radeonsi: enable ACO by default for pre-GFX10 GPUs

User can set AMD_DEBUG=usellvm to switch back to LLVM.

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/32742>

src/gallium/drivers/radeonsi/si_pipe.c

@@ -66,6 +66,7 @@ static const struct debug_named_value radeonsi_debug_options[] = {
    {"mono", DBG(MONOLITHIC_SHADERS), "Use old-style monolithic shaders compiled on demand"},
    {"nooptvariant", DBG(NO_OPT_VARIANT), "Disable compiling optimized shader variants."},
    {"useaco", DBG(USE_ACO), "Use ACO as shader compiler when possible"},
+   {"usellvm", DBG(USE_LLVM), "Use LLVM as shader compiler when possible"},
 
    /* Information logging options: */
    {"info", DBG(INFO), "Print driver information"},
@@ -1189,19 +1190,23 @@ static struct pipe_screen *radeonsi_screen_create_impl(struct radeon_winsys *ws,
    if (sscreen->debug_flags & DBG(SHADOW_REGS))
       sscreen->info.register_shadowing_required = true;
 
+   bool support_aco = aco_is_gpu_supported(&sscreen->info);
+
 #if AMD_LLVM_AVAILABLE
    /* For GFX11.5, LLVM < 19 is missing a workaround that can cause GPU hangs. ACO is the only
     * alternative that has the workaround and is always available.
     */
    if (sscreen->info.gfx_level == GFX11_5 && LLVM_VERSION_MAJOR < 19)
       sscreen->use_aco = true;
-   else
+   else if (sscreen->info.gfx_level >= GFX10)
       sscreen->use_aco = (sscreen->debug_flags & DBG(USE_ACO));
+   else
+      sscreen->use_aco = support_aco && sscreen->info.has_image_opcodes &&
+                         !(sscreen->debug_flags & DBG(USE_LLVM));
 #else
    sscreen->use_aco = true;
 #endif
 
-   bool support_aco = aco_is_gpu_supported(&sscreen->info);
    if (sscreen->use_aco && !support_aco) {
       fprintf(stderr, "radeonsi: ACO does not support this chip yet\n");
       FREE(sscreen);

src/gallium/drivers/radeonsi/si_pipe.h

@@ -239,6 +239,7 @@ enum
    DBG_TMZ,
    DBG_SQTT,
    DBG_USE_ACO,
+   DBG_USE_LLVM,
 
    DBG_COUNT
 };