radeonsi: do not kill GS with memory writes

Vertex emits beyond the specified maximum number of vertices are supposed to
have no effect, which is why we used to always kill GS that reached the limit.

However, if the GS also writes to memory (SSBO, atomics, shader images), then
we must keep going and only skip the vertex emit itself.

Cc: [email protected]
Reviewed-by: Marek Olšák <[email protected]>

1 files changed, 22 insertions, 8 deletions

diff --git a/src/gallium/drivers/radeonsi/si_shader.c b/src/gallium/drivers/radeonsi/si_shader.c
index 9560baf7961..8827643caef 100644
--- a/src/gallium/drivers/radeonsi/si_shader.c
+++ b/src/gallium/drivers/radeonsi/si_shader.c
@@ -5256,6 +5256,7 @@ static void si_llvm_emit_vertex(
 	struct si_shader *shader = ctx->shader;
 	struct tgsi_shader_info *info = &shader->selector->info;
 	struct gallivm_state *gallivm = bld_base->base.gallivm;
+	struct lp_build_if_state if_state;
 	LLVMValueRef soffset = LLVMGetParam(ctx->main_fn,
 					    SI_PARAM_GS2VS_OFFSET);
 	LLVMValueRef gs_next_vertex;
@@ -5273,19 +5274,28 @@ static void si_llvm_emit_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.
+	 * vertices, skip the write: excessive vertex emissions are not
+	 * supposed to have any effect.
+	 *
+	 * If the shader has no writes to memory, kill it instead. This skips
+	 * further memory loads and may allow LLVM to skip to the end
+	 * altogether.
 	 */
 	can_emit = LLVMBuildICmp(gallivm->builder, LLVMIntULE, gs_next_vertex,
 				 lp_build_const_int32(gallivm,
 						      shader->selector->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));
 
-	lp_build_intrinsic(gallivm->builder, "llvm.AMDGPU.kill",
-			   ctx->voidt, &kill, 1, 0);
+	bool use_kill = !info->writes_memory;
+	if (use_kill) {
+		kill = lp_build_select(&bld_base->base, can_emit,
+				       lp_build_const_float(gallivm, 1.0f),
+				       lp_build_const_float(gallivm, -1.0f));
+
+		lp_build_intrinsic(gallivm->builder, "llvm.AMDGPU.kill",
+				   ctx->voidt, &kill, 1, 0);
+	} else {
+		lp_build_if(&if_state, gallivm, can_emit);
+	}
 
 	for (i = 0; i < info->num_outputs; i++) {
 		LLVMValueRef *out_ptr =
@@ -5311,6 +5321,7 @@ static void si_llvm_emit_vertex(
 					    1, 0, 1, 1, 0);
 		}
 	}
+
 	gs_next_vertex = lp_build_add(uint, gs_next_vertex,
 				      lp_build_const_int32(gallivm, 1));
 
@@ -5321,6 +5332,9 @@ static void si_llvm_emit_vertex(
 	args[1] = LLVMGetParam(ctx->main_fn, SI_PARAM_GS_WAVE_ID);
 	lp_build_intrinsic(gallivm->builder, "llvm.SI.sendmsg",
 			   ctx->voidt, args, 2, 0);
+
+	if (!use_kill)
+		lp_build_endif(&if_state);
 }
 
 /* Cut one primitive from the geometry shader */