radeonsi: add a debug flag that disables optimized shader variants

Reviewed-by: Edward O'Callaghan <funfunctor@folklore1984.net>
Reviewed-by: Nicolai Hähnle <nicolai.haehnle@amd.com>

src/gallium/drivers/radeon/r600_pipe_common.c

@@ -671,6 +671,7 @@ static const struct debug_named_value common_debug_options[] = {
 	{ "noasm", DBG_NO_ASM, "Don't print disassembled shaders"},
 	{ "preoptir", DBG_PREOPT_IR, "Print the LLVM IR before initial optimizations" },
 	{ "checkir", DBG_CHECK_IR, "Enable additional sanity checks on shader IR" },
+	{ "nooptvariant", DBG_NO_OPT_VARIANT, "Disable compiling optimized shader variants." },
 
 	{ "testdma", DBG_TEST_DMA, "Invoke SDMA tests and exit." },
 

src/gallium/drivers/radeon/r600_pipe_common.h

@@ -79,6 +79,7 @@
 #define DBG_NO_ASM		(1 << 14)
 #define DBG_PREOPT_IR		(1 << 15)
 #define DBG_CHECK_IR		(1 << 16)
+#define DBG_NO_OPT_VARIANT	(1 << 17)
 /* gaps */
 #define DBG_TEST_DMA		(1 << 20)
 /* Bits 21-31 are reserved for the r600g driver. */

src/gallium/drivers/radeonsi/si_state_shaders.c

@@ -1121,6 +1121,11 @@ static int si_shader_select_with_key(struct si_screen *sscreen,
 	struct si_shader_selector *sel = state->cso;
 	struct si_shader *current = state->current;
 	struct si_shader *iter, *shader = NULL;
+
+	if (unlikely(sscreen->b.chip_class & DBG_NO_OPT_VARIANT)) {
+		memset(&key->opt, 0, sizeof(key->opt));
+	}
+
 again:
 	/* Check if we don't need to change anything.
 	 * This path is also used for most shaders that don't need multiple