diff options
| author | Ian Romanick <[email protected]> | 2019-11-27 13:22:38 -0800 |
|---|---|---|
| committer | Marge Bot <[email protected]> | 2020-01-23 00:18:57 +0000 |
| commit | d3d970166cad7d834811fd1f8bcd6c53db706bce (patch) | |
| tree | 94a59c0c6c499fa8c534a970b3f92034e983fb4e | |
| parent | dcadbd2dd222ecaa4f14bdadf90587bda83deba7 (diff) | |
nir/algebraic: Add lowering for 64-bit iadd_sat and isub_sat
v2: Rearranged and expand the comment about the optimizations applied to
the lowering. Suggested by Caio.
Reviewed-by: Caio Marcelo de Oliveira Filho <[email protected]>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/767>
| -rw-r--r-- | src/compiler/nir/nir_opt_algebraic.py | 50 |
1 files changed, 50 insertions, 0 deletions
diff --git a/src/compiler/nir/nir_opt_algebraic.py b/src/compiler/nir/nir_opt_algebraic.py index ecc8779198b..c52522379c6 100644 --- a/src/compiler/nir/nir_opt_algebraic.py +++ b/src/compiler/nir/nir_opt_algebraic.py @@ -1013,6 +1013,56 @@ optimizations.extend([ (('usub_sat', a, b), ('bcsel', ('ult', a, b), 0, ('isub', a, b)), 'options->lower_add_sat'), (('usub_sat@64', a, b), ('bcsel', ('ult', a, b), 0, ('isub', a, b)), 'options->lower_usub_sat64 || (options->lower_int64_options & nir_lower_iadd64) != 0'), + # int64_t sum = a + b; + # + # if (a < 0 && b < 0 && a < sum) + # sum = INT64_MIN; + # } else if (a >= 0 && b >= 0 && sum < a) + # sum = INT64_MAX; + # } + # + # A couple optimizations are applied. + # + # 1. a < sum => sum >= 0. This replacement works because it is known that + # a < 0 and b < 0, so sum should also be < 0 unless there was + # underflow. + # + # 2. sum < a => sum < 0. This replacement works because it is known that + # a >= 0 and b >= 0, so sum should also be >= 0 unless there was + # overflow. + # + # 3. Invert the second if-condition and swap the order of parameters for + # the bcsel. !(a >= 0 && b >= 0 && sum < 0) becomes !(a >= 0) || !(b >= + # 0) || !(sum < 0), and that becomes (a < 0) || (b < 0) || (sum >= 0) + # + # On Intel Gen11, this saves ~11 instructions. + (('iadd_sat@64', a, b), ('bcsel', + ('iand', ('iand', ('ilt', a, 0), ('ilt', b, 0)), ('ige', ('iadd', a, b), 0)), + 0x8000000000000000, + ('bcsel', + ('ior', ('ior', ('ilt', a, 0), ('ilt', b, 0)), ('ige', ('iadd', a, b), 0)), + ('iadd', a, b), + 0x7fffffffffffffff)), + '(options->lower_int64_options & nir_lower_iadd64) != 0'), + + # int64_t sum = a - b; + # + # if (a < 0 && b >= 0 && a < sum) + # sum = INT64_MIN; + # } else if (a >= 0 && b < 0 && a >= sum) + # sum = INT64_MAX; + # } + # + # Optimizations similar to the iadd_sat case are applied here. + (('isub_sat@64', a, b), ('bcsel', + ('iand', ('iand', ('ilt', a, 0), ('ige', b, 0)), ('ige', ('isub', a, b), 0)), + 0x8000000000000000, + ('bcsel', + ('ior', ('ior', ('ilt', a, 0), ('ige', b, 0)), ('ige', ('isub', a, b), 0)), + ('isub', a, b), + 0x7fffffffffffffff)), + '(options->lower_int64_options & nir_lower_iadd64) != 0'), + # Alternative lowering that doesn't rely on bfi. (('bitfield_insert', 'base', 'insert', 'offset', 'bits'), ('bcsel', ('ult', 31, 'bits'), |