[Bug 94900] HD6950 GPU lockup loop with various steam games (octodad[always], saints row 4[always], dead island[always], grid autosport[sometimes])

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=94900

--- Comment #19 from iive at yahoo.com ---
Created attachment 125130
  --> https://bugs.freedesktop.org/attachment.cgi?id=125130&action=edit
Octrodad crashing pixel shader - TGSI, disassembly, sbdump of IR code and crash
backtrace

I've discovered few more things.

1. When retracing with mesa3d debug enabled, the shader backend internal
checker is run and it does detect errors (and crashes at failed assert). It
seems to error out at shader 70 (a draw command before the one that hangs).
I've attached a log that includes the output of `sbdump` too.

2. `R600_DEBUG=sbsafemath` could also be used to workaround the above crash and
the original lockup. (Please test if this works with the other titles too.)

Looking at the source, the 'safe math' option skips few optimization. The one
that seems to cause problem is the call to `fold_assoc()` in
`expr_handler::fold_alu_op2()` somewhere around `sb_expr.cpp:740`.

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