The vector backend already implemented this optimization, but
surprisingly, we never bothered to implement it in the scalar backend.
In addition to saving two instructions, this eliminates a use of the
accumulator as an explicit source, which is unsupported in SIMD16 mode
on Gen7+, which could help us gain SIMD16 programs.
Cuts 19.23% of the instructions in dolphin/efb2ram.shader_test.
v2: Rebase on is_16bit_integer_constant -> is_uint16_constant rename.
Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Matt Turner <mattst88@gmail.com>
Kenneth Graunke
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