nir/lower_mediump: don't use fp16 for constants if the result is denormal

Image stores are not required to preserve denorms.

Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Reviewed-by: Emma Anholt <emma@anholt.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/21622>

diff --git a/src/compiler/nir/nir_lower_mediump.c b/src/compiler/nir/nir_lower_mediump.c
index c1baabf..2e7a40d 100644 (file)
--- a/src/compiler/nir/nir_lower_mediump.c
+++ b/src/compiler/nir/nir_lower_mediump.c
@@ -749,7 +749,9 @@ static bool
 const_is_f16(nir_ssa_scalar scalar)
 {
    double value = nir_ssa_scalar_as_float(scalar);
-   return value == _mesa_half_to_float(_mesa_float_to_half(value));
+   uint16_t fp16_val = _mesa_float_to_half(value);
+   bool is_denorm = (fp16_val & 0x7fff) != 0 && (fp16_val & 0x7fff) <= 0x3ff;
+   return value == _mesa_half_to_float(fp16_val) && !is_denorm;
 }
 
 static bool