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r300: allow presubtract when both ADD sources are negative

Pavel Ondračka requested to merge ondracka/mesa:r300_presubtract_double_negate into main

Current code doesn't handle this, however it is easy to make it work by moving the negate to the presubtract source. Minor win in shader-db, mostly with Unigine shaders.

Example of such case:

 ADD temp[38].xyz, -input[1].xyz_, -temp[37].xyz_;
 DP3 temp[39].x, temp[38].xyz_, input[2].xyz_;

now becomes:

DP3 temp[39].x, (temp[37] + input[1]).-x-y-z_, input[2].xyz_;

Shader-db RV530:

total instructions in shared programs: 136382 -> 136236 (-0.11%)
instructions in affected programs: 9911 -> 9765 (-1.47%)
total temps in shared programs: 18939 -> 18942 (0.02%)
temps in affected programs: 37 -> 40 (8.11%)

Signed-off-by: Pavel Ondračka pavel.ondracka@gmail.com

Edited by Pavel Ondračka

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