Decode and translate v_add/mul/fma/min/max/ldexp_f64, v_trunc/ceil/floor/
rndne/fract_f64, v_frexp_mant/exp_i32_f64 and the f64 <-> f32/i32/u32
conversions. f64 values stay as their raw bits (U64) in the IR and are
bitcast to double in SPIR-V, which needs the Float64 capability: the
device enables shaderFloat64 when it also preserves signed zero, inf and
NaN for 64-bit floats, and the shader declares SignedZeroInfNanPreserve 64.
Semantics measured on RDNA2 hardware (8209 inputs per op): literals are
the high dword, the 1/(2*pi) inline constant is the exact double,
omod is ignored, clamp maps NaN to +0, min/max quiet a
signaling NaN and drop a quiet one, NaN results are quiet, and the
integer conversions saturate with NaN -> 0. Truncation, rounding and
ldexp are done on the bits so they do not depend on the driver: lavapipe
returned wrong results for f64 RoundEven and Trunc, and GLSL Ldexp is
undefined past +-1024. Fma is NoContraction so RADV keeps it fused.
Co-Authored-By: Claude <noreply@anthropic.com>
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