intel/nir: Pass the nir_builder by reference in lower_alpha_to_coverage

[mesa.git] / src / intel / compiler / brw_nir_lower_image_load_store.c

/*
 * Copyright © 2018 Intel Corporation
 *
 * 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.
 */

#include "isl/isl.h"

#include "brw_nir.h"
#include "compiler/nir/nir_builder.h"
#include "compiler/nir/nir_format_convert.h"

static nir_ssa_def *
_load_image_param(nir_builder *b, nir_deref_instr *deref, unsigned offset)
{
   nir_intrinsic_instr *load =
      nir_intrinsic_instr_create(b->shader,
                                 nir_intrinsic_image_deref_load_param_intel);
   load->src[0] = nir_src_for_ssa(&deref->dest.ssa);
   nir_intrinsic_set_base(load, offset / 4);

   switch (offset) {
   case BRW_IMAGE_PARAM_OFFSET_OFFSET:
   case BRW_IMAGE_PARAM_SWIZZLING_OFFSET:
      load->num_components = 2;
      break;
   case BRW_IMAGE_PARAM_TILING_OFFSET:
   case BRW_IMAGE_PARAM_SIZE_OFFSET:
      load->num_components = 3;
      break;
   case BRW_IMAGE_PARAM_STRIDE_OFFSET:
      load->num_components = 4;
      break;
   default:
      unreachable("Invalid param offset");
   }
   nir_ssa_dest_init(&load->instr, &load->dest,
                     load->num_components, 32, NULL);

   nir_builder_instr_insert(b, &load->instr);
   return &load->dest.ssa;
}

#define load_image_param(b, d, o) \
   _load_image_param(b, d, BRW_IMAGE_PARAM_##o##_OFFSET)

static nir_ssa_def *
image_coord_is_in_bounds(nir_builder *b, nir_deref_instr *deref,
                         nir_ssa_def *coord)
{
   nir_ssa_def *size = load_image_param(b, deref, SIZE);
   nir_ssa_def *cmp = nir_ilt(b, coord, size);

   unsigned coord_comps = glsl_get_sampler_coordinate_components(deref->type);
   nir_ssa_def *in_bounds = nir_imm_true(b);
   for (unsigned i = 0; i < coord_comps; i++)
      in_bounds = nir_iand(b, in_bounds, nir_channel(b, cmp, i));

   return in_bounds;
}

/** Calculate the offset in memory of the texel given by \p coord.
 *
 * This is meant to be used with untyped surface messages to access a tiled
 * surface, what involves taking into account the tiling and swizzling modes
 * of the surface manually so it will hopefully not happen very often.
 *
 * The tiling algorithm implemented here matches either the X or Y tiling
 * layouts supported by the hardware depending on the tiling coefficients
 * passed to the program as uniforms.  See Volume 1 Part 2 Section 4.5
 * "Address Tiling Function" of the IVB PRM for an in-depth explanation of
 * the hardware tiling format.
 */
static nir_ssa_def *
image_address(nir_builder *b, const struct gen_device_info *devinfo,
              nir_deref_instr *deref, nir_ssa_def *coord)
{
   if (glsl_get_sampler_dim(deref->type) == GLSL_SAMPLER_DIM_1D &&
       glsl_sampler_type_is_array(deref->type)) {
      /* It's easier if 1D arrays are treated like 2D arrays */
      coord = nir_vec3(b, nir_channel(b, coord, 0),
                          nir_imm_int(b, 0),
                          nir_channel(b, coord, 1));
   } else {
      unsigned dims = glsl_get_sampler_coordinate_components(deref->type);
      coord = nir_channels(b, coord, (1 << dims) - 1);
   }

   nir_ssa_def *offset = load_image_param(b, deref, OFFSET);
   nir_ssa_def *tiling = load_image_param(b, deref, TILING);
   nir_ssa_def *stride = load_image_param(b, deref, STRIDE);

