src/compiler/nir/nir_lower_clip.c - third_party/mesa - Git at Google

 /*
  * Copyright © 2015 Red Hat
  *
  * Permission is hereby granted, free of charge, to any person obtaining a
  * copy of this software and associated documentation files (the "Software"),
  * to deal in the Software without restriction, including without limitation
  * the rights to use, copy, modify, merge, publish, distribute, sublicense,
  * and/or sell copies of the Software, and to permit persons to whom the
  * Software is furnished to do so, subject to the following conditions:
  *
  * The above copyright notice and this permission notice (including the next
  * paragraph) shall be included in all copies or substantial portions of the
  * Software.
  *
  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
  * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
  * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
  * IN THE SOFTWARE.
  *
  * Authors:
  *    Rob Clark <robclark@freedesktop.org>
  */

 #include "nir.h"
 #include "nir_builder.h"

 #define MAX_CLIP_PLANES 8

 /* Generates the lowering code for user-clip-planes, generating CLIPDIST
  * from UCP[n] + CLIPVERTEX or POSITION.  Additionally, an optional pass
  * for fragment shaders to insert conditional kills based on the inter-
  * polated CLIPDIST
  *
  * NOTE: should be run after nir_lower_outputs_to_temporaries() (or at
  * least in scenarios where you can count on each output written once
  * and only once).
  */


 static nir_variable *
 create_clipdist_var(nir_shader *shader, unsigned drvloc,
                     bool output, gl_varying_slot slot)
 {
    nir_variable *var = rzalloc(shader, nir_variable);

    var->data.driver_location = drvloc;
    var->type = glsl_vec4_type();
    var->data.mode = output ? nir_var_shader_out : nir_var_shader_in;
    var->name = ralloc_asprintf(var, "clipdist_%d", drvloc);
    var->data.index = 0;
    var->data.location = slot;

    if (output) {
       exec_list_push_tail(&shader->outputs, &var->node);
       shader->num_outputs++; /* TODO use type_size() */
    }
    else {
       exec_list_push_tail(&shader->inputs, &var->node);
       shader->num_inputs++;  /* TODO use type_size() */
    }
    return var;
 }

 static void
 create_clipdist_vars(nir_shader *shader, nir_variable **io_vars,
                      unsigned ucp_enables, int *drvloc, bool output)
 {
    if (ucp_enables & 0x0f)
       io_vars[0] =
          create_clipdist_var(shader, ++(*drvloc), output,
                              VARYING_SLOT_CLIP_DIST0);
    if (ucp_enables & 0xf0)
       io_vars[1] =
          create_clipdist_var(shader, ++(*drvloc), output,
                              VARYING_SLOT_CLIP_DIST1);
 }

 static void
 store_clipdist_output(nir_builder *b, nir_variable *out, nir_ssa_def **val)
 {
    nir_intrinsic_instr *store;

    store = nir_intrinsic_instr_create(b->shader, nir_intrinsic_store_output);
    store->num_components = 4;
    nir_intrinsic_set_base(store, out->data.driver_location);
    nir_intrinsic_set_write_mask(store, 0xf);
    store->src[0].ssa = nir_vec4(b, val[0], val[1], val[2], val[3]);
    store->src[0].is_ssa = true;
    store->src[1] = nir_src_for_ssa(nir_imm_int(b, 0));
    nir_builder_instr_insert(b, &store->instr);
 }

 static void
 load_clipdist_input(nir_builder *b, nir_variable *in, nir_ssa_def **val)
 {
    nir_intrinsic_instr *load;

    load = nir_intrinsic_instr_create(b->shader, nir_intrinsic_load_input);
    load->num_components = 4;
    nir_intrinsic_set_base(load, in->data.driver_location);
    load->src[0] = nir_src_for_ssa(nir_imm_int(b, 0));
    nir_ssa_dest_init(&load->instr, &load->dest, 4, 32, NULL);
    nir_builder_instr_insert(b, &load->instr);

