorrect optimization?

Currently, gcc only emits these pr reg group save/restores in the prologue and epilogue, and we have scheduling barriers after/before the prologue/epilogue, so it is possible that there is a latent problem here which has gone unnoticed simply because it is impossible to reproduce with unmodified FSF gcc sources.
Jim Wilson, GNU Tools Support,

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