   /* Shift the coordinates by the fixed surface offset.  It may be non-zero
    * if the image is a single slice of a higher-dimensional surface, or if a
    * non-zero mipmap level of the surface is bound to the pipeline.  The
    * offset needs to be applied here rather than at surface state set-up time
    * because the desired slice-level may start mid-tile, so simply shifting
    * the surface base address wouldn't give a well-formed tiled surface in
    * the general case.
    */
   nir_ssa_def *xypos = (coord->num_components == 1) ?
                        nir_vec2(b, coord, nir_imm_int(b, 0)) :
                        nir_channels(b, coord, 0x3);
   xypos = nir_iadd(b, xypos, offset);

   /* The layout of 3-D textures in memory is sort-of like a tiling
    * format.  At each miplevel, the slices are arranged in rows of
    * 2^level slices per row.  The slice row is stored in tmp.y and
    * the slice within the row is stored in tmp.x.
    *
    * The layout of 2-D array textures and cubemaps is much simpler:
    * Depending on whether the ARYSPC_LOD0 layout is in use it will be
    * stored in memory as an array of slices, each one being a 2-D
    * arrangement of miplevels, or as a 2D arrangement of miplevels,
    * each one being an array of slices.  In either case the separation
    * between slices of the same LOD is equal to the qpitch value
    * provided as stride.w.
    *
    * This code can be made to handle either 2D arrays and 3D textures
    * by passing in the miplevel as tile.z for 3-D textures and 0 in
    * tile.z for 2-D array textures.
    *
    * See Volume 1 Part 1 of the Gen7 PRM, sections 6.18.4.7 "Surface
    * Arrays" and 6.18.6 "3D Surfaces" for a more extensive discussion
    * of the hardware 3D texture and 2D array layouts.
    */
   if (coord->num_components > 2) {
      /* Decompose z into a major (tmp.y) and a minor (tmp.x)
       * index.
       */
      nir_ssa_def *z = nir_channel(b, coord, 2);
      nir_ssa_def *z_x = nir_ubfe(b, z, nir_imm_int(b, 0),
                                  nir_channel(b, tiling, 2));
      nir_ssa_def *z_y = nir_ushr(b, z, nir_channel(b, tiling, 2));

      /* Take into account the horizontal (tmp.x) and vertical (tmp.y)
       * slice offset.
       */
      xypos = nir_iadd(b, xypos, nir_imul(b, nir_vec2(b, z_x, z_y),
                                             nir_channels(b, stride, 0xc)));
   }

   nir_ssa_def *addr;
   if (coord->num_components > 1) {
      /* Calculate the major/minor x and y indices.  In order to
       * accommodate both X and Y tiling, the Y-major tiling format is
       * treated as being a bunch of narrow X-tiles placed next to each
       * other.  This means that the tile width for Y-tiling is actually
       * the width of one sub-column of the Y-major tile where each 4K
       * tile has 8 512B sub-columns.
       *
       * The major Y value is the row of tiles in which the pixel lives.
       * The major X value is the tile sub-column in which the pixel
       * lives; for X tiling, this is the same as the tile column, for Y
       * tiling, each tile has 8 sub-columns.  The minor X and Y indices
       * are the position within the sub-column.
       */

      /* Calculate the minor x and y indices. */
      nir_ssa_def *minor = nir_ubfe(b, xypos, nir_imm_int(b, 0),
                                       nir_channels(b, tiling, 0x3));
      nir_ssa_def *major = nir_ushr(b, xypos, nir_channels(b, tiling, 0x3));

      /* Calculate the texel index from the start of the tile row and the
       * vertical coordinate of the row.
       * Equivalent to:
       *   tmp.x = (major.x << tile.y << tile.x) +
       *           (minor.y << tile.x) + minor.x
       *   tmp.y = major.y << tile.y
       */
      nir_ssa_def *idx_x, *idx_y;
      idx_x = nir_ishl(b, nir_channel(b, major, 0), nir_channel(b, tiling, 1));
      idx_x = nir_iadd(b, idx_x, nir_channel(b, minor, 1));
      idx_x = nir_ishl(b, idx_x, nir_channel(b, tiling, 0));
      idx_x = nir_iadd(b, idx_x, nir_channel(b, minor, 0));
      idx_y = nir_ishl(b, nir_channel(b, major, 1), nir_channel(b, tiling, 1));

      /* Add it to the start of the tile row. */
      nir_ssa_def *idx;
      idx = nir_imul(b, idx_y, nir_channel(b, stride, 1));
      idx = nir_iadd(b, idx, idx_x);