    val[0] = nir_channel(b, &load->dest.ssa, 0);
    val[1] = nir_channel(b, &load->dest.ssa, 1);
    val[2] = nir_channel(b, &load->dest.ssa, 2);
    val[3] = nir_channel(b, &load->dest.ssa, 3);
 }

 static nir_ssa_def *
 find_output_in_block(nir_block *block, unsigned drvloc)
 {
    nir_foreach_instr(instr, block) {

       if (instr->type == nir_instr_type_intrinsic) {
          nir_intrinsic_instr *intr = nir_instr_as_intrinsic(instr);
          if ((intr->intrinsic == nir_intrinsic_store_output) &&
              nir_intrinsic_base(intr) == drvloc) {
             assert(intr->src[0].is_ssa);
             assert(nir_src_is_const(intr->src[1]));
             return intr->src[0].ssa;
          }
       }
    }

    return NULL;
 }

 /* TODO: maybe this would be a useful helper?
  * NOTE: assumes each output is written exactly once (and unconditionally)
  * so if needed nir_lower_outputs_to_temporaries()
  */
 static nir_ssa_def *
 find_output(nir_shader *shader, unsigned drvloc)
 {
    nir_ssa_def *def = NULL;
    nir_foreach_function(function, shader) {
       if (function->impl) {
          nir_foreach_block_reverse(block, function->impl) {
             nir_ssa_def *new_def = find_output_in_block(block, drvloc);
             assert(!(new_def && def));
             def = new_def;
 #if !defined(DEBUG)
             /* for debug builds, scan entire shader to assert
              * if output is written multiple times.  For release
              * builds just assume all is well and bail when we
              * find first:
              */
             if (def)
                break;
 #endif
          }
       }
    }

    return def;
 }

 static bool
 find_clipvertex_and_position_outputs(nir_shader *shader,
                                      nir_variable **clipvertex,
                                      nir_variable **position)
 {
    nir_foreach_variable(var, &shader->outputs) {
       switch (var->data.location) {
       case VARYING_SLOT_POS:
          *position = var;
          break;
       case VARYING_SLOT_CLIP_VERTEX:
          *clipvertex = var;
          break;
       case VARYING_SLOT_CLIP_DIST0:
       case VARYING_SLOT_CLIP_DIST1:
          /* if shader is already writing CLIPDIST, then
           * there should be no user-clip-planes to deal
           * with.
           *
           * We assume nir_remove_dead_variables has removed the clipdist
           * variables if they're not written.
           */
          return false;
       }
    }

    return *clipvertex || *position;
 }

 static void
 lower_clip_outputs(nir_builder *b, nir_variable *position,
                    nir_variable *clipvertex, nir_variable **out,
                    unsigned ucp_enables, bool use_vars)
 {
    nir_ssa_def *clipdist[MAX_CLIP_PLANES];
    nir_ssa_def *cv;

    if (use_vars) {
       cv = nir_load_var(b, clipvertex ? clipvertex : position);

       if (clipvertex) {
          exec_node_remove(&clipvertex->node);
          clipvertex->data.mode = nir_var_shader_temp;
          exec_list_push_tail(&b->shader->globals, &clipvertex->node);
       }
    } else {
       if (clipvertex)
          cv = find_output(b->shader, clipvertex->data.driver_location);
       else {
          assert(position);
          cv = find_output(b->shader, position->data.driver_location);
       }
    }

    for (int plane = 0; plane < MAX_CLIP_PLANES; plane++) {
       if (ucp_enables & (1 << plane)) {
          nir_ssa_def *ucp = nir_load_user_clip_plane(b, plane);

          /* calculate clipdist[plane] - dot(ucp, cv): */
          clipdist[plane] = nir_fdot4(b, ucp, cv);
       } else {
          /* 0.0 == don't-clip == disabled: */
          clipdist[plane] = nir_imm_float(b, 0.0);
       }
    }

    if (use_vars) {
       if (ucp_enables & 0x0f)
          nir_store_var(b, out[0], nir_vec(b, clipdist, 4), 0xf);
       if (ucp_enables & 0xf0)
          nir_store_var(b, out[1], nir_vec(b, &clipdist[4], 4), 0xf);
    } else {
       if (ucp_enables & 0x0f)
          store_clipdist_output(b, out[0], &clipdist[0]);
       if (ucp_enables & 0xf0)
          store_clipdist_output(b, out[1], &clipdist[4]);
    }
 }

