[llvm-dev] [cfe-dev] Disable memset synthesis

Reid Kleckner via llvm-dev
Wed, 16 Aug 2017 17:38:35 -0000

On Tue, Aug 15, 2017 at 9:37 PM, Tim Northover via cfe-dev <
cfe-dev at lists.llvm.org> wrote:

> On 15 August 2017 at 19:38, bharathi seshadri via llvm-dev
> <llvm-dev at lists.llvm.org> wrote:
> > I find that GCC has an option -fno-tree-loop-distribute-patterns that
> > can be used to disable memcpy/memset synthesis. I wonder if there is
> > something similar in llvm/clang.
>
> I have no idea what that means, but we almost certainly don't have any
> option with similar semantics. Clang does not provide options to
> control specific optimization passes like that.
>

I think Sony exposes an option to disable idiom recognition in PS4
compiler. This seems like one of those areas where users keep asking for
something and we keep insisting that what they think they want isn't
actually what they want, i.e. disabling idiom recognition blocks mid-level
canonicalization and that leads to missing optimizations and bad
performance, etc. However, the user feedback has been persistent, and in
the interests of not having to hear about it again, we might want to
consider giving users the rope they need to hang themselves. It would let
them work around real performance problems today rather than waiting for
the next version of the compiler that will lower memset/memcpy/memcmp
better.
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