      /* Multiply by the Bpp value. */
      addr = nir_imul(b, idx, nir_channel(b, stride, 0));

      if (devinfo->gen < 8 && !devinfo->is_baytrail) {
         /* Take into account the two dynamically specified shifts.  Both are
          * used to implement swizzling of X-tiled surfaces.  For Y-tiled
          * surfaces only one bit needs to be XOR-ed with bit 6 of the memory
          * address, so a swz value of 0xff (actually interpreted as 31 by the
          * hardware) will be provided to cause the relevant bit of tmp.y to
          * be zero and turn the first XOR into the identity.  For linear
          * surfaces or platforms lacking address swizzling both shifts will
          * be 0xff causing the relevant bits of both tmp.x and .y to be zero,
          * what effectively disables swizzling.
          */
         nir_ssa_def *swizzle = load_image_param(b, deref, SWIZZLING);
         nir_ssa_def *shift0 = nir_ushr(b, addr, nir_channel(b, swizzle, 0));
         nir_ssa_def *shift1 = nir_ushr(b, addr, nir_channel(b, swizzle, 1));

         /* XOR tmp.x and tmp.y with bit 6 of the memory address. */
         nir_ssa_def *bit = nir_iand(b, nir_ixor(b, shift0, shift1),
                                        nir_imm_int(b, 1 << 6));
         addr = nir_ixor(b, addr, bit);
      }
   } else {
      /* Multiply by the Bpp/stride value.  Note that the addr.y may be
       * non-zero even if the image is one-dimensional because a vertical
       * offset may have been applied above to select a non-zero slice or
       * level of a higher-dimensional texture.
       */
      nir_ssa_def *idx;
      idx = nir_imul(b, nir_channel(b, xypos, 1), nir_channel(b, stride, 1));
      idx = nir_iadd(b, nir_channel(b, xypos, 0), idx);
      addr = nir_imul(b, idx, nir_channel(b, stride, 0));
   }

   return addr;
}

struct format_info {
   const struct isl_format_layout *fmtl;
   unsigned chans;
   unsigned bits[4];
};

static struct format_info
get_format_info(enum isl_format fmt)
{
   const struct isl_format_layout *fmtl = isl_format_get_layout(fmt);

   return (struct format_info) {
      .fmtl = fmtl,
      .chans = isl_format_get_num_channels(fmt),
      .bits = {
         fmtl->channels.r.bits,
         fmtl->channels.g.bits,
         fmtl->channels.b.bits,
         fmtl->channels.a.bits
      },
   };
}

static nir_ssa_def *
convert_color_for_load(nir_builder *b, const struct gen_device_info *devinfo,
                       nir_ssa_def *color,
                       enum isl_format image_fmt, enum isl_format lower_fmt,
                       unsigned dest_components)
{
   if (image_fmt == lower_fmt)
      goto expand_vec;

   if (image_fmt == ISL_FORMAT_R11G11B10_FLOAT) {
      assert(lower_fmt == ISL_FORMAT_R32_UINT);
      color = nir_format_unpack_11f11f10f(b, color);
      goto expand_vec;
   }

   struct format_info image = get_format_info(image_fmt);
   struct format_info lower = get_format_info(lower_fmt);

   const bool needs_sign_extension =
      isl_format_has_snorm_channel(image_fmt) ||
      isl_format_has_sint_channel(image_fmt);

   /* We only check the red channel to detect if we need to pack/unpack */
   assert(image.bits[0] != lower.bits[0] ||
          memcmp(image.bits, lower.bits, sizeof(image.bits)) == 0);

   if (image.bits[0] != lower.bits[0] && lower_fmt == ISL_FORMAT_R32_UINT) {
      if (needs_sign_extension)
         color = nir_format_unpack_sint(b, color, image.bits, image.chans);
      else
         color = nir_format_unpack_uint(b, color, image.bits, image.chans);
   } else {
      /* All these formats are homogeneous */
      for (unsigned i = 1; i < image.chans; i++)
         assert(image.bits[i] == image.bits[0]);

