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IABSD.fr/xenocara/lib/mesa/src/intel/compiler/brw_lower_subgroup_ops.cpp

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  • Author : jsg
    Date : 2025-06-05 11:23:11
    Hash : 67d6f117
    Message : Import Mesa 25.0.7

  • lib/mesa/src/intel/compiler/brw_lower_subgroup_ops.cpp
  • /*
     * Copyright 2024 Intel Corporation
     * SPDX-License-Identifier: MIT
     */
    
    #include <stdint.h>
    #include "util/half_float.h"
    
    #include "brw_fs.h"
    #include "brw_builder.h"
    
    using namespace brw;
    
    struct brw_reduction_info {
       brw_reg             identity;
       enum opcode         op;
       brw_conditional_mod cond_mod;
    };
    
    static brw_reduction_info
    brw_get_reduction_info(brw_reduce_op red_op, brw_reg_type type)
    {
       struct brw_reduction_info info;
    
       info.op = BRW_OPCODE_SEL;
       info.cond_mod = BRW_CONDITIONAL_NONE;
    
       switch (red_op) {
       case BRW_REDUCE_OP_ADD: info.op = BRW_OPCODE_ADD;           break;
       case BRW_REDUCE_OP_MUL: info.op = BRW_OPCODE_MUL;           break;
       case BRW_REDUCE_OP_AND: info.op = BRW_OPCODE_AND;           break;
       case BRW_REDUCE_OP_OR:  info.op = BRW_OPCODE_OR;            break;
       case BRW_REDUCE_OP_XOR: info.op = BRW_OPCODE_XOR;           break;
       case BRW_REDUCE_OP_MIN: info.cond_mod = BRW_CONDITIONAL_L;  break;
       case BRW_REDUCE_OP_MAX: info.cond_mod = BRW_CONDITIONAL_GE; break;
       default:
          unreachable("invalid reduce op");
       }
    
       switch (red_op) {
       case BRW_REDUCE_OP_ADD:
       case BRW_REDUCE_OP_XOR:
       case BRW_REDUCE_OP_OR:
          info.identity = retype(brw_imm_u64(0), type);
          return info;
       case BRW_REDUCE_OP_AND:
          info.identity = retype(brw_imm_u64(~0ull), type);
          return info;
       default:
          /* Continue below. */
          break;
       }
    
       brw_reg id;
       const unsigned size = brw_type_size_bytes(type);
    
       switch (red_op) {
       case BRW_REDUCE_OP_MUL: {
          if (brw_type_is_int(type)) {
             id = size < 4  ? brw_imm_uw(1) :
                  size == 4 ? brw_imm_ud(1) :
                              brw_imm_u64(1);
          } else {
             assert(brw_type_is_float(type));
             id = size == 2 ? brw_imm_uw(_mesa_float_to_half(1.0)) :
                  size == 4 ? brw_imm_f(1.0) :
                              brw_imm_df(1.0);
          }
          break;
       }
    
       case BRW_REDUCE_OP_MIN: {
          if (brw_type_is_uint(type)) {
             id = brw_imm_u64(~0ull);
          } else if (brw_type_is_sint(type)) {
             id = size == 1 ? brw_imm_w(INT8_MAX) :
                  size == 2 ? brw_imm_w(INT16_MAX) :
                  size == 4 ? brw_imm_d(INT32_MAX) :
                              brw_imm_q(INT64_MAX);
          } else {
             assert(brw_type_is_float(type));
             id = size == 2 ? brw_imm_uw(_mesa_float_to_half(INFINITY)) :
                  size == 4 ? brw_imm_f(INFINITY) :
                              brw_imm_df(INFINITY);
          }
          break;
       }
    
       case BRW_REDUCE_OP_MAX: {
          if (brw_type_is_uint(type)) {
             id = brw_imm_u64(0);
          } else if (brw_type_is_sint(type)) {
             id = size == 1 ? brw_imm_w(INT8_MIN) :
                  size == 2 ? brw_imm_w(INT16_MIN) :
                  size == 4 ? brw_imm_d(INT32_MIN) :
                              brw_imm_q(INT64_MIN);
          } else {
             assert(brw_type_is_float(type));
             id = size == 2 ? brw_imm_uw(_mesa_float_to_half(-INFINITY)) :
                  size == 4 ? brw_imm_f(-INFINITY) :
                              brw_imm_df(-INFINITY);
          }
          break;
       }
    
       default:
          unreachable("invalid reduce op");
       }
    
       /* For some cases above (e.g. all bits zeros, all bits ones, first bit one)
        * either the size or the signedness was ignored, so adjust the final type
        * now.
        *
        * B/UB types can't have immediates, so used W/UW above and here.
        */
       if      (type == BRW_TYPE_UB) type = BRW_TYPE_UW;
       else if (type == BRW_TYPE_B)  type = BRW_TYPE_W;
    
