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1 /*
2  Copyright (C) Intel Corp.  2006.  All Rights Reserved.
3  Intel funded Tungsten Graphics to
4  develop this 3D driver.
5 
6  Permission is hereby granted, free of charge, to any person obtaining
7  a copy of this software and associated documentation files (the
8  "Software"), to deal in the Software without restriction, including
9  without limitation the rights to use, copy, modify, merge, publish,
10  distribute, sublicense, and/or sell copies of the Software, and to
11  permit persons to whom the Software is furnished to do so, subject to
12  the following conditions:
13 
14  The above copyright notice and this permission notice (including the
15  next paragraph) shall be included in all copies or substantial
16  portions of the Software.
17 
18  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
19  EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
20  MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
21  IN NO EVENT SHALL THE COPYRIGHT OWNER(S) AND/OR ITS SUPPLIERS BE
22  LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
23  OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
24  WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
25 
26  **********************************************************************/
27  /*
28   * Authors:
29   *   Keith Whitwell <keithw@vmware.com>
30   */
31 
32 
33 #include "main/macros.h"
34 #include "main/enums.h"
35 
36 #include "program/program.h"
37 #include "intel_batchbuffer.h"
38 
39 #include "brw_defines.h"
40 #include "brw_context.h"
41 #include "brw_eu.h"
42 #include "brw_ff_gs.h"
43 
44 /**
45  * Allocate registers for GS.
46  *
47  * If sol_program is true, then:
48  *
49  * - The thread will be spawned with the "SVBI Payload Enable" bit set, so GRF
50  *   1 needs to be set aside to hold the streamed vertex buffer indices.
51  *
52  * - The thread will need to use the destination_indices register.
53  */
brw_ff_gs_alloc_regs(struct brw_ff_gs_compile * c,GLuint nr_verts,bool sol_program)54 static void brw_ff_gs_alloc_regs(struct brw_ff_gs_compile *c,
55                                  GLuint nr_verts,
56                                  bool sol_program)
57 {
58    GLuint i = 0,j;
59 
60    /* Register usage is static, precompute here:
61     */
62    c->reg.R0 = retype(brw_vec8_grf(i, 0), BRW_REGISTER_TYPE_UD); i++;
63 
64    /* Streamed vertex buffer indices */
65    if (sol_program)
66       c->reg.SVBI = retype(brw_vec8_grf(i++, 0), BRW_REGISTER_TYPE_UD);
67 
68    /* Payload vertices plus space for more generated vertices:
69     */
70    for (j = 0; j < nr_verts; j++) {
71       c->reg.vertex[j] = brw_vec4_grf(i, 0);
72       i += c->nr_regs;
73    }
74 
75    c->reg.header = retype(brw_vec8_grf(i++, 0), BRW_REGISTER_TYPE_UD);
76    c->reg.temp = retype(brw_vec8_grf(i++, 0), BRW_REGISTER_TYPE_UD);
77 
78    if (sol_program) {
79       c->reg.destination_indices =
80          retype(brw_vec4_grf(i++, 0), BRW_REGISTER_TYPE_UD);
81    }
82 
83    c->prog_data.urb_read_length = c->nr_regs;
84    c->prog_data.total_grf = i;
85 }
86 
87 
88 /**
89  * Set up the initial value of c->reg.header register based on c->reg.R0.
90  *
91  * The following information is passed to the GS thread in R0, and needs to be
92  * included in the first URB_WRITE or FF_SYNC message sent by the GS:
93  *
94  * - DWORD 0 [31:0] handle info (Gen4 only)
95  * - DWORD 5 [7:0] FFTID
96  * - DWORD 6 [31:0] Debug info
97  * - DWORD 7 [31:0] Debug info
98  *
99  * This function sets up the above data by copying by copying the contents of
100  * R0 to the header register.
101  */
brw_ff_gs_initialize_header(struct brw_ff_gs_compile * c)102 static void brw_ff_gs_initialize_header(struct brw_ff_gs_compile *c)
103 {
104    struct brw_codegen *p = &c->func;
105    brw_MOV(p, c->reg.header, c->reg.R0);
106 }
107 
108 /**
109  * Overwrite DWORD 2 of c->reg.header with the given immediate unsigned value.
110  *
111  * In URB_WRITE messages, DWORD 2 contains the fields PrimType, PrimStart,
112  * PrimEnd, Increment CL_INVOCATIONS, and SONumPrimsWritten, many of which we
113  * need to be able to update on a per-vertex basis.
