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>

diff --git a/src/glsl/ir_function.cpp b/src/glsl/ir_function.cpp
index caee929..ef8d4fc 100644 (file)
--- a/src/glsl/ir_function.cpp
+++ b/src/glsl/ir_function.cpp
@@ -165,6 +165,7 @@ ir_function_signature *
 ir_function::matching_signature(const exec_list *actual_parameters)
 {
    ir_function_signature *match = NULL;
+   int matched_score;
 
    foreach_iter(exec_list_iterator, iter, signatures) {
       ir_function_signature *const sig =
@@ -173,14 +174,14 @@ ir_function::matching_signature(const exec_list *actual_parameters)
       const int score = parameter_lists_match(& sig->parameters,
                                              actual_parameters);
 
+      /* If we found an exact match, simply return it */
       if (score == 0)
         return sig;
 
-      if (score > 0) {
-        if (match != NULL)
-           return NULL;
-
+      /* If we found a match with fewer conversions, use that instead */
+      if (score > 0 && (match == NULL || score < matched_score)) {
         match = sig;
+        matched_score = score;
       }
    }