[Bug 31830] [bisected] broken shadows in Unigine Sanctuary and Lightsmark

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=31830

--- Comment #19 from Marek Olšák <maraeo at gmail.com> 2011-01-28 10:56:20 PST ---
I think I know the reason why it's slow with the rename_regs pass.

The statistics of the most complex shader are:

~~~~~~~~ FRAGMENT PROGRAM ~~~~~~~
~ 108 Instructions
~  71 Vector Instructions (RGB)
~  35 Scalar Instructions (Alpha)
~   0 Flow Control Instructions
~  36 Texture Instructions
~   2 Presub Operations
~  36 Temporary Registers
~~~~~~~~~~~~~~ END ~~~~~~~~~~~~~~

If you disable rename_regs, you will get:

~~~~~~~~ FRAGMENT PROGRAM ~~~~~~~
~ 143 Instructions
~  71 Vector Instructions (RGB)
~  35 Scalar Instructions (Alpha)
~   0 Flow Control Instructions
~  36 Texture Instructions
~   2 Presub Operations
~   4 Temporary Registers
~~~~~~~~~~~~~~ END ~~~~~~~~~~~~~~

Wow, 4 temps! It definitely appears to be a register allocator issue. Even
though the rename_regs pass has helped with instruction scheduling a lot, it
made regalloc perform much worse.

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