114  */
brw_ff_gs_overwrite_header_dw2(struct brw_ff_gs_compile * c,unsigned dw2)115 static void brw_ff_gs_overwrite_header_dw2(struct brw_ff_gs_compile *c,
116                                            unsigned dw2)
117 {
118    struct brw_codegen *p = &c->func;
119    brw_MOV(p, get_element_ud(c->reg.header, 2), brw_imm_ud(dw2));
120 }
121 
122 /**
123  * Overwrite DWORD 2 of c->reg.header with the primitive type from c->reg.R0.
124  *
125  * When the thread is spawned, GRF 0 contains the primitive type in bits 4:0
126  * of DWORD 2.  URB_WRITE messages need the primitive type in bits 6:2 of
127  * DWORD 2.  So this function extracts the primitive type field, bitshifts it
128  * appropriately, and stores it in c->reg.header.
129  */
brw_ff_gs_overwrite_header_dw2_from_r0(struct brw_ff_gs_compile * c)130 static void brw_ff_gs_overwrite_header_dw2_from_r0(struct brw_ff_gs_compile *c)
131 {
132    struct brw_codegen *p = &c->func;
133    brw_AND(p, get_element_ud(c->reg.header, 2), get_element_ud(c->reg.R0, 2),
134            brw_imm_ud(0x1f));
135    brw_SHL(p, get_element_ud(c->reg.header, 2),
136            get_element_ud(c->reg.header, 2), brw_imm_ud(2));
137 }
138 
139 /**
140  * Apply an additive offset to DWORD 2 of c->reg.header.
141  *
142  * This is used to set/unset the "PrimStart" and "PrimEnd" flags appropriately
143  * for each vertex.
144  */
brw_ff_gs_offset_header_dw2(struct brw_ff_gs_compile * c,int offset)145 static void brw_ff_gs_offset_header_dw2(struct brw_ff_gs_compile *c,
146                                         int offset)
147 {
148    struct brw_codegen *p = &c->func;
149    brw_ADD(p, get_element_d(c->reg.header, 2), get_element_d(c->reg.header, 2),
150            brw_imm_d(offset));
151 }
152 
153 
154 /**
155  * Emit a vertex using the URB_WRITE message.  Use the contents of
156  * c->reg.header for the message header, and the registers starting at \c vert
157  * for the vertex data.
158  *
159  * If \c last is true, then this is the last vertex, so no further URB space
160  * should be allocated, and this message should end the thread.
161  *
162  * If \c last is false, then a new URB entry will be allocated, and its handle
163  * will be stored in DWORD 0 of c->reg.header for use in the next URB_WRITE
164  * message.
165  */
brw_ff_gs_emit_vue(struct brw_ff_gs_compile * c,struct brw_reg vert,bool last)166 static void brw_ff_gs_emit_vue(struct brw_ff_gs_compile *c,
167                                struct brw_reg vert,
168                                bool last)
169 {
170    struct brw_codegen *p = &c->func;
171    int write_offset = 0;
172    bool complete = false;
173 
174    do {
175       /* We can't write more than 14 registers at a time to the URB */
176       int write_len = MIN2(c->nr_regs - write_offset, 14);
177       if (write_len == c->nr_regs - write_offset)
178          complete = true;
179 
180       /* Copy the vertex from vertn into m1..mN+1:
181        */
182       brw_copy8(p, brw_message_reg(1), offset(vert, write_offset), write_len);
183 
184       /* Send the vertex data to the URB.  If this is the last write for this
185        * vertex, then we mark it as complete, and either end the thread or
186        * allocate another vertex URB entry (depending whether this is the last
187        * vertex).
188        */
189       enum brw_urb_write_flags flags;
190       if (!complete)
191          flags = BRW_URB_WRITE_NO_FLAGS;
192       else if (last)
193          flags = BRW_URB_WRITE_EOT_COMPLETE;
194       else
195          flags = BRW_URB_WRITE_ALLOCATE_COMPLETE;
196       brw_urb_WRITE(p,
197                     (flags & BRW_URB_WRITE_ALLOCATE) ? c->reg.temp
198                     : retype(brw_null_reg(), BRW_REGISTER_TYPE_UD),
199                     0,
200                     c->reg.header,
201                     flags,
202                     write_len + 1, /* msg length */
203                     (flags & BRW_URB_WRITE_ALLOCATE) ? 1
204                     : 0, /* response length */
205                     write_offset,  /* urb offset */
206                     BRW_URB_SWIZZLE_NONE);
207       write_offset += write_len;
208    } while (!complete);
209 
210    if (!last) {
211       brw_MOV(p, get_element_ud(c->reg.header, 0),
212               get_element_ud(c->reg.temp, 0));
213    }
214 }
215 
216 /**
217  * Send an FF_SYNC message to ensure that all previously spawned GS threads
218  * have finished sending primitives down the pipeline, and to allocate a URB
219  * entry for the first output vertex.  Only needed on Ironlake+.
