nir: Implement CSE on intrinsics that can be eliminated and reordered

Graphics / Mesa 3D Graphics Library / Mesa - Kenneth Graunke [whitecape.org] - 23 January 2015 16:53 UTC

Matt and I noticed that one of the shaders hurt by INTEL_USE_NIR=1 had load_input and load_uniform intrinsics repeated several times, with the same parameters, but each one generating a distinct SSA value. This made ALU operations on those values appear distinct as well.

Generating distinct SSA values is silly - these are read only variables. CSE'ing them makes everything use a single SSA value, which then allows other operations to be CSE'd away as well.

Generalizing a bit, it seems like we should be able to safely CSE any intrinsics that can be eliminated and reordered. I didn't implement support for variables for the time being.

v2: Assert that info->num_variables == 0 (requested by Jason).

total NIR instructions in shared programs: 2435936 -> 2023511 (-16.93%) NIR instructions in affected programs: 2413496 -> 2001071 (-17.09%) helped: 16872

total i965 instructions in shared programs: 6028987 -> 6008427 (-0.34%) i965 instructions in affected programs: 640654 -> 620094 (-3.21%) helped: 2071 HURT: 585 GAINED: 14 LOST: 25

978b0a9 nir: Implement CSE on intrinsics that can be eliminated and reordered.
src/glsl/nir/nir_opt_cse.c | 40 ++++++++++++++++++++++++++++++++++++++--
1 file changed, 38 insertions(+), 2 deletions(-)

Upstream: cgit.freedesktop.org

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