radv: introduce RADV_DEBUG=llvm option

This option enables the LLVM compiler backend to be used
for shader compilation

Reviewed-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/5445>

docs/envvars.rst

@@ -510,6 +510,8 @@ RADV driver environment variables
 ``RADV_DEBUG``
    a comma-separated list of named flags, which do various things:
 
+   ``llvm``
+      enable LLVM compiler backend
    ``allbos``
       force all allocated buffers to be referenced in submissions
    ``allentrypoints``

src/amd/vulkan/radv_debug.h

@@ -57,6 +57,7 @@ enum {
 	RADV_DEBUG_DUMP_META_SHADERS = 0x4000000,
 	RADV_DEBUG_NO_MEMORY_CACHE   = 0x8000000,
 	RADV_DEBUG_DISCARD_TO_DEMOTE = 0x10000000,
+	RADV_DEBUG_LLVM              = 0x20000000,
 };
 
 enum {

src/amd/vulkan/radv_device.c

@@ -507,6 +507,7 @@ static const struct debug_control radv_debug_options[] = {
 	{"allentrypoints", RADV_DEBUG_ALL_ENTRYPOINTS},
 	{"metashaders", RADV_DEBUG_DUMP_META_SHADERS},
 	{"nomemorycache", RADV_DEBUG_NO_MEMORY_CACHE},
+	{"llvm", RADV_DEBUG_LLVM},
 	{NULL, 0}
 };
 
@@ -677,6 +678,10 @@ VkResult radv_CreateInstance(
 	instance->perftest_flags = parse_debug_string(getenv("RADV_PERFTEST"),
 						   radv_perftest_options);
 
+	if (instance->debug_flags & RADV_DEBUG_LLVM) {
+		instance->perftest_flags &= ~RADV_PERFTEST_ACO;
+	}
+
 	if (instance->perftest_flags & RADV_PERFTEST_ACO)
 		fprintf(stderr, "WARNING: Experimental compiler backend enabled. Here be dragons! Incorrect rendering, GPU hangs and/or resets are likely\n");