nir: drop NaN fixup for atan

this existed due to the min/max, per the comment. now that we don't do min/max,
the whole routine is NaN correct so the fixup is pointless.

Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Suggested-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Georg Lehmann <dadschoorse@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/30934>

src/compiler/nir/nir_builtin_builder.c

@@ -208,28 +208,7 @@ nir_atan(nir_builder *b, nir_def *y_over_x)
    nir_def *tmp = nir_ffma(b, nir_fabs(b, u), res, bias);
 
    /* sign fixup */
-   nir_def *result = nir_copysign(b, tmp, y_over_x);
-
-   /* The fmin and fmax above will filter out NaN values.  This leads to
-    * non-NaN results for NaN inputs.  Work around this by doing
-    *
-    *    !isnan(y_over_x) ? ... : y_over_x;
-    */
-   if (b->exact ||
-       nir_is_float_control_signed_zero_inf_nan_preserve(b->fp_fast_math, bit_size)) {
-      const bool exact = b->exact;
-
-      b->exact = true;
-      nir_def *is_not_nan = nir_feq(b, y_over_x, y_over_x);
-      b->exact = exact;
-
-      /* The extra 1.0*y_over_x ensures that subnormal results are flushed to
-       * zero.
-       */
-      result = nir_bcsel(b, is_not_nan, result, nir_fmul_imm(b, y_over_x, 1.0));
-   }
-
-   return result;
+   return nir_copysign(b, tmp, y_over_x);
 }
 
 nir_def *