llvm dev - Feb 2013 - [LLVMdev] Instruction scheduling barrier

I found myself wanting a "scheduling barrier" in LLVM.  In my specific
circumstances I only want it to mean that
TargetInstrInfoImpl::isSchedulingBoundary() would return true.

I added SchedulingBarrier to MCID in MCInstrDesc.h and pushed it through TD
attributes down to isSchedulingBoundary().  Is this something of general
interest, or is there another mechanism for implementing barriers that I missed?


Thanks

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On Feb 26, 2013, at 4:01 PM, Mark Schimmel <Mark.Schimmel at synopsys.com>
wrote:
> I found myself wanting a “scheduling barrier” in LLVM.  In my specific
circumstances I only want it to mean that
TargetInstrInfoImpl::isSchedulingBoundary() would return true.
>  
> I added SchedulingBarrier to MCID in MCInstrDesc.h and pushed it through TD
attributes down to isSchedulingBoundary().  Is this something of general
interest, or is there another mechanism for implementing barriers that I missed?
 I don't think you need both a SchedulingBarrier MCID and a special
TargetInstrInfo hook. isSchedulingBoundary is a currently target hook because
it's fairly specific to a CodeGen pass, we want to make general queries here
like isTerminator and isCall, and the answer may vary depending on some
attribute of the function. You can always add a target specific barrier opcode
and check for it within the target hook without changing the MC API.

-Andy
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