220  *
221  * This function modifies c->reg.header: in DWORD 1, it stores num_prim (which
222  * is needed by the FF_SYNC message), and in DWORD 0, it stores the handle to
223  * the allocated URB entry (which will be needed by the URB_WRITE meesage that
224  * follows).
225  */
brw_ff_gs_ff_sync(struct brw_ff_gs_compile * c,int num_prim)226 static void brw_ff_gs_ff_sync(struct brw_ff_gs_compile *c, int num_prim)
227 {
228    struct brw_codegen *p = &c->func;
229 
230    brw_MOV(p, get_element_ud(c->reg.header, 1), brw_imm_ud(num_prim));
231    brw_ff_sync(p,
232                c->reg.temp,
233                0,
234                c->reg.header,
235                1, /* allocate */
236                1, /* response length */
237                0 /* eot */);
238    brw_MOV(p, get_element_ud(c->reg.header, 0),
239            get_element_ud(c->reg.temp, 0));
240 }
241 
242 
243 void
brw_ff_gs_quads(struct brw_ff_gs_compile * c,struct brw_ff_gs_prog_key * key)244 brw_ff_gs_quads(struct brw_ff_gs_compile *c, struct brw_ff_gs_prog_key *key)
245 {
246    brw_ff_gs_alloc_regs(c, 4, false);
247    brw_ff_gs_initialize_header(c);
248    /* Use polygons for correct edgeflag behaviour. Note that vertex 3
249     * is the PV for quads, but vertex 0 for polygons:
250     */
251    if (c->func.devinfo->gen == 5)
252       brw_ff_gs_ff_sync(c, 1);
253    brw_ff_gs_overwrite_header_dw2(
254       c, ((_3DPRIM_POLYGON << URB_WRITE_PRIM_TYPE_SHIFT)
255           | URB_WRITE_PRIM_START));
256    if (key->pv_first) {
257       brw_ff_gs_emit_vue(c, c->reg.vertex[0], 0);
258       brw_ff_gs_overwrite_header_dw2(
259          c, _3DPRIM_POLYGON << URB_WRITE_PRIM_TYPE_SHIFT);
260       brw_ff_gs_emit_vue(c, c->reg.vertex[1], 0);
261       brw_ff_gs_emit_vue(c, c->reg.vertex[2], 0);
262       brw_ff_gs_overwrite_header_dw2(
263          c, ((_3DPRIM_POLYGON << URB_WRITE_PRIM_TYPE_SHIFT)
264              | URB_WRITE_PRIM_END));
265       brw_ff_gs_emit_vue(c, c->reg.vertex[3], 1);
266    }
267    else {
268       brw_ff_gs_emit_vue(c, c->reg.vertex[3], 0);
269       brw_ff_gs_overwrite_header_dw2(
270          c, _3DPRIM_POLYGON << URB_WRITE_PRIM_TYPE_SHIFT);
271       brw_ff_gs_emit_vue(c, c->reg.vertex[0], 0);
272       brw_ff_gs_emit_vue(c, c->reg.vertex[1], 0);
273       brw_ff_gs_overwrite_header_dw2(
274          c, ((_3DPRIM_POLYGON << URB_WRITE_PRIM_TYPE_SHIFT)
275              | URB_WRITE_PRIM_END));
276       brw_ff_gs_emit_vue(c, c->reg.vertex[2], 1);
277    }
278 }
279 
280 void
brw_ff_gs_quad_strip(struct brw_ff_gs_compile * c,struct brw_ff_gs_prog_key * key)281 brw_ff_gs_quad_strip(struct brw_ff_gs_compile *c,
282                      struct brw_ff_gs_prog_key *key)
283 {
284    brw_ff_gs_alloc_regs(c, 4, false);
285    brw_ff_gs_initialize_header(c);
286 
287    if (c->func.devinfo->gen == 5)
288       brw_ff_gs_ff_sync(c, 1);
289    brw_ff_gs_overwrite_header_dw2(
290       c, ((_3DPRIM_POLYGON << URB_WRITE_PRIM_TYPE_SHIFT)
291           | URB_WRITE_PRIM_START));
