[LLVMdev] clang -O2 versus opt -O2 | llc | clang

[Tim Northover]

>> I've not tracked down quite how Clang sets that extra
>> "-unroll-runtime" option (I'd be interested to know myself, actually,
>> having failed).
>
> It doesn't, but the backend can by overriding TTI::getUnrollingPreferences
> or setting LoopMicroOpBufferSize in the processor scheduling model.

I don't think that explains what I'm seeing either: only PPC and R600
seem to mention that function. All code I'm compiling is x86_64.

Cheers.

Tim.

(Incidentally, "opt -loop-unroll -unroll-runtime" may need an already
optimised .ll file. I'm attaching my copy here in case it helps
anyone).
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