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glsl: Find the "closest" signature when there are multiple matches.
Previously, ir_function::matching_signature had a fatal bug: if a
function had more than one non-exact match, it would simply return NULL.
This occured, for example, when looking for max(uvec3, uvec3):
- max(vec3, vec3) -> score 1 (found first)
- max(ivec3, ivec3) -> score 1 (found second...used to return NULL here)
- max(uvec3, uvec3) -> score 0 (exact match...the right answer)
This did not occur for max(ivec3, ivec3) since the second match found
was an exact match.
The new behavior is to return a match with the lowest score. If there
is an exact match, that will be returned. Otherwise, a match with the
least number of implicit conversions is chosen.
Fixes piglit tests max-uvec3.vert and glsl-inexact-overloads.shader_test.
NOTE: This is a candidate for the 7.10 and 7.11 branches.
Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Eric Anholt <eric@anholt.net>