[Mesa-dev] radeonsi: LLVM r187139 broke some piglit tests

[Michel Dänzer]

On Don, 2013-08-15 at 09:16 -0700, Tom Stellard wrote:
> On Thu, Aug 15, 2013 at 08:22:39AM -0700, Tom Stellard wrote:
> > On Thu, Aug 15, 2013 at 11:55:36AM +0200, Michel Dänzer wrote:
> > > On Fre, 2013-08-02 at 17:58 +0200, Michel Dänzer wrote:
> > > > On Mit, 2013-07-31 at 08:42 -0700, Tom Stellard wrote:
> > > > > On Wed, Jul 31, 2013 at 01:04:01PM +0200, Michel Dänzer wrote:
> > > > > > 
> > > > > > LLVM revision 187139 ('Allocate local registers in order for optimal
> > > > > > coloring.') broke some derivative related piglit tests with the radeonsi
> > > > > > driver. 
> > > > > > 
> > > > > > I'm attaching a diff between the bad and good generated code (as printed
> > > > > > with RADEON_DUMP_SHADERS=1) for the glsl-derivs test. The only
> > > > > > difference I can see is in which registers are used in which order.
> > > > > > 
> > > > > > I wonder if we might be missing S_WAITCNT after DS_READ/WRITE
> > > > > > instructions in some cases, but I haven't spotted any candidates for
> > > > > > that in the bad code which aren't there in the good code as well. Can
> > > > > > anyone else spot something I've missed?
> > > > > 
> > > > > Shouldn't we be using the S_BARRIER instruction to keep the threads in sync?
> > > > 
> > > > Doesn't seem to help unfortunately, but thanks for the good suggestion.
> > > 
> > > I found one thing going wrong: DS_WRITE_B32 ends up using a VGPR
> > > register number instead of the $gds operand for encoding the GDS field
> > > (the asm output from llc even shows the VGPR name). If the VGPR number
> > > happens to be odd (i.e. to have the least significant bit set), the
> > > shader ends up writing to GDS instead of LDS.
> > >
> > 
> > Ouch, that's a pretty bad bug.
> > 
> > > But I have no idea why this is happening, or how to fix it. :(
> > > 
> > > 
> > 
> > I can take a look at it.
> 
> The attached patch should fix the problem, can you test?

Thanks for finding my silly mistake.

However, I'd like to preserve the ability to use these instructions for
GDS access, and the logic in SIInsertWaits::getHwCounts() only really
makes sense for SMRD anyway.

How about this patch instead? It fixes the piglit regressions that
prompted me to start this thread.


-- 
Earthling Michel Dänzer           |                   http://www.amd.com
Libre software enthusiast         |          Debian, X and DRI developer
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