 /*
  * VS lowering
  */

 /* ucp_enables is bitmask of enabled ucps.  Actual ucp values are
  * passed in to shader via user_clip_plane system-values
  *
  * If use_vars is true, the pass will use variable loads and stores instead
  * of working with store_output intrinsics.
  */
 bool
 nir_lower_clip_vs(nir_shader *shader, unsigned ucp_enables, bool use_vars)
 {
    nir_function_impl *impl = nir_shader_get_entrypoint(shader);
    nir_builder b;
    int maxloc = -1;
    nir_variable *position = NULL;
    nir_variable *clipvertex = NULL;
    nir_variable *out[2] = { NULL };

    if (!ucp_enables)
       return false;

    nir_builder_init(&b, impl);

    /* NIR should ensure that, even in case of loops/if-else, there
     * should be only a single predecessor block to end_block, which
     * makes the perfect place to insert the clipdist calculations.
     *
     * NOTE: in case of early returns, these would have to be lowered
     * to jumps to end_block predecessor in a previous pass.  Not sure
     * if there is a good way to sanity check this, but for now the
     * users of this pass don't support sub-routines.
     */
    assert(impl->end_block->predecessors->entries == 1);
    b.cursor = nir_after_cf_list(&impl->body);

    /* find clipvertex/position outputs */
    if (!find_clipvertex_and_position_outputs(shader, &clipvertex, &position))
       return false;

    /* insert CLIPDIST outputs */
    create_clipdist_vars(shader, out, ucp_enables, &maxloc, true);

    lower_clip_outputs(&b, position, clipvertex, out, ucp_enables, use_vars);

    nir_metadata_preserve(impl, nir_metadata_dominance);

    return true;
 }

 static void
 lower_clip_in_gs_block(nir_builder *b, nir_block *block, nir_variable *position,
                        nir_variable *clipvertex, nir_variable **out,
                        unsigned ucp_enables)
 {
    nir_foreach_instr_safe(instr, block) {
       if (instr->type != nir_instr_type_intrinsic)
          continue;

       nir_intrinsic_instr *intrin = nir_instr_as_intrinsic(instr);
       switch (intrin->intrinsic) {
       case nir_intrinsic_emit_vertex_with_counter:
       case nir_intrinsic_emit_vertex:
          b->cursor = nir_before_instr(instr);
          lower_clip_outputs(b, position, clipvertex, out, ucp_enables, true);
          break;
       default:
          /* not interesting; skip this */
          break;
       }
    }
 }

 /*
  * GS lowering
  */

 bool
 nir_lower_clip_gs(nir_shader *shader, unsigned ucp_enables)
 {
    nir_function_impl *impl = nir_shader_get_entrypoint(shader);
    nir_builder b;
    int maxloc = -1;
    nir_variable *position = NULL;
    nir_variable *clipvertex = NULL;
    nir_variable *out[2] = { NULL };

    if (!ucp_enables)
       return false;

    /* find clipvertex/position outputs */
    if (!find_clipvertex_and_position_outputs(shader, &clipvertex, &position))
       return false;

