[llvm-commits] x86 branch sequence optimization in LLVM code gen: please review

[Chandler Carruth]

On Thu, Jan 5, 2012 at 1:53 AM, Umansky, Victor <victor.umansky at intel.com>wrote:

> Well, if it would be possible to change LLVM intrinsic prototype – then
> you’re right, no instruction combining were required.****
>
> However until this will be done in LLVM spec – the optimization is in
> place.
>

There is no spec, it is a change to LLVM's intrinsics, you can post a patch
to do this to this mailing list. =] You need to change the intrinsic
definition, update any code that reasons about that intrinsic, add
auto-upgrade logic to upgrade old IR inputs from the old intrinsic to the
new intrinsic, and teach the frontends to emit the new one. It's a fair
amount of code, but none of it hard.

Please don't leave bad code checked into the codegen layer. We need to fix
this the correct way if/when we find the correct way to fix it. Thus far,
updating the LLVM intrinsics is looking very promising.
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