[Mesa-dev] [PATCH] radeonsi: Prevent geometry shader from emitting too many vertices

[Michel Dänzer]

From: Michel Daenzer <michel.daenzer at amd.com>

Signed-off-by: Michel Dänzer <michel.daenzer at amd.com>
---
 src/gallium/drivers/radeonsi/si_shader.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/src/gallium/drivers/radeonsi/si_shader.c b/src/gallium/drivers/radeonsi/si_shader.c
index 54270cd..b22db0b 100644
--- a/src/gallium/drivers/radeonsi/si_shader.c
+++ b/src/gallium/drivers/radeonsi/si_shader.c
@@ -1905,6 +1905,7 @@ static void si_llvm_emit_vertex(
 	LLVMValueRef soffset = LLVMGetParam(si_shader_ctx->radeon_bld.main_fn,
 					    SI_PARAM_GS2VS_OFFSET);
 	LLVMValueRef gs_next_vertex;
+	LLVMValueRef can_emit, kill;
 	LLVMValueRef t_list_ptr;
 	LLVMValueRef t_list;
 	LLVMValueRef args[2];
@@ -1934,6 +1935,21 @@ static void si_llvm_emit_vertex(
 
 	/* Write vertex attribute values to GSVS ring */
 	gs_next_vertex = LLVMBuildLoad(gallivm->builder, si_shader_ctx->gs_next_vertex, "");
+
+	/* If this thread has already emitted the declared maximum number of
+	 * vertices, kill it: excessive vertex emissions are not supposed to
+	 * have any effect, and GS threads have no externally observable
+	 * effects other than emitting vertices.
+	 */
+	can_emit = LLVMBuildICmp(gallivm->builder, LLVMIntULE, gs_next_vertex,
+				 lp_build_const_int32(gallivm,
+						      shader->gs_max_out_vertices), "");
+	kill = lp_build_select(&bld_base->base, can_emit,
+			       lp_build_const_float(gallivm, 1.0f),
+			       lp_build_const_float(gallivm, -1.0f));
+	build_intrinsic(gallivm->builder, "llvm.AMDGPU.kill",
+			LLVMVoidTypeInContext(gallivm->context), &kill, 1, 0);
+
 	for (i = 0; i < shader->noutput; i++) {
 		LLVMValueRef *out_ptr =
 			si_shader_ctx->radeon_bld.soa.outputs[shader->output[i].index];
-- 
1.9.0