glsl: Fix software 64-bit integer to 32-bit float conversions

Graphics / Mesa 3D Graphics Library / Mesa - Francisco Jerez [riseup.net] - 10 January 2020 18:51 UTC

The current implementation was broken for any integers between 2^24 and 2^30 (it would return zero for me on ICL). The reason is that for such integers we wouldn't take the 'if (0 <= shiftCount)' early return path, however 'shiftCount + 7' would be positive, leading to a negative 'count' argument passed to __shift64RightJamming(), which would give undefined results.

This reworks the affected conversion functions to use either __shortShift64Left() or __shift64RightJamming() based on the sign of the final shift count, which should avoid the problem. In addition this should qualify as a clean-up/optimization -- This implementation of the conversion functions translates to 7 instructions less than the original on Intel hardware.

This fixes the 'KHR-GL46.shader_ballot_tests.ShaderBallotFunctionBallot' conformance tests on soft fp64 hardware with large enough subgroup size (>16).

Fixes: d5cf6e92b4f7 "glsl: Add built-in functions to do uint64_to_fp32(uint64_t)" Fixes: c9d333a6b76e "glsl: Add built-in functions to do int64_to_fp32(int64_t)" Cc: Sagar Ghuge

a30bb25a7a4 glsl: Fix software 64-bit integer to 32-bit float conversions.
src/compiler/glsl/float64.glsl | 36 ++++++++++++++----------------------
1 file changed, 14 insertions(+), 22 deletions(-)

Upstream: cgit.freedesktop.org


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