Mesa (main): nir: Properly handle various exceptional values in frexp

[GitLab Mirror]

Module: Mesa
Branch: main
Commit: 7d0d9b9fbc231c2bd66778e0b0a62d5c514c5495
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=7d0d9b9fbc231c2bd66778e0b0a62d5c514c5495

Author: Ian Romanick <ian.d.romanick at intel.com>
Date:   Thu Oct 28 17:34:56 2021 -0700

nir: Properly handle various exceptional values in frexp

frexp_sig of ±0, ±Inf, or NaN should just return the input unmodified.

frexp_exp of ±Inf or NaN is undefined, and frexp_exp of ±0 should return
the input unmodified.  This seems to already work.

No shader-db or fossil-db changes on any Intel platform.

Reviewed-by: Caio Oliveira <caio.oliveira at intel.com>
Fixes: 23d30f4099f ("spirv,nir: lower frexp_exp/frexp_sig inside a new NIR pass")
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/13999>

---

 src/compiler/nir/nir_lower_frexp.c | 24 ++++++++++++++++++------
 1 file changed, 18 insertions(+), 6 deletions(-)

diff --git a/src/compiler/nir/nir_lower_frexp.c b/src/compiler/nir/nir_lower_frexp.c
index d4be828afdd..f270a18c4fb 100644
--- a/src/compiler/nir/nir_lower_frexp.c
+++ b/src/compiler/nir/nir_lower_frexp.c
@@ -35,7 +35,6 @@ lower_frexp_sig(nir_builder *b, nir_ssa_def *x)
    nir_ssa_def *abs_x = nir_fabs(b, x);
    nir_ssa_def *zero = nir_imm_floatN_t(b, 0, x->bit_size);
    nir_ssa_def *sign_mantissa_mask, *exponent_value;
-   nir_ssa_def *is_not_zero = nir_fneu(b, abs_x, zero);
 
    switch (x->bit_size) {
    case 16:
@@ -89,18 +88,31 @@ lower_frexp_sig(nir_builder *b, nir_ssa_def *x)
        * 32 bits using nir_unpack_64_2x32_split_y.
        */
       nir_ssa_def *upper_x = nir_unpack_64_2x32_split_y(b, x);
-      nir_ssa_def *zero32 = nir_imm_int(b, 0);
 
+      /* If x is ±0, ±Inf, or NaN, return x unmodified. */
       nir_ssa_def *new_upper =
-         nir_ior(b, nir_iand(b, upper_x, sign_mantissa_mask),
-                    nir_bcsel(b, is_not_zero, exponent_value, zero32));
+         nir_bcsel(b,
+                   nir_iand(b,
+                            nir_flt(b, zero, abs_x),
+                            nir_fisfinite(b, x)),
+                   nir_ior(b,
+                           nir_iand(b, upper_x, sign_mantissa_mask),
+                           exponent_value),
+                   upper_x);
 
       nir_ssa_def *lower_x = nir_unpack_64_2x32_split_x(b, x);
 
       return nir_pack_64_2x32_split(b, lower_x, new_upper);
    } else {
-      return nir_ior(b, nir_iand(b, x, sign_mantissa_mask),
-                        nir_bcsel(b, is_not_zero, exponent_value, zero));
+      /* If x is ±0, ±Inf, or NaN, return x unmodified. */
+      return nir_bcsel(b,
+                       nir_iand(b,
+                                nir_flt(b, zero, abs_x),
+                                nir_fisfinite(b, x)),
+                       nir_ior(b,
+                               nir_iand(b, x, sign_mantissa_mask),
+                               exponent_value),
+                       x);
    }
 }