      /* On IVB, we rely on the undocumented behavior that typed reads from
       * surfaces of the unsupported R8 and R16 formats return useful data in
       * their least significant bits.  However, the data in the high bits is
       * garbage so we have to discard it.
       */
      if (devinfo->gen == 7 && !devinfo->is_haswell &&
          (lower_fmt == ISL_FORMAT_R16_UINT ||
           lower_fmt == ISL_FORMAT_R8_UINT))
         color = nir_format_mask_uvec(b, color, lower.bits);

      if (image.bits[0] != lower.bits[0]) {
         color = nir_format_bitcast_uvec_unmasked(b, color, lower.bits[0],
                                                  image.bits[0]);
      }

      if (needs_sign_extension)
         color = nir_format_sign_extend_ivec(b, color, image.bits);
   }

   switch (image.fmtl->channels.r.type) {
   case ISL_UNORM:
      assert(isl_format_has_uint_channel(lower_fmt));
      color = nir_format_unorm_to_float(b, color, image.bits);
      break;

   case ISL_SNORM:
      assert(isl_format_has_uint_channel(lower_fmt));
      color = nir_format_snorm_to_float(b, color, image.bits);
      break;

   case ISL_SFLOAT:
      if (image.bits[0] == 16)
         color = nir_unpack_half_2x16_split_x(b, color);
      break;

   case ISL_UINT:
   case ISL_SINT:
      break;

   default:
      unreachable("Invalid image channel type");
   }

expand_vec:
   assert(dest_components == 1 || dest_components == 4);
   assert(color->num_components <= dest_components);
   if (color->num_components == dest_components)
      return color;

   nir_ssa_def *comps[4];
   for (unsigned i = 0; i < color->num_components; i++)
      comps[i] = nir_channel(b, color, i);

   for (unsigned i = color->num_components; i < 3; i++)
      comps[i] = nir_imm_int(b, 0);

   if (color->num_components < 4) {
      if (isl_format_has_int_channel(image_fmt))
         comps[3] = nir_imm_int(b, 1);
      else
         comps[3] = nir_imm_float(b, 1);
   }

   return nir_vec(b, comps, dest_components);
}

static bool
lower_image_load_instr(nir_builder *b,
                       const struct gen_device_info *devinfo,
                       nir_intrinsic_instr *intrin)
{
   nir_deref_instr *deref = nir_src_as_deref(intrin->src[0]);
   nir_variable *var = nir_deref_instr_get_variable(deref);
   const enum isl_format image_fmt =
      isl_format_for_pipe_format(var->data.image.format);

   if (isl_has_matching_typed_storage_image_format(devinfo, image_fmt)) {
      const enum isl_format lower_fmt =
         isl_lower_storage_image_format(devinfo, image_fmt);
      const unsigned dest_components = intrin->num_components;

      /* Use an undef to hold the uses of the load while we do the color
       * conversion.
       */
      nir_ssa_def *placeholder = nir_ssa_undef(b, 4, 32);
      nir_ssa_def_rewrite_uses(&intrin->dest.ssa, nir_src_for_ssa(placeholder));

      intrin->num_components = isl_format_get_num_channels(lower_fmt);
      intrin->dest.ssa.num_components = intrin->num_components;

      b->cursor = nir_after_instr(&intrin->instr);

      nir_ssa_def *color = convert_color_for_load(b, devinfo,
                                                  &intrin->dest.ssa,
                                                  image_fmt, lower_fmt,
                                                  dest_components);

      nir_ssa_def_rewrite_uses(placeholder, nir_src_for_ssa(color));
      nir_instr_remove(placeholder->parent_instr);
   } else {
      const struct isl_format_layout *image_fmtl =
         isl_format_get_layout(image_fmt);
      /* We have a matching typed format for everything 32b and below */
      assert(image_fmtl->bpb == 64 || image_fmtl->bpb == 128);
      enum isl_format raw_fmt = (image_fmtl->bpb == 64) ?
                                ISL_FORMAT_R32G32_UINT :
                                ISL_FORMAT_R32G32B32A32_UINT;
      const unsigned dest_components = intrin->num_components;

      b->cursor = nir_instr_remove(&intrin->instr);

      nir_ssa_def *coord = intrin->src[1].ssa;

