[Mesa-dev] [Bug 106246] radv: VK_PIPELINE_CREATE_DISABLE_OPTIMIZATION_BIT and bringing down initial pipeline compile times

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=106246

--- Comment #7 from Timothy Arceri <t_arceri at yahoo.com.au> ---
(In reply to Timothy Arceri from comment #6)
> (In reply to Timothy Arceri from comment #4)
> > (In reply to Nicolai Hähnle from comment #3)
> > > As long as scratch buffer support is robust, removing LLVM IR optimization
> > > passes is probably not a problem, though you really do want mem2reg and I
> > > don't think we spend much time in the others (at least radeonsi didn't, last
> > > time I checked).
> > > 
> > > Using the -O0 settings for the codegen backend is a lot riskier. Our compute
> > > folks have done some work fixing bugs there, but I really wouldn't recommend
> > > it.
> > 
> > Yeah I've done some experimenting with the Blacksmith demo. I'm not sure we
> > can get much benefit implementing
> > VK_PIPELINE_CREATE_DISABLE_OPTIMIZATION_BIT with the current state of
> > things. 
> > 
> > Default:
> > Sum of shader compile times: 325933 ms
> > 
> > With only LLVM DCE opt (compilation fails without this):
> > Sum of shader compile times: 326451 ms
> > 
> > No NIR linking plus single pass over NIR opts (compilation fails without
> > this):
> > Sum of shader compile times: 294788 ms
> 
> I've done some playing around with the LLVM cogegen opt levels:
> 
> LLVMCodeGenLevelNone + LLVMAddEarlyCSEMemSSAPass (compilation fails without
> this):
> Sum of shader compile times: 211403 ms
> However there are all sorts of rendering issues when running the demo.
> 
> No NIR linking plus single pass over NIR opts (compilation fails without
> this),
> LLVMCodeGenLevelNone + LLVMAddEarlyCSEMemSSAPass(compilation fails without
> this):
> Sum of shader compile times: 179775 ms
> With this the demo doesn't actually display the graphics it just shows a
> flickering Unity logo throughout the run.

Ok so it seems this speed up (and the display issues that go with it) and due
to switching from the GreedyRegisterAllocator to the FastRegisterAllocator.

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