    /* insert CLIPDIST outputs */
    create_clipdist_vars(shader, out, ucp_enables, &maxloc, true);

    nir_builder_init(&b, impl);

    nir_foreach_block(block, impl)
       lower_clip_in_gs_block(&b, block, position, clipvertex, out, ucp_enables);

    nir_metadata_preserve(impl, nir_metadata_dominance);

    return true;
 }

 /*
  * FS lowering
  */

 static void
 lower_clip_fs(nir_function_impl *impl, unsigned ucp_enables,
               nir_variable **in)
 {
    nir_ssa_def *clipdist[MAX_CLIP_PLANES];
    nir_builder b;

    nir_builder_init(&b, impl);
    b.cursor = nir_before_cf_list(&impl->body);

    if (ucp_enables & 0x0f)
       load_clipdist_input(&b, in[0], &clipdist[0]);
    if (ucp_enables & 0xf0)
       load_clipdist_input(&b, in[1], &clipdist[4]);

    for (int plane = 0; plane < MAX_CLIP_PLANES; plane++) {
       if (ucp_enables & (1 << plane)) {
          nir_intrinsic_instr *discard;
          nir_ssa_def *cond;

          cond = nir_flt(&b, clipdist[plane], nir_imm_float(&b, 0.0));

          discard = nir_intrinsic_instr_create(b.shader,
                                               nir_intrinsic_discard_if);
          discard->src[0] = nir_src_for_ssa(cond);
          nir_builder_instr_insert(&b, &discard->instr);

          b.shader->info.fs.uses_discard = true;
       }
    }

    nir_metadata_preserve(impl, nir_metadata_dominance);
 }

 /* insert conditional kill based on interpolated CLIPDIST
  */
 bool
 nir_lower_clip_fs(nir_shader *shader, unsigned ucp_enables)
 {
    nir_variable *in[2];
    int maxloc = -1;

    if (!ucp_enables)
       return false;

    nir_foreach_variable(var, &shader->inputs) {
       int loc = var->data.driver_location;

       /* keep track of last used driver-location.. we'll be
        * appending CLIP_DIST0/CLIP_DIST1 after last existing
        * input:
        */
       maxloc = MAX2(maxloc, loc);
    }

    /* The shader won't normally have CLIPDIST inputs, so we
     * must add our own:
     */
    /* insert CLIPDIST inputs */
    create_clipdist_vars(shader, in, ucp_enables, &maxloc, false);

    nir_foreach_function(function, shader) {
       if (!strcmp(function->name, "main"))
          lower_clip_fs(function->impl, ucp_enables, in);
    }

    return true;
 }
	/*
	* Copyright © 2015 Red Hat
	*
	* Permission is hereby granted, free of charge, to any person obtaining a
	* copy of this software and associated documentation files (the "Software"),
	* to deal in the Software without restriction, including without limitation
	* the rights to use, copy, modify, merge, publish, distribute, sublicense,
	* and/or sell copies of the Software, and to permit persons to whom the
	* Software is furnished to do so, subject to the following conditions:
	*
	* The above copyright notice and this permission notice (including the next
	* paragraph) shall be included in all copies or substantial portions of the
	* Software.
	*
	* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
	* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
	* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
	* THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
	* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
	* FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
	* IN THE SOFTWARE.
	*
	* Authors:
	* Rob Clark <robclark@freedesktop.org>
	*/

	#include "nir.h"
	#include "nir_builder.h"

	#define MAX_CLIP_PLANES 8

	/* Generates the lowering code for user-clip-planes, generating CLIPDIST
	* from UCP[n] + CLIPVERTEX or POSITION. Additionally, an optional pass
	* for fragment shaders to insert conditional kills based on the inter-
	* polated CLIPDIST
	*
	* NOTE: should be run after nir_lower_outputs_to_temporaries() (or at
	* least in scenarios where you can count on each output written once
	* and only once).
	*/


	static nir_variable *
	create_clipdist_var(nir_shader *shader, unsigned drvloc,
	bool output, gl_varying_slot slot)
	{
	nir_variable *var = rzalloc(shader, nir_variable);

	var->data.driver_location = drvloc;
	var->type = glsl_vec4_type();
	var->data.mode = output ? nir_var_shader_out : nir_var_shader_in;
	var->name = ralloc_asprintf(var, "clipdist_%d", drvloc);
	var->data.index = 0;
	var->data.location = slot;

	if (output) {
	exec_list_push_tail(&shader->outputs, &var->node);
	shader->num_outputs++; /* TODO use type_size() */
	}
	else {
	exec_list_push_tail(&shader->inputs, &var->node);
	shader->num_inputs++; /* TODO use type_size() */
	}
	return var;
	}