292    if (key->pv_first) {
293       brw_ff_gs_emit_vue(c, c->reg.vertex[0], 0);
294       brw_ff_gs_overwrite_header_dw2(
295          c, _3DPRIM_POLYGON << URB_WRITE_PRIM_TYPE_SHIFT);
296       brw_ff_gs_emit_vue(c, c->reg.vertex[1], 0);
297       brw_ff_gs_emit_vue(c, c->reg.vertex[2], 0);
298       brw_ff_gs_overwrite_header_dw2(
299          c, ((_3DPRIM_POLYGON << URB_WRITE_PRIM_TYPE_SHIFT)
300              | URB_WRITE_PRIM_END));
301       brw_ff_gs_emit_vue(c, c->reg.vertex[3], 1);
302    }
303    else {
304       brw_ff_gs_emit_vue(c, c->reg.vertex[2], 0);
305       brw_ff_gs_overwrite_header_dw2(
306          c, _3DPRIM_POLYGON << URB_WRITE_PRIM_TYPE_SHIFT);
307       brw_ff_gs_emit_vue(c, c->reg.vertex[3], 0);
308       brw_ff_gs_emit_vue(c, c->reg.vertex[0], 0);
309       brw_ff_gs_overwrite_header_dw2(
310          c, ((_3DPRIM_POLYGON << URB_WRITE_PRIM_TYPE_SHIFT)
311              | URB_WRITE_PRIM_END));
312       brw_ff_gs_emit_vue(c, c->reg.vertex[1], 1);
313    }
314 }
315 
brw_ff_gs_lines(struct brw_ff_gs_compile * c)316 void brw_ff_gs_lines(struct brw_ff_gs_compile *c)
317 {
318    brw_ff_gs_alloc_regs(c, 2, false);
319    brw_ff_gs_initialize_header(c);
320 
321    if (c->func.devinfo->gen == 5)
322       brw_ff_gs_ff_sync(c, 1);
323    brw_ff_gs_overwrite_header_dw2(
324       c, ((_3DPRIM_LINESTRIP << URB_WRITE_PRIM_TYPE_SHIFT)
325           | URB_WRITE_PRIM_START));
326    brw_ff_gs_emit_vue(c, c->reg.vertex[0], 0);
327    brw_ff_gs_overwrite_header_dw2(
328       c, ((_3DPRIM_LINESTRIP << URB_WRITE_PRIM_TYPE_SHIFT)
329           | URB_WRITE_PRIM_END));
330    brw_ff_gs_emit_vue(c, c->reg.vertex[1], 1);
331 }
332 
333 /**
334  * Generate the geometry shader program used on Gen6 to perform stream output
335  * (transform feedback).
336  */
337 void
gen6_sol_program(struct brw_ff_gs_compile * c,struct brw_ff_gs_prog_key * key,unsigned num_verts,bool check_edge_flags)338 gen6_sol_program(struct brw_ff_gs_compile *c, struct brw_ff_gs_prog_key *key,
339 	         unsigned num_verts, bool check_edge_flags)
340 {
341    struct brw_codegen *p = &c->func;
342    brw_inst *inst;
343    c->prog_data.svbi_postincrement_value = num_verts;
344 
345    brw_ff_gs_alloc_regs(c, num_verts, true);
346    brw_ff_gs_initialize_header(c);
347 
348    if (key->num_transform_feedback_bindings > 0) {
349       unsigned vertex, binding;
350       struct brw_reg destination_indices_uw =
351          vec8(retype(c->reg.destination_indices, BRW_REGISTER_TYPE_UW));
352 
353       /* Note: since we use the binding table to keep track of buffer offsets
354        * and stride, the GS doesn't need to keep track of a separate pointer
355        * into each buffer; it uses a single pointer which increments by 1 for
356        * each vertex.  So we use SVBI0 for this pointer, regardless of whether
357        * transform feedback is in interleaved or separate attribs mode.
358        *
359        * Make sure that the buffers have enough room for all the vertices.