       info.identity = retype(id, type);
    
       return info;
    }
    
    static void
    brw_emit_scan_step(const brw_builder &bld, enum opcode opcode, brw_conditional_mod mod,
                       const brw_reg &tmp,
                       unsigned left_offset, unsigned left_stride,
                       unsigned right_offset, unsigned right_stride)
    {
       brw_reg left, right;
       left = horiz_stride(horiz_offset(tmp, left_offset), left_stride);
       right = horiz_stride(horiz_offset(tmp, right_offset), right_stride);
       if ((tmp.type == BRW_TYPE_Q || tmp.type == BRW_TYPE_UQ) &&
           (!bld.shader->devinfo->has_64bit_int || bld.shader->devinfo->ver >= 20)) {
          switch (opcode) {
          case BRW_OPCODE_MUL:
             /* This will get lowered by integer MUL lowering */
             set_condmod(mod, bld.emit(opcode, right, left, right));
             break;
    
          case BRW_OPCODE_SEL: {
             /* In order for the comparisons to work out right, we need our
              * comparisons to be strict.
              */
             assert(mod == BRW_CONDITIONAL_L || mod == BRW_CONDITIONAL_GE);
             if (mod == BRW_CONDITIONAL_GE)
                mod = BRW_CONDITIONAL_G;
    
             /* We treat the bottom 32 bits as unsigned regardless of
              * whether or not the integer as a whole is signed.
              */
             brw_reg right_low = subscript(right, BRW_TYPE_UD, 0);
             brw_reg left_low = subscript(left, BRW_TYPE_UD, 0);
    
             /* The upper bits get the same sign as the 64-bit type */
             brw_reg_type type32 = brw_type_with_size(tmp.type, 32);
             brw_reg right_high = subscript(right, type32, 1);
             brw_reg left_high = subscript(left, type32, 1);
    
             /* Build up our comparison:
              *
              *   l_hi < r_hi || (l_hi == r_hi && l_low < r_low)
              */
             bld.CMP(bld.null_reg_ud(), retype(left_low, BRW_TYPE_UD),
                                retype(right_low, BRW_TYPE_UD), mod);
             set_predicate(BRW_PREDICATE_NORMAL,
                           bld.CMP(bld.null_reg_ud(), left_high, right_high,
                               BRW_CONDITIONAL_EQ));
             set_predicate_inv(BRW_PREDICATE_NORMAL, true,
                               bld.CMP(bld.null_reg_ud(), left_high, right_high, mod));
    
             /* We could use selects here or we could use predicated MOVs
              * because the destination and second source (if it were a SEL)
              * are the same.
              */
             set_predicate(BRW_PREDICATE_NORMAL, bld.MOV(right_low, left_low));
             set_predicate(BRW_PREDICATE_NORMAL, bld.MOV(right_high, left_high));
             break;
          }
    
          default:
             unreachable("Unsupported 64-bit scan op");
          }
       } else {
          set_condmod(mod, bld.emit(opcode, right, left, right));
       }
    }
    
    static void
    brw_emit_scan(const brw_builder &bld, enum opcode opcode, const brw_reg &tmp,
                  unsigned cluster_size, brw_conditional_mod mod)
    {
       unsigned dispatch_width = bld.dispatch_width();
       assert(dispatch_width >= 8);
    
       /* The instruction splitting code isn't advanced enough to split
        * these so we need to handle that ourselves.
        */
       if (dispatch_width * brw_type_size_bytes(tmp.type) > 2 * REG_SIZE) {
          const unsigned half_width = dispatch_width / 2;
          const brw_builder ubld = bld.exec_all().group(half_width, 0);
          brw_reg left = tmp;
          brw_reg right = horiz_offset(tmp, half_width);
          brw_emit_scan(ubld, opcode, left, cluster_size, mod);
          brw_emit_scan(ubld, opcode, right, cluster_size, mod);
          if (cluster_size > half_width) {
             brw_emit_scan_step(ubld, opcode, mod, tmp,
                                half_width - 1, 0, half_width, 1);
          }
          return;
       }
    
       if (cluster_size > 1) {
          const brw_builder ubld = bld.exec_all().group(dispatch_width / 2, 0);
          brw_emit_scan_step(ubld, opcode, mod, tmp, 0, 2, 1, 2);
       }
    
       if (cluster_size > 2) {
          if (brw_type_size_bytes(tmp.type) <= 4) {
             const brw_builder ubld =
                bld.exec_all().group(dispatch_width / 4, 0);
             brw_emit_scan_step(ubld, opcode, mod, tmp, 1, 4, 2, 4);
             brw_emit_scan_step(ubld, opcode, mod, tmp, 1, 4, 3, 4);
          