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i965/fs: Add a comment explaining how register coalescing works.

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Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
This commit is contained in:
Matt Turner
2013-12-10 16:05:19 -08:00
parent 2dfb067139
commit 9bb4d71fd2
1 changed files with 12 additions and 0 deletions
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src/mesa/drivers/dri/i965/brw_fs.cpp
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@@ -2256,6 +2256,18 @@ fs_visitor::dead_code_eliminate_local()
* Implements register coalescing: Checks if the two registers involved in a * Implements register coalescing: Checks if the two registers involved in a
* raw move don't interfere, in which case they can both be stored in the same * raw move don't interfere, in which case they can both be stored in the same
* place and the MOV removed. * place and the MOV removed.
*
* To do this, all uses of the source of the MOV in the shader are replaced
* with the destination of the MOV. For example:
*
* add vgrf3:F, vgrf1:F, vgrf2:F
* mov vgrf4:F, vgrf3:F
* mul vgrf5:F, vgrf5:F, vgrf4:F
*
* becomes
*
* add vgrf4:F, vgrf1:F, vgrf2:F
* mul vgrf5:F, vgrf5:F, vgrf4:F
*/ */
bool bool
fs_visitor::register_coalesce() fs_visitor::register_coalesce()