nir/algebraic: add fexp2(fmul(flog2(a), 0.5) -> fsqrt(a) optimization

Helps some Wolfenstein II and Wolfenstein Youngblood shaders.

pipeline-db (VEGA10/ACO):
Totals from affected shaders:
SGPRS: 17904 -> 17904 (0.00 %)
VGPRS: 14492 -> 14492 (0.00 %)
Spilled SGPRs: 20 -> 20 (0.00 %)
Spilled VGPRs: 0 -> 0 (0.00 %)
Code Size: 1753152 -> 1749708 (-0.20 %) bytes
Max Waves: 2581 -> 2581 (0.00 %)

pipeline-db (VEGA10/LLVM):
Totals from affected shaders:
SGPRS: 26656 -> 26656 (0.00 %)
VGPRS: 23780 -> 23780 (0.00 %)
Spilled SGPRs: 2112 -> 2112 (0.00 %)
Spilled VGPRs: 0 -> 0 (0.00 %)
Code Size: 2552712 -> 2549236 (-0.14 %) bytes
Max Waves: 3359 -> 3359 (0.00 %)

Signed-off-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Reviewed-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Tested-by: Marge Bot <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4353>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4353>

diff --git a/src/compiler/nir/nir_opt_algebraic.py b/src/compiler/nir/nir_opt_algebraic.py
index 3302cd8d9e1ec9d9d86cb2cb0b434f295e581f7d..1625d6703e28aea01b62999ab04f05a965f1e6f4 100644 (file)
--- a/src/compiler/nir/nir_opt_algebraic.py
+++ b/src/compiler/nir/nir_opt_algebraic.py
@@ -787,6 +787,7 @@ optimizations.extend([
    (('~fexp2', ('fmul', ('flog2', a), b)), ('fpow', a, b), '!options->lower_fpow'), # 2^(lg2(a)*b) = a^b
    (('~fexp2', ('fadd', ('fmul', ('flog2', a), b), ('fmul', ('flog2', c), d))),
     ('~fmul', ('fpow', a, b), ('fpow', c, d)), '!options->lower_fpow'), # 2^(lg2(a) * b + lg2(c) + d) = a^b * c^d
+   (('~fexp2', ('fmul', ('flog2', a), 0.5)), ('fsqrt', a)),
    (('~fexp2', ('fmul', ('flog2', a), 2.0)), ('fmul', a, a)),
    (('~fexp2', ('fmul', ('flog2', a), 4.0)), ('fmul', ('fmul', a, a), ('fmul', a, a))),
    (('~fpow', a, 1.0), a),