      nir_ssa_def *do_load = image_coord_is_in_bounds(b, deref, coord);
      if (devinfo->gen == 7 && !devinfo->is_haswell) {
         /* Check whether the first stride component (i.e. the Bpp value)
          * is greater than four, what on Gen7 indicates that a surface of
          * type RAW has been bound for untyped access.  Reading or writing
          * to a surface of type other than RAW using untyped surface
          * messages causes a hang on IVB and VLV.
          */
         nir_ssa_def *stride = load_image_param(b, deref, STRIDE);
         nir_ssa_def *is_raw =
            nir_ilt(b, nir_imm_int(b, 4), nir_channel(b, stride, 0));
         do_load = nir_iand(b, do_load, is_raw);
      }
      nir_push_if(b, do_load);

      nir_ssa_def *addr = image_address(b, devinfo, deref, coord);
      nir_intrinsic_instr *load =
         nir_intrinsic_instr_create(b->shader,
                                    nir_intrinsic_image_deref_load_raw_intel);
      load->src[0] = nir_src_for_ssa(&deref->dest.ssa);
      load->src[1] = nir_src_for_ssa(addr);
      load->num_components = image_fmtl->bpb / 32;
      nir_ssa_dest_init(&load->instr, &load->dest,
                        load->num_components, 32, NULL);
      nir_builder_instr_insert(b, &load->instr);

      nir_push_else(b, NULL);

      nir_ssa_def *zero = nir_imm_zero(b, load->num_components, 32);

      nir_pop_if(b, NULL);

      nir_ssa_def *value = nir_if_phi(b, &load->dest.ssa, zero);

      nir_ssa_def *color = convert_color_for_load(b, devinfo, value,
                                                  image_fmt, raw_fmt,
                                                  dest_components);

      nir_ssa_def_rewrite_uses(&intrin->dest.ssa, nir_src_for_ssa(color));
   }

   return true;
}

static nir_ssa_def *
convert_color_for_store(nir_builder *b, const struct gen_device_info *devinfo,
                        nir_ssa_def *color,
                        enum isl_format image_fmt, enum isl_format lower_fmt)
{
   struct format_info image = get_format_info(image_fmt);
   struct format_info lower = get_format_info(lower_fmt);

   color = nir_channels(b, color, (1 << image.chans) - 1);

   if (image_fmt == lower_fmt)
      return color;

   if (image_fmt == ISL_FORMAT_R11G11B10_FLOAT) {
      assert(lower_fmt == ISL_FORMAT_R32_UINT);
      return nir_format_pack_11f11f10f(b, color);
   }

   switch (image.fmtl->channels.r.type) {
   case ISL_UNORM:
      assert(isl_format_has_uint_channel(lower_fmt));
      color = nir_format_float_to_unorm(b, color, image.bits);
      break;

   case ISL_SNORM:
      assert(isl_format_has_uint_channel(lower_fmt));
      color = nir_format_float_to_snorm(b, color, image.bits);
      break;

   case ISL_SFLOAT:
      if (image.bits[0] == 16)
         color = nir_format_float_to_half(b, color);
      break;

   case ISL_UINT:
      color = nir_format_clamp_uint(b, color, image.bits);
      break;

   case ISL_SINT:
      color = nir_format_clamp_sint(b, color, image.bits);
      break;

   default:
      unreachable("Invalid image channel type");
   }

   if (image.bits[0] < 32 &&
       (isl_format_has_snorm_channel(image_fmt) ||
        isl_format_has_sint_channel(image_fmt)))
      color = nir_format_mask_uvec(b, color, image.bits);

   if (image.bits[0] != lower.bits[0] && lower_fmt == ISL_FORMAT_R32_UINT) {
      color = nir_format_pack_uint(b, color, image.bits, image.chans);
   } else {
      /* All these formats are homogeneous */
      for (unsigned i = 1; i < image.chans; i++)
         assert(image.bits[i] == image.bits[0]);

      if (image.bits[0] != lower.bits[0]) {
         color = nir_format_bitcast_uvec_unmasked(b, color, image.bits[0],
                                                  lower.bits[0]);
      }
   }

   return color;
}

static bool
lower_image_store_instr(nir_builder *b,
                        const struct gen_device_info *devinfo,
                        nir_intrinsic_instr *intrin)
{
   nir_deref_instr *deref = nir_src_as_deref(intrin->src[0]);
   nir_variable *var = nir_deref_instr_get_variable(deref);