360        */
361       brw_ADD(p, get_element_ud(c->reg.temp, 0),
362 	         get_element_ud(c->reg.SVBI, 0), brw_imm_ud(num_verts));
363       brw_CMP(p, vec1(brw_null_reg()), BRW_CONDITIONAL_LE,
364 	         get_element_ud(c->reg.temp, 0),
365 	         get_element_ud(c->reg.SVBI, 4));
366       brw_IF(p, BRW_EXECUTE_1);
367 
368       /* Compute the destination indices to write to.  Usually we use SVBI[0]
369        * + (0, 1, 2).  However, for odd-numbered triangles in tristrips, the
370        * vertices come down the pipeline in reversed winding order, so we need
371        * to flip the order when writing to the transform feedback buffer.  To
372        * ensure that flatshading accuracy is preserved, we need to write them
373        * in order SVBI[0] + (0, 2, 1) if we're using the first provoking
374        * vertex convention, and in order SVBI[0] + (1, 0, 2) if we're using
375        * the last provoking vertex convention.
376        *
377        * Note: since brw_imm_v can only be used in instructions in
378        * packed-word execution mode, and SVBI is a double-word, we need to
379        * first move the appropriate immediate constant ((0, 1, 2), (0, 2, 1),
380        * or (1, 0, 2)) to the destination_indices register, and then add SVBI
381        * using a separate instruction.  Also, since the immediate constant is
382        * expressed as packed words, and we need to load double-words into
383        * destination_indices, we need to intersperse zeros to fill the upper
384        * halves of each double-word.
385        */
386       brw_MOV(p, destination_indices_uw,
387               brw_imm_v(0x00020100)); /* (0, 1, 2) */
388       if (num_verts == 3) {
389          /* Get primitive type into temp register. */
390          brw_AND(p, get_element_ud(c->reg.temp, 0),
391                  get_element_ud(c->reg.R0, 2), brw_imm_ud(0x1f));
392 
393          /* Test if primitive type is TRISTRIP_REVERSE.  We need to do this as
394           * an 8-wide comparison so that the conditional MOV that follows
395           * moves all 8 words correctly.
396           */
397          brw_CMP(p, vec8(brw_null_reg()), BRW_CONDITIONAL_EQ,
398                  get_element_ud(c->reg.temp, 0),
399                  brw_imm_ud(_3DPRIM_TRISTRIP_REVERSE));
400 
401          /* If so, then overwrite destination_indices_uw with the appropriate
402           * reordering.
403           */
404          inst = brw_MOV(p, destination_indices_uw,
405                         brw_imm_v(key->pv_first ? 0x00010200    /* (0, 2, 1) */
406                                                 : 0x00020001)); /* (1, 0, 2) */
407          brw_inst_set_pred_control(p->devinfo, inst, BRW_PREDICATE_NORMAL);
408       }
409 
410       assert(c->reg.destination_indices.width == BRW_EXECUTE_4);
411       brw_push_insn_state(p);
412       brw_set_default_exec_size(p, BRW_EXECUTE_4);
413       brw_ADD(p, c->reg.destination_indices,
414               c->reg.destination_indices, get_element_ud(c->reg.SVBI, 0));
415       brw_pop_insn_state(p);
416       /* For each vertex, generate code to output each varying using the
417        * appropriate binding table entry.
418        */
419       for (vertex = 0; vertex < num_verts; ++vertex) {
420          /* Set up the correct destination index for this vertex */
421          brw_MOV(p, get_element_ud(c->reg.header, 5),
422                  get_element_ud(c->reg.destination_indices, vertex));
423 
424          for (binding = 0; binding < key->num_transform_feedback_bindings;
425               ++binding) {
426             unsigned char varying =
427                key->transform_feedback_bindings[binding];
428             unsigned char slot = c->vue_map.varying_to_slot[varying];
429             /* From the Sandybridge PRM, Volume 2, Part 1, Section 4.5.1:
430              *
431              *   "Prior to End of Thread with a URB_WRITE, the kernel must
432              *   ensure that all writes are complete by sending the final
433              *   write as a committed write."