	static void
	create_clipdist_vars(nir_shader shader, nir_variable *io_vars,
	unsigned ucp_enables, int *drvloc, bool output)
	{
	if (ucp_enables & 0x0f)
	io_vars[0] =
	create_clipdist_var(shader, ++(*drvloc), output,
	VARYING_SLOT_CLIP_DIST0);
	if (ucp_enables & 0xf0)
	io_vars[1] =
	create_clipdist_var(shader, ++(*drvloc), output,
	VARYING_SLOT_CLIP_DIST1);
	}

	static void
	store_clipdist_output(nir_builder b, nir_variable out, nir_ssa_def **val)
	{
	nir_intrinsic_instr *store;

	store = nir_intrinsic_instr_create(b->shader, nir_intrinsic_store_output);
	store->num_components = 4;
	nir_intrinsic_set_base(store, out->data.driver_location);
	nir_intrinsic_set_write_mask(store, 0xf);
	store->src[0].ssa = nir_vec4(b, val[0], val[1], val[2], val[3]);
	store->src[0].is_ssa = true;
	store->src[1] = nir_src_for_ssa(nir_imm_int(b, 0));
	nir_builder_instr_insert(b, &store->instr);
	}

	static void
	load_clipdist_input(nir_builder b, nir_variable in, nir_ssa_def **val)
	{
	nir_intrinsic_instr *load;

	load = nir_intrinsic_instr_create(b->shader, nir_intrinsic_load_input);
	load->num_components = 4;
	nir_intrinsic_set_base(load, in->data.driver_location);
	load->src[0] = nir_src_for_ssa(nir_imm_int(b, 0));
	nir_ssa_dest_init(&load->instr, &load->dest, 4, 32, NULL);
	nir_builder_instr_insert(b, &load->instr);

	val[0] = nir_channel(b, &load->dest.ssa, 0);
	val[1] = nir_channel(b, &load->dest.ssa, 1);
	val[2] = nir_channel(b, &load->dest.ssa, 2);
	val[3] = nir_channel(b, &load->dest.ssa, 3);
	}

	static nir_ssa_def *
	find_output_in_block(nir_block *block, unsigned drvloc)
	{
	nir_foreach_instr(instr, block) {

	if (instr->type == nir_instr_type_intrinsic) {
	nir_intrinsic_instr *intr = nir_instr_as_intrinsic(instr);
	if ((intr->intrinsic == nir_intrinsic_store_output) &&
	nir_intrinsic_base(intr) == drvloc) {
	assert(intr->src[0].is_ssa);
	assert(nir_src_is_const(intr->src[1]));
	return intr->src[0].ssa;
	}
	}
	}

	return NULL;
	}

	/* TODO: maybe this would be a useful helper?
	* NOTE: assumes each output is written exactly once (and unconditionally)
	* so if needed nir_lower_outputs_to_temporaries()
	*/
	static nir_ssa_def *
	find_output(nir_shader *shader, unsigned drvloc)
	{
	nir_ssa_def *def = NULL;
	nir_foreach_function(function, shader) {
	if (function->impl) {
	nir_foreach_block_reverse(block, function->impl) {
	nir_ssa_def *new_def = find_output_in_block(block, drvloc);
	assert(!(new_def && def));
	def = new_def;
	#if !defined(DEBUG)
	/* for debug builds, scan entire shader to assert
	* if output is written multiple times. For release
	* builds just assume all is well and bail when we
	* find first:
	*/
	if (def)
	break;
	#endif
	}
	}
	}

	return def;
	}

	static bool
	find_clipvertex_and_position_outputs(nir_shader *shader,
	nir_variable **clipvertex,
	nir_variable **position)
	{
	nir_foreach_variable(var, &shader->outputs) {
	switch (var->data.location) {
	case VARYING_SLOT_POS:
	*position = var;
	break;
	case VARYING_SLOT_CLIP_VERTEX:
	*clipvertex = var;
	break;
	case VARYING_SLOT_CLIP_DIST0:
	case VARYING_SLOT_CLIP_DIST1:
	/* if shader is already writing CLIPDIST, then
	* there should be no user-clip-planes to deal
	* with.
	*
	* We assume nir_remove_dead_variables has removed the clipdist
	* variables if they're not written.
	*/
	return false;
	}
	}

	return clipvertex \|\| position;
	}

	static void
	lower_clip_outputs(nir_builder b, nir_variable position,
	nir_variable clipvertex, nir_variable *out,
	unsigned ucp_enables, bool use_vars)
	{
	nir_ssa_def *clipdist[MAX_CLIP_PLANES];
	nir_ssa_def *cv;

	if (use_vars) {
	cv = nir_load_var(b, clipvertex ? clipvertex : position);

	if (clipvertex) {
	exec_node_remove(&clipvertex->node);
	clipvertex->data.mode = nir_var_shader_temp;
	exec_list_push_tail(&b->shader->globals, &clipvertex->node);
	}
	} else {
	if (clipvertex)
	cv = find_output(b->shader, clipvertex->data.driver_location);
	else {
	assert(position);
	cv = find_output(b->shader, position->data.driver_location);
	}
	}

	for (int plane = 0; plane < MAX_CLIP_PLANES; plane++) {
	if (ucp_enables & (1 << plane)) {
	nir_ssa_def *ucp = nir_load_user_clip_plane(b, plane);

	/* calculate clipdist[plane] - dot(ucp, cv): */
	clipdist[plane] = nir_fdot4(b, ucp, cv);
	} else {
	/* 0.0 == don't-clip == disabled: */
	clipdist[plane] = nir_imm_float(b, 0.0);
	}
	}

	if (use_vars) {
	if (ucp_enables & 0x0f)
	nir_store_var(b, out[0], nir_vec(b, clipdist, 4), 0xf);
	if (ucp_enables & 0xf0)
	nir_store_var(b, out[1], nir_vec(b, &clipdist[4], 4), 0xf);
	} else {
	if (ucp_enables & 0x0f)
	store_clipdist_output(b, out[0], &clipdist[0]);
	if (ucp_enables & 0xf0)
	store_clipdist_output(b, out[1], &clipdist[4]);
	}
	}

	/*
	* VS lowering
	*/

	/* ucp_enables is bitmask of enabled ucps. Actual ucp values are
	* passed in to shader via user_clip_plane system-values
	*
	* If use_vars is true, the pass will use variable loads and stores instead
	* of working with store_output intrinsics.
	*/
	bool
	nir_lower_clip_vs(nir_shader *shader, unsigned ucp_enables, bool use_vars)
	{
	nir_function_impl *impl = nir_shader_get_entrypoint(shader);
	nir_builder b;
	int maxloc = -1;
	nir_variable *position = NULL;
	nir_variable *clipvertex = NULL;
	nir_variable *out[2] = { NULL };

	if (!ucp_enables)
	return false;

	nir_builder_init(&b, impl);

	/* NIR should ensure that, even in case of loops/if-else, there
	* should be only a single predecessor block to end_block, which
	* makes the perfect place to insert the clipdist calculations.
	*
	* NOTE: in case of early returns, these would have to be lowered
	* to jumps to end_block predecessor in a previous pass. Not sure
	* if there is a good way to sanity check this, but for now the
	* users of this pass don't support sub-routines.
	*/
	assert(impl->end_block->predecessors->entries == 1);
	b.cursor = nir_after_cf_list(&impl->body);

	/* find clipvertex/position outputs */
	if (!find_clipvertex_and_position_outputs(shader, &clipvertex, &position))
	return false;

	/* insert CLIPDIST outputs */
	create_clipdist_vars(shader, out, ucp_enables, &maxloc, true);

	lower_clip_outputs(&b, position, clipvertex, out, ucp_enables, use_vars);

	nir_metadata_preserve(impl, nir_metadata_dominance);

	return true;
	}

	static void
	lower_clip_in_gs_block(nir_builder b, nir_block block, nir_variable *position,
	nir_variable clipvertex, nir_variable *out,
	unsigned ucp_enables)
	{
	nir_foreach_instr_safe(instr, block) {
	if (instr->type != nir_instr_type_intrinsic)
	continue;

	nir_intrinsic_instr *intrin = nir_instr_as_intrinsic(instr);
	switch (intrin->intrinsic) {
	case nir_intrinsic_emit_vertex_with_counter:
	case nir_intrinsic_emit_vertex:
	b->cursor = nir_before_instr(instr);
	lower_clip_outputs(b, position, clipvertex, out, ucp_enables, true);
	break;
	default:
	/* not interesting; skip this */
	break;
	}
	}
	}

	/*
	* GS lowering
	*/

	bool
	nir_lower_clip_gs(nir_shader *shader, unsigned ucp_enables)
	{
	nir_function_impl *impl = nir_shader_get_entrypoint(shader);
	nir_builder b;
	int maxloc = -1;
	nir_variable *position = NULL;
	nir_variable *clipvertex = NULL;
	nir_variable *out[2] = { NULL };

	if (!ucp_enables)
	return false;

	/* find clipvertex/position outputs */
	if (!find_clipvertex_and_position_outputs(shader, &clipvertex, &position))
	return false;

	/* insert CLIPDIST outputs */
	create_clipdist_vars(shader, out, ucp_enables, &maxloc, true);

	nir_builder_init(&b, impl);

	nir_foreach_block(block, impl)
	lower_clip_in_gs_block(&b, block, position, clipvertex, out, ucp_enables);

	nir_metadata_preserve(impl, nir_metadata_dominance);

	return true;
	}

	/*
	* FS lowering
	*/

	static void
	lower_clip_fs(nir_function_impl *impl, unsigned ucp_enables,
	nir_variable **in)
	{
	nir_ssa_def *clipdist[MAX_CLIP_PLANES];
	nir_builder b;

	nir_builder_init(&b, impl);
	b.cursor = nir_before_cf_list(&impl->body);

	if (ucp_enables & 0x0f)
	load_clipdist_input(&b, in[0], &clipdist[0]);
	if (ucp_enables & 0xf0)
	load_clipdist_input(&b, in[1], &clipdist[4]);

	for (int plane = 0; plane < MAX_CLIP_PLANES; plane++) {
	if (ucp_enables & (1 << plane)) {
	nir_intrinsic_instr *discard;
	nir_ssa_def *cond;

	cond = nir_flt(&b, clipdist[plane], nir_imm_float(&b, 0.0));

	discard = nir_intrinsic_instr_create(b.shader,
	nir_intrinsic_discard_if);
	discard->src[0] = nir_src_for_ssa(cond);
	nir_builder_instr_insert(&b, &discard->instr);

	b.shader->info.fs.uses_discard = true;
	}
	}

	nir_metadata_preserve(impl, nir_metadata_dominance);
	}

	/* insert conditional kill based on interpolated CLIPDIST
	*/
	bool
	nir_lower_clip_fs(nir_shader *shader, unsigned ucp_enables)
	{
	nir_variable *in[2];
	int maxloc = -1;

	if (!ucp_enables)
	return false;

	nir_foreach_variable(var, &shader->inputs) {
	int loc = var->data.driver_location;

	/* keep track of last used driver-location.. we'll be
	* appending CLIP_DIST0/CLIP_DIST1 after last existing
	* input:
	*/
	maxloc = MAX2(maxloc, loc);
	}

	/* The shader won't normally have CLIPDIST inputs, so we
	* must add our own:
	*/
	/* insert CLIPDIST inputs */
	create_clipdist_vars(shader, in, ucp_enables, &maxloc, false);

	nir_foreach_function(function, shader) {
	if (!strcmp(function->name, "main"))
	lower_clip_fs(function->impl, ucp_enables, in);
	}

	return true;
	}