radv/gfx10: fix the vertex order for triangle strips emitted by a GS

My fix wasn't totally correct as pointed out by Marek.
Ported from RadeonSI.

Fixes: deafe4cc587 ("radv/gfx10: fix primitive indices orientation for NGG GS")
Signed-off-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Reviewed-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>

diff --git a/src/amd/vulkan/radv_nir_to_llvm.c b/src/amd/vulkan/radv_nir_to_llvm.c
index 8d495d2..9f44f1b 100644 (file)
--- a/src/amd/vulkan/radv_nir_to_llvm.c
+++ b/src/amd/vulkan/radv_nir_to_llvm.c
@@ -2357,7 +2357,6 @@ static void build_sendmsg_gs_alloc_req(struct radv_shader_context *ctx,
 struct ngg_prim {
        unsigned num_vertices;
        LLVMValueRef isnull;
-       LLVMValueRef swap;
        LLVMValueRef index[3];
        LLVMValueRef edgeflag[3];
 };
@@ -2367,52 +2366,19 @@ static void build_export_prim(struct radv_shader_context *ctx,
 {
        LLVMBuilderRef builder = ctx->ac.builder;
        struct ac_export_args args;
-       LLVMValueRef vertices[3];
-       LLVMValueRef odd, even;
        LLVMValueRef tmp;
 
        tmp = LLVMBuildZExt(builder, prim->isnull, ctx->ac.i32, "");
        args.out[0] = LLVMBuildShl(builder, tmp, LLVMConstInt(ctx->ac.i32, 31, false), "");
 
        for (unsigned i = 0; i < prim->num_vertices; ++i) {
-               tmp = LLVMBuildZExt(builder, prim->edgeflag[i], ctx->ac.i32, "");
-               tmp = LLVMBuildShl(builder, tmp,
-                                  LLVMConstInt(ctx->ac.i32, 9, false), "");
-               vertices[i] = LLVMBuildOr(builder, prim->index[i], tmp, "");
-       }
-
-       switch (prim->num_vertices) {
-       case 1:
-               args.out[0] = LLVMBuildOr(builder, args.out[0], vertices[0], "");
-               break;
-       case 2:
-               tmp = LLVMBuildShl(builder, vertices[1],
-                                  LLVMConstInt(ctx->ac.i32, 10, false), "");
-               tmp = LLVMBuildOr(builder, args.out[0], tmp, "");
-               args.out[0] = LLVMBuildOr(builder, tmp, vertices[0], "");
-               break;
-       case 3:
-               /* Swap vertices if needed to follow drawing order. */
-               tmp = LLVMBuildShl(builder, vertices[2],
-                                  LLVMConstInt(ctx->ac.i32, 20, false), "");
-               even = LLVMBuildOr(builder, args.out[0], tmp, "");
-               tmp = LLVMBuildShl(builder, vertices[1],
-                                  LLVMConstInt(ctx->ac.i32, 10, false), "");
-               even = LLVMBuildOr(builder, even, tmp, "");
-               even = LLVMBuildOr(builder, even, vertices[0], "");
-
-               tmp = LLVMBuildShl(builder, vertices[1],
-                                  LLVMConstInt(ctx->ac.i32, 20, false), "");
-               odd = LLVMBuildOr(builder, args.out[0], tmp, "");
-               tmp = LLVMBuildShl(builder, vertices[2],
-                                  LLVMConstInt(ctx->ac.i32, 10, false), "");
-               odd = LLVMBuildOr(builder, odd, tmp, "");
-               odd = LLVMBuildOr(builder, odd, vertices[0], "");
-
-               args.out[0] = LLVMBuildSelect(builder, prim->swap, odd, even, "");
-               break;
-       default:
-               unreachable("invalid number of vertices");
+               tmp = LLVMBuildShl(builder, prim->index[i],
+                                  LLVMConstInt(ctx->ac.i32, 10 * i, false), "");
+               args.out[0] = LLVMBuildOr(builder, args.out[0], tmp, "");
+               tmp = LLVMBuildZExt(builder, prim->edgeflag[i], ctx->ac.i32, "");
+               tmp = LLVMBuildShl(builder, tmp,
+                                  LLVMConstInt(ctx->ac.i32, 10 * i + 9, false), "");
+               args.out[0] = LLVMBuildOr(builder, args.out[0], tmp, "");
        }
 
        args.out[0] = LLVMBuildBitCast(builder, args.out[0], ctx->ac.f32, "");
@@ -3040,7 +3006,6 @@ handle_ngg_outputs_post_2(struct radv_shader_context *ctx)
 
                prim.num_vertices = num_vertices;
                prim.isnull = ctx->ac.i1false;
-               prim.swap = ctx->ac.i1false;
                memcpy(prim.index, vtxindex, sizeof(vtxindex[0]) * 3);
 
                for (unsigned i = 0; i < num_vertices; ++i) {
@@ -3338,6 +3303,7 @@ static void gfx10_ngg_gs_emit_epilogue_2(struct radv_shader_context *ctx)
        tmp = LLVMBuildICmp(builder, LLVMIntULT, tid, num_emit_threads, "");
        ac_build_ifcc(&ctx->ac, tmp, 5140);
        {
+               LLVMValueRef flags;
                struct ngg_prim prim = {};
                prim.num_vertices = verts_per_prim;
 