434              */
435             bool final_write =
436                binding == key->num_transform_feedback_bindings - 1 &&
437                vertex == num_verts - 1;
438             struct brw_reg vertex_slot = c->reg.vertex[vertex];
439             vertex_slot.nr += slot / 2;
440             vertex_slot.subnr = (slot % 2) * 16;
441             /* gl_PointSize is stored in VARYING_SLOT_PSIZ.w. */
442             vertex_slot.swizzle = varying == VARYING_SLOT_PSIZ
443                ? BRW_SWIZZLE_WWWW : key->transform_feedback_swizzles[binding];
444             brw_set_default_access_mode(p, BRW_ALIGN_16);
445             brw_push_insn_state(p);
446             brw_set_default_exec_size(p, BRW_EXECUTE_4);
447 
448             brw_MOV(p, stride(c->reg.header, 4, 4, 1),
449                     retype(vertex_slot, BRW_REGISTER_TYPE_UD));
450             brw_pop_insn_state(p);
451 
452             brw_set_default_access_mode(p, BRW_ALIGN_1);
453             brw_svb_write(p,
454                           final_write ? c->reg.temp : brw_null_reg(), /* dest */
455                           1, /* msg_reg_nr */
456                           c->reg.header, /* src0 */
457                           SURF_INDEX_GEN6_SOL_BINDING(binding), /* binding_table_index */
458                           final_write); /* send_commit_msg */
459          }
460       }
461       brw_ENDIF(p);
462 
463       /* Now, reinitialize the header register from R0 to restore the parts of
464        * the register that we overwrote while streaming out transform feedback
465        * data.
466        */
467       brw_ff_gs_initialize_header(c);
468 
469       /* Finally, wait for the write commit to occur so that we can proceed to
470        * other things safely.
471        *
472        * From the Sandybridge PRM, Volume 4, Part 1, Section 3.3:
473        *
474        *   The write commit does not modify the destination register, but
475        *   merely clears the dependency associated with the destination
476        *   register. Thus, a simple “mov” instruction using the register as a
477        *   source is sufficient to wait for the write commit to occur.
478        */
479       brw_MOV(p, c->reg.temp, c->reg.temp);
480    }
481 
482    brw_ff_gs_ff_sync(c, 1);
483 
484    brw_ff_gs_overwrite_header_dw2_from_r0(c);
485    switch (num_verts) {
486    case 1:
487       brw_ff_gs_offset_header_dw2(c,
488                                   URB_WRITE_PRIM_START | URB_WRITE_PRIM_END);
489       brw_ff_gs_emit_vue(c, c->reg.vertex[0], true);
490       break;
491    case 2:
492       brw_ff_gs_offset_header_dw2(c, URB_WRITE_PRIM_START);
493       brw_ff_gs_emit_vue(c, c->reg.vertex[0], false);
494       brw_ff_gs_offset_header_dw2(c,
495                                   URB_WRITE_PRIM_END - URB_WRITE_PRIM_START);
496       brw_ff_gs_emit_vue(c, c->reg.vertex[1], true);
497       break;
498    case 3:
499       if (check_edge_flags) {
500          /* Only emit vertices 0 and 1 if this is the first triangle of the
501           * polygon.  Otherwise they are redundant.
502           */
503          brw_AND(p, retype(brw_null_reg(), BRW_REGISTER_TYPE_UD),
504                  get_element_ud(c->reg.R0, 2),
505                  brw_imm_ud(BRW_GS_EDGE_INDICATOR_0));
506          brw_inst_set_cond_modifier(p->devinfo, brw_last_inst, BRW_CONDITIONAL_NZ);
507          brw_IF(p, BRW_EXECUTE_1);
508       }
509       brw_ff_gs_offset_header_dw2(c, URB_WRITE_PRIM_START);
510       brw_ff_gs_emit_vue(c, c->reg.vertex[0], false);
511       brw_ff_gs_offset_header_dw2(c, -URB_WRITE_PRIM_START);
512       brw_ff_gs_emit_vue(c, c->reg.vertex[1], false);
513       if (check_edge_flags) {
514          brw_ENDIF(p);
515          /* Only emit vertex 2 in PRIM_END mode if this is the last triangle
516           * of the polygon.  Otherwise leave the primitive incomplete because
517           * there are more polygon vertices coming.
518           */
519          brw_AND(p, retype(brw_null_reg(), BRW_REGISTER_TYPE_UD),
520                  get_element_ud(c->reg.R0, 2),
521                  brw_imm_ud(BRW_GS_EDGE_INDICATOR_1));
522          brw_inst_set_cond_modifier(p->devinfo, brw_last_inst, BRW_CONDITIONAL_NZ);
523          brw_set_default_predicate_control(p, BRW_PREDICATE_NORMAL);
524       }
525       brw_ff_gs_offset_header_dw2(c, URB_WRITE_PRIM_END);
526       brw_set_default_predicate_control(p, BRW_PREDICATE_NONE);
527       brw_ff_gs_emit_vue(c, c->reg.vertex[2], true);
528       break;
529    }
530 }
531