[llvm] r293799 - [IPSCCP] Don't propagate return values of functions marked as noinline.

Davide Italiano via llvm-commits llvm-commits at lists.llvm.org
Wed Feb 1 16:33:57 PST 2017

On Wed, Feb 1, 2017 at 4:06 PM, Friedman, Eli <efriedma at codeaurora.org> wrote:
> On 2/1/2017 10:52 AM, Davide Italiano via llvm-commits wrote:
>> Author: davide
>> Date: Wed Feb  1 12:52:20 2017
>> New Revision: 293799
>> URL: http://llvm.org/viewvc/llvm-project?rev=293799&view=rev
>> Log:
>> [IPSCCP] Don't propagate return values of functions marked as noinline.
>> This tries to address what Hal defined (in the post-commit review of
>> r293727) a long-standing problem with noinline, where we end up
>> de facto inlining trivial functions e.g.
>> __attribute__((noinline)) int patatino(void) { return 5; }
>> because of return value propagation.
> I'm not really following why this is a problem in the first place...
> noinline doesn't mean "don't do any interprodedural optimizations". And if
> we did want it to mean that, we should do it in a more principled manner
> than scattering checks across each individual pass.

 + Hal.

Thanks for your comment, Eli.
Do you have any ideas on how to handle this more systematically? The
main reason why I special cased this for IPSCCP is that I wasn't able
to think of other passes being able to produce a similar effect (I
personally don't have a strong opinion whether we should prevent the
transformation in this case or not, maybe it's worth discussing this
on llvm-dev).


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