@@ -3348,12 +3314,8 @@ static void gfx10_ngg_gs_emit_epilogue_2(struct radv_shader_context *ctx)
                        ctx->ac.i32_0, /* primflag */
                };
                tmp = LLVMBuildGEP(builder, tmp, gep_idx, 3, "");
-               tmp = LLVMBuildLoad(builder, tmp, "");
-               prim.isnull = LLVMBuildICmp(builder, LLVMIntEQ, tmp,
-                                           LLVMConstInt(ctx->ac.i8, 0, false), "");
-               prim.swap = LLVMBuildICmp(builder, LLVMIntEQ,
-                                         LLVMBuildAnd(builder, tid, LLVMConstInt(ctx->ac.i32, 1, false), ""),
-                                         LLVMConstInt(ctx->ac.i32, 1, false), "");
+               flags = LLVMBuildLoad(builder, tmp, "");
+               prim.isnull = LLVMBuildNot(builder, LLVMBuildTrunc(builder, flags, ctx->ac.i1, ""), "");
 
                for (unsigned i = 0; i < verts_per_prim; ++i) {
                        prim.index[i] = LLVMBuildSub(builder, vertlive_scan.result_exclusive,
@@ -3361,6 +3323,24 @@ static void gfx10_ngg_gs_emit_epilogue_2(struct radv_shader_context *ctx)
                        prim.edgeflag[i] = ctx->ac.i1false;
                }
 
+               /* Geometry shaders output triangle strips, but NGG expects
+                * triangles. We need to change the vertex order for odd
+                * triangles to get correct front/back facing by swapping 2
+                * vertex indices, but we also have to keep the provoking
+                * vertex in the same place.
+                */
+               if (verts_per_prim == 3) {
+                       LLVMValueRef is_odd = LLVMBuildLShr(builder, flags, ctx->ac.i8_1, "");
+                       is_odd = LLVMBuildTrunc(builder, is_odd, ctx->ac.i1, "");
+
+                       struct ngg_prim in = prim;
+                       prim.index[0] = in.index[0];
+                       prim.index[1] = LLVMBuildSelect(builder, is_odd,
+                                                       in.index[2], in.index[1], "");
+                       prim.index[2] = LLVMBuildSelect(builder, is_odd,
+                                                       in.index[1], in.index[2], "");
+               }
+
                build_export_prim(ctx, &prim);
        }
        ac_build_endif(&ctx->ac, 5140);
@@ -3514,6 +3494,17 @@ static void gfx10_ngg_gs_emit_vertex(struct radv_shader_context *ctx,
        const LLVMValueRef iscompleteprim =
                LLVMBuildICmp(builder, LLVMIntUGE, curverts, tmp, "");
 
+       /* Since the geometry shader emits triangle strips, we need to
+        * track which primitive is odd and swap vertex indices to get
+        * the correct vertex order.
+        */
+       LLVMValueRef is_odd = ctx->ac.i1false;
+       if (stream == 0 &&
+           si_conv_gl_prim_to_vertices(ctx->shader->info.gs.output_primitive) == 3) {
+               tmp = LLVMBuildAnd(builder, curverts, ctx->ac.i32_1, "");
+               is_odd = LLVMBuildICmp(builder, LLVMIntEQ, tmp, ctx->ac.i32_1, "");
+       }
+
        tmp = LLVMBuildAdd(builder, curverts, ctx->ac.i32_1, "");
        LLVMBuildStore(builder, tmp, ctx->gs_curprim_verts[stream]);
 
@@ -3525,7 +3516,15 @@ static void gfx10_ngg_gs_emit_vertex(struct radv_shader_context *ctx,
        const LLVMValueRef primflagptr =
                LLVMBuildGEP(builder, vertexptr, gep_idx, 3, "");
 
+       /* The per-vertex primitive flag encoding:
+        *   bit 0: whether this vertex finishes a primitive
+        *   bit 1: whether the primitive is odd (if we are emitting triangle strips)
+        */
        tmp = LLVMBuildZExt(builder, iscompleteprim, ctx->ac.i8, "");
+       tmp = LLVMBuildOr(builder, tmp,
+                         LLVMBuildShl(builder,
+                                      LLVMBuildZExt(builder, is_odd, ctx->ac.i8, ""),
+                                      ctx->ac.i8_1, ""), "");
        LLVMBuildStore(builder, tmp, primflagptr);
 
        tmp = LLVMBuildLoad(builder, ctx->gs_generated_prims[stream], "");