[Mesa-dev] [PATCH 2/2] radv: copy indirect lowering settings from radeonsi

[Timothy Arceri]

It looks the original indirect mask was probably copied from
ANV.

Sascha Willems demo results:

tessellation ~4000 -> ~4200 fps

V2: continue lowering local indirect due to llvm deficiencies.

Cc: Alex Smith <asmith at feralinteractive.com>
---
 src/amd/vulkan/radv_shader.c | 27 ++++++++++++++++++++++++++-
 1 file changed, 26 insertions(+), 1 deletion(-)

diff --git a/src/amd/vulkan/radv_shader.c b/src/amd/vulkan/radv_shader.c
index 055787a705..faba0c50e9 100644
--- a/src/amd/vulkan/radv_shader.c
+++ b/src/amd/vulkan/radv_shader.c
@@ -238,22 +238,47 @@ radv_shader_compile_to_nir(struct radv_device *device,
 		NIR_PASS_V(nir, nir_lower_constant_initializers, ~0);
 		NIR_PASS_V(nir, nir_lower_system_values);
 		NIR_PASS_V(nir, nir_lower_clip_cull_distance_arrays);
 	}
 
 	/* Vulkan uses the separate-shader linking model */
 	nir->info.separate_shader = true;
 
 	nir_shader_gather_info(nir, entry_point->impl);
 
+	/* While it would be nice not to have this flag, we are constrained
+	 * by the reality that LLVM 5.0 doesn't have working VGPR indexing
+	 * on GFX9.
+	 */
+	bool llvm_has_working_vgpr_indexing =
+		device->physical_device->rad_info.chip_class <= VI;
+
+	/* TODO: Indirect indexing of GS inputs is unimplemented.
+	 *
+	 * TCS and TES load inputs directly from LDS or offchip memory, so
+	 * indirect indexing is trivial.
+	 */
 	nir_variable_mode indirect_mask = 0;
-	indirect_mask |= nir_var_shader_in;
+	if (nir->stage == MESA_SHADER_GEOMETRY ||
+	    (nir->stage != MESA_SHADER_TESS_CTRL &&
+	     nir->stage != MESA_SHADER_TESS_EVAL &&
+	     !llvm_has_working_vgpr_indexing)) {
+		indirect_mask |= nir_var_shader_in;
+	}
+
+	/* TODO: We shouldn't need to do this, however LLVM isn't currently
+	 * smart enough to handle indirects without causing excess spilling
+	 * causing the gpu to hang.
+	 *
+	 * See the following thread for more details of the problem:
+	 * https://lists.freedesktop.org/archives/mesa-dev/2017-July/162106.html
+	 */
 	indirect_mask |= nir_var_local;
 
 	nir_lower_indirect_derefs(nir, indirect_mask);
 
 	static const nir_lower_tex_options tex_options = {
 	  .lower_txp = ~0,
 	};
 
 	nir_lower_tex(nir, &tex_options);
 
-- 
2.13.6