mesa: add MESA_NO_MINMAX_CACHE environment variable

When set to a truish value, this globally disables the minmax cache for all
buffer objects.

No #ifdef DEBUG guards because this option can be interesting for
benchmarking.

Reviewed-by: Marek Olšák <marek.olsak@amd.com>

docs/envvars.html

@@ -96,6 +96,7 @@ glGetString(GL_SHADING_LANGUAGE_VERSION). Valid values are integers, such as
 "130".  Mesa will not really implement all the features of the given language version
 if it's higher than what's normally reported. (for developers only)
 <li>MESA_GLSL - <a href="shading.html#envvars">shading language compiler options</a>
+<li>MESA_NO_MINMAX_CACHE - when set, the minmax index cache is globally disabled.
 </ul>
 
 

src/mesa/main/bufferobj.c

@@ -32,6 +32,7 @@
 
 #include <stdbool.h>
 #include <inttypes.h>  /* for PRId64 macro */
+#include "util/debug.h"
 #include "glheader.h"
 #include "enums.h"
 #include "hash.h"
@@ -520,6 +521,24 @@ _mesa_reference_buffer_object_(struct gl_context *ctx,
 }
 
 
+/**
+ * Get the value of MESA_NO_MINMAX_CACHE.
+ */
+static bool
+get_no_minmax_cache()
+{
+   static bool read = false;
+   static bool disable = false;
+
+   if (!read) {
+      disable = env_var_as_boolean("MESA_NO_MINMAX_CACHE", false);
+      read = true;
+   }
+
+   return disable;
+}
+
+
 /**
  * Initialize a buffer object to default values.
  */
@@ -533,6 +552,9 @@ _mesa_initialize_buffer_object(struct gl_context *ctx,
    obj->RefCount = 1;
    obj->Name = name;
    obj->Usage = GL_STATIC_DRAW_ARB;
+
+   if (get_no_minmax_cache())
+      obj->UsageHistory |= USAGE_DISABLE_MINMAX_CACHE;
 }