   /* For write-only surfaces, we trust that the hardware can just do the
    * conversion for us.
    */
   if (var->data.access & ACCESS_NON_READABLE)
      return false;

   const enum isl_format image_fmt =
      isl_format_for_pipe_format(var->data.image.format);

   if (isl_has_matching_typed_storage_image_format(devinfo, image_fmt)) {
      const enum isl_format lower_fmt =
         isl_lower_storage_image_format(devinfo, image_fmt);

      /* Color conversion goes before the store */
      b->cursor = nir_before_instr(&intrin->instr);

      nir_ssa_def *color = convert_color_for_store(b, devinfo,
                                                   intrin->src[3].ssa,
                                                   image_fmt, lower_fmt);
      intrin->num_components = isl_format_get_num_channels(lower_fmt);
      nir_instr_rewrite_src(&intrin->instr, &intrin->src[3],
                            nir_src_for_ssa(color));
   } else {
      const struct isl_format_layout *image_fmtl =
         isl_format_get_layout(image_fmt);
      /* We have a matching typed format for everything 32b and below */
      assert(image_fmtl->bpb == 64 || image_fmtl->bpb == 128);
      enum isl_format raw_fmt = (image_fmtl->bpb == 64) ?
                                ISL_FORMAT_R32G32_UINT :
                                ISL_FORMAT_R32G32B32A32_UINT;

      b->cursor = nir_instr_remove(&intrin->instr);

      nir_ssa_def *coord = intrin->src[1].ssa;

      nir_ssa_def *do_store = image_coord_is_in_bounds(b, deref, coord);
      if (devinfo->gen == 7 && !devinfo->is_haswell) {
         /* Check whether the first stride component (i.e. the Bpp value)
          * is greater than four, what on Gen7 indicates that a surface of
          * type RAW has been bound for untyped access.  Reading or writing
          * to a surface of type other than RAW using untyped surface
          * messages causes a hang on IVB and VLV.
          */
         nir_ssa_def *stride = load_image_param(b, deref, STRIDE);
         nir_ssa_def *is_raw =
            nir_ilt(b, nir_imm_int(b, 4), nir_channel(b, stride, 0));
         do_store = nir_iand(b, do_store, is_raw);
      }
      nir_push_if(b, do_store);

      nir_ssa_def *addr = image_address(b, devinfo, deref, coord);
      nir_ssa_def *color = convert_color_for_store(b, devinfo,
                                                   intrin->src[3].ssa,
                                                   image_fmt, raw_fmt);

      nir_intrinsic_instr *store =
         nir_intrinsic_instr_create(b->shader,
                                    nir_intrinsic_image_deref_store_raw_intel);
      store->src[0] = nir_src_for_ssa(&deref->dest.ssa);
      store->src[1] = nir_src_for_ssa(addr);
      store->src[2] = nir_src_for_ssa(color);
      store->num_components = image_fmtl->bpb / 32;
      nir_builder_instr_insert(b, &store->instr);

      nir_pop_if(b, NULL);
   }

   return true;
}

static bool
lower_image_atomic_instr(nir_builder *b,
                         const struct gen_device_info *devinfo,
                         nir_intrinsic_instr *intrin)
{
   if (devinfo->is_haswell || devinfo->gen >= 8)
      return false;

   nir_deref_instr *deref = nir_src_as_deref(intrin->src[0]);

   b->cursor = nir_instr_remove(&intrin->instr);

   /* Use an undef to hold the uses of the load conversion. */
   nir_ssa_def *placeholder = nir_ssa_undef(b, 4, 32);
   nir_ssa_def_rewrite_uses(&intrin->dest.ssa, nir_src_for_ssa(placeholder));

