Mesa (staging/20.1): nir/algebraic: mark some optimizations with fsat(NaN) as inexact

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Module: Mesa
Branch: staging/20.1
Commit: 01ddfedbb84851eebc05202bdd7f42ee2e198d61
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=01ddfedbb84851eebc05202bdd7f42ee2e198d61

Author: Samuel Pitoiset <samuel.pitoiset at gmail.com>
Date:   Mon Aug 31 16:08:55 2020 +0200

nir/algebraic: mark some optimizations with fsat(NaN) as inexact

If a is Nan, fsat(NaN) is expected to be 0 and some optimizations
should be marked as inexact.

Fixes a GPU hang with Death Stranding and RADV/ACO (RADV/LLVM
isn't affected because it lowers fsat).

No fossils-db change.

Closes: https://gitlab.freedesktop.org/mesa/mesa/-/issues/3368
Cc: mesa-stable
Signed-off-by: Samuel Pitoiset <samuel.pitoiset at gmail.com>
Reviewed-by: Alyssa Rosenzweig <alyssa.rosenzweig at collabora.com>
Reviewed-by: Bas Nieuwenhuizen <bas at basnieuwenhuizen.nl>
Reviewed-by: Rhys Perry <pendingchaos02 at gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6519>
(cherry picked from commit bc123c396a99b2f6ff845792374d6a8d5de5d15e)

---

 .pick_status.json                     |  2 +-
 src/compiler/nir/nir_opt_algebraic.py | 12 +++++++++---
 2 files changed, 10 insertions(+), 4 deletions(-)

diff --git a/.pick_status.json b/.pick_status.json
index cc12395a50e..ef51187d6ad 100644
--- a/.pick_status.json
+++ b/.pick_status.json
@@ -319,7 +319,7 @@
         "description": "nir/algebraic: mark some optimizations with fsat(NaN) as inexact",
         "nominated": true,
         "nomination_type": 0,
-        "resolution": 0,
+        "resolution": 1,
         "master_sha": null,
         "because_sha": null
     },
diff --git a/src/compiler/nir/nir_opt_algebraic.py b/src/compiler/nir/nir_opt_algebraic.py
index 8f45b99060b..92bea7a4510 100644
--- a/src/compiler/nir/nir_opt_algebraic.py
+++ b/src/compiler/nir/nir_opt_algebraic.py
@@ -327,10 +327,14 @@ optimizations.extend([
    (('fne', ('fneg', a), -1.0), ('fne', 1.0, a)),
    (('feq', -1.0, ('fneg', a)), ('feq', a, 1.0)),
 
-   (('flt', ('fsat(is_used_once)', a), '#b(is_gt_0_and_lt_1)'), ('flt', a, b)),
+   # flt(fsat(a), b > 0 && b < 1) is inexact if a is NaN (fsat(NaN) is 0)
+   # because it returns True while flt(a, b) always returns False.
+   (('~flt', ('fsat(is_used_once)', a), '#b(is_gt_0_and_lt_1)'), ('flt', a, b)),
    (('flt', '#b(is_gt_0_and_lt_1)', ('fsat(is_used_once)', a)), ('flt', b, a)),
    (('fge', ('fsat(is_used_once)', a), '#b(is_gt_0_and_lt_1)'), ('fge', a, b)),
-   (('fge', '#b(is_gt_0_and_lt_1)', ('fsat(is_used_once)', a)), ('fge', b, a)),
+   # fge(b > 0 && b < 1, fsat(a)) is inexact if a is NaN (fsat(NaN) is 0)
+   # because it returns True while fge(b, a) always returns False.
+   (('~fge', '#b(is_gt_0_and_lt_1)', ('fsat(is_used_once)', a)), ('fge', b, a)),
    (('feq', ('fsat(is_used_once)', a), '#b(is_gt_0_and_lt_1)'), ('feq', a, b)),
    (('fne', ('fsat(is_used_once)', a), '#b(is_gt_0_and_lt_1)'), ('fne', a, b)),
 
@@ -1767,7 +1771,9 @@ late_optimizations = [
    (('fne', ('fsat(is_used_once)', a), '#b(is_gt_0_and_lt_1)'), ('fne', a, b)),
 
    (('fge', ('fsat(is_used_once)', a), 1.0), ('fge', a, 1.0)),
-   (('flt', ('fsat(is_used_once)', a), 1.0), ('flt', a, 1.0)),
+   # flt(fsat(a), 1.0) is inexact because it returns True if a is NaN
+   # (fsat(NaN) is 0), while flt(a, 1.0) always returns FALSE.
+   (('~flt', ('fsat(is_used_once)', a), 1.0), ('flt', a, 1.0)),
 
    (('~fge', ('fmin(is_used_once)', ('fadd(is_used_once)', a, b), ('fadd', c, d)), 0.0), ('iand', ('fge', a, ('fneg', b)), ('fge', c, ('fneg', d)))),