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src/intel/compiler/brw/brw_nir_workarounds.py

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+# Copyright © 2016 Intel Corporation
+# SPDX-License-Identifier: MIT
+
+# Prior to Kaby Lake, The SIN and COS instructions on Intel hardware can
+# produce values slightly outside of the [-1.0, 1.0] range for a small set of
+# values.  Obviously, this can break everyone's expectations about trig
+# functions.  This appears to be fixed in Kaby Lake.
+#
+# According to an internal presentation, the COS instruction can produce
+# a value up to 1.000027 for inputs in the range (0.08296, 0.09888).  One
+# suggested workaround is to multiply by 0.99997, scaling down the
+# amplitude slightly.  Apparently this also minimizes the error function,
+# reducing the maximum error from 0.00006 to about 0.00003.
+
+import argparse
+import sys
+from math import pi
+
+TRIG_WORKAROUNDS = [
+    (('fsin', 'x(is_not_const)'), ('fmul', ('fsin', 'x'), 0.99997)),
+    (('fcos', 'x(is_not_const)'), ('fmul', ('fcos', 'x'), 0.99997)),
+]
+
+LIMIT_TRIG_INPUT_RANGE_WORKAROUND = [
+    (('fsin', 'x(is_not_const)'), ('fsin', ('fmod', 'x', 2.0 * pi))),
+    (('fcos', 'x(is_not_const)'), ('fcos', ('fmod', 'x', 2.0 * pi))),
+]
+
+SQRT_WORKAROUND = [
+    (('fsqrt', 'x(is_not_const)'), ('fsqrt', ('fmax', 'x', 1e-12))),
+]
+
+def main():
+    parser = argparse.ArgumentParser()
+    parser.add_argument('-p', '--import-path', required=True)
+    args = parser.parse_args()
+    sys.path.insert(0, args.import_path)
+    run()
+
+
+def run():
+    import nir_algebraic  # pylint: disable=import-error
+
+    print('#include "brw_nir.h"')
+    print(nir_algebraic.AlgebraicPass("brw_nir_apply_trig_workarounds",
+                                      TRIG_WORKAROUNDS).render())
+    print(nir_algebraic.AlgebraicPass("brw_nir_limit_trig_input_range_workaround",
+                                      LIMIT_TRIG_INPUT_RANGE_WORKAROUND).render())
+    print(nir_algebraic.AlgebraicPass("brw_nir_apply_sqrt_workarounds",
+                                      SQRT_WORKAROUND).render())
+
+
+if __name__ == '__main__':
+    main()