   /* Check the first component of the size field to find out if the
    * image is bound.  Necessary on IVB for typed atomics because
    * they don't seem to respect null surfaces and will happily
    * corrupt or read random memory when no image is bound.
    */
   nir_ssa_def *size = load_image_param(b, deref, SIZE);
   nir_ssa_def *zero = nir_imm_int(b, 0);
   nir_push_if(b, nir_ine(b, nir_channel(b, size, 0), zero));

   nir_builder_instr_insert(b, &intrin->instr);

   nir_pop_if(b, NULL);

   nir_ssa_def *result = nir_if_phi(b, &intrin->dest.ssa, zero);
   nir_ssa_def_rewrite_uses(placeholder, nir_src_for_ssa(result));

   return true;
}

static bool
lower_image_size_instr(nir_builder *b,
                       const struct gen_device_info *devinfo,
                       nir_intrinsic_instr *intrin)
{
   nir_deref_instr *deref = nir_src_as_deref(intrin->src[0]);
   nir_variable *var = nir_deref_instr_get_variable(deref);

   /* For write-only images, we have an actual image surface so we fall back
    * and let the back-end emit a TXS for this.
    */
   if (var->data.access & ACCESS_NON_READABLE)
      return false;

   /* If we have a matching typed format, then we have an actual image surface
    * so we fall back and let the back-end emit a TXS for this.
    */
   const enum isl_format image_fmt =
      isl_format_for_pipe_format(var->data.image.format);
   if (isl_has_matching_typed_storage_image_format(devinfo, image_fmt))
      return false;

   assert(nir_src_as_uint(intrin->src[1]) == 0);

   b->cursor = nir_instr_remove(&intrin->instr);

   nir_ssa_def *size = load_image_param(b, deref, SIZE);

   nir_ssa_def *comps[4] = { NULL, NULL, NULL, NULL };

   enum glsl_sampler_dim dim = glsl_get_sampler_dim(deref->type);
   unsigned coord_comps = glsl_get_sampler_coordinate_components(deref->type);
   for (unsigned c = 0; c < coord_comps; c++) {
      if (c == 2 && dim == GLSL_SAMPLER_DIM_CUBE) {
         comps[2] = nir_idiv(b, nir_channel(b, size, 2), nir_imm_int(b, 6));
      } else {
         comps[c] = nir_channel(b, size, c);
      }
   }

   for (unsigned c = coord_comps; c < intrin->dest.ssa.num_components; ++c)
      comps[c] = nir_imm_int(b, 1);

   nir_ssa_def *vec = nir_vec(b, comps, intrin->dest.ssa.num_components);
   nir_ssa_def_rewrite_uses(&intrin->dest.ssa, nir_src_for_ssa(vec));

   return true;
}

bool
brw_nir_lower_image_load_store(nir_shader *shader,
                               const struct gen_device_info *devinfo,
                               bool *uses_atomic_load_store)
{
   bool progress = false;

   nir_foreach_function(function, shader) {
      if (function->impl == NULL)
         continue;

      bool impl_progress = false;
      nir_foreach_block_safe(block, function->impl) {
         nir_builder b;
         nir_builder_init(&b, function->impl);

         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_image_deref_load:
               if (lower_image_load_instr(&b, devinfo, intrin))
                  impl_progress = true;
               break;

            case nir_intrinsic_image_deref_store:
               if (lower_image_store_instr(&b, devinfo, intrin))
                  impl_progress = true;
               break;

            case nir_intrinsic_image_deref_atomic_add:
            case nir_intrinsic_image_deref_atomic_imin:
            case nir_intrinsic_image_deref_atomic_umin:
            case nir_intrinsic_image_deref_atomic_imax:
            case nir_intrinsic_image_deref_atomic_umax:
            case nir_intrinsic_image_deref_atomic_and:
            case nir_intrinsic_image_deref_atomic_or:
            case nir_intrinsic_image_deref_atomic_xor:
            case nir_intrinsic_image_deref_atomic_exchange:
            case nir_intrinsic_image_deref_atomic_comp_swap:
               if (uses_atomic_load_store)
                  *uses_atomic_load_store = true;
               if (lower_image_atomic_instr(&b, devinfo, intrin))
                  impl_progress = true;
               break;

            case nir_intrinsic_image_deref_size:
               if (lower_image_size_instr(&b, devinfo, intrin))
                  impl_progress = true;
               break;

            default:
               /* Nothing to do */
               break;
            }
         }
      }

      if (impl_progress) {
         progress = true;
         nir_metadata_preserve(function->impl, nir_metadata_none);
      } else {
         nir_metadata_preserve(function->impl, nir_metadata_all);
      }
   }

   return progress;
}