llvm dev - Jun 2012 - [LLVMdev] generating pass timing info in a JIT context

Our project runs LLVM in a JIT context, and we want to explore where the time is
being spent in the various LLVM components.  At the moment, we're running
with a production version of 3.0, and expecting to upgrade to 3.1 soon.  We
noticed that clang and llc can display component timing using the -ftime-passes
and -time-passes options respectively.  A little poking around in the code
revealed that the timers are started by setting the variable
"TimePassesIsEnabled" to true - that's how the command line
processing code does it.

However, setting this variable in the JIT context fails to elicit the timer
information coming out on stderr.  :-(

Earlier, I implemented an optional statistics display using calls to
"EnableStatistics()" and "PrintStatistics()" at appropriate
places in the JIT environment.  This uses the same output file control mechanism
as the timing info, and works fine.  The difference is that the
"PrintStatistics()" function is global - it knows about all the
statistics being kept.   The output to stderr works fine.

The equivalent printing control for the timing info is, however, bound to the
TimerGroup class implemented in Support/Timer.h, .cpp.   The relevant TimerGroup
structures are static to the modules that define them, so there is no
possibility of forcing the printing, like I can do with Statistics.  :-(

I haven't yet resorted to debugging LLVM in the JIT context to figure out
what's going wrong, and I haven't had good luck with this approach in
the past, so if anyone has a clue what I'm doing wrong, I'd appreciate
hearing from you.  Thanks in advance,
        -Kevin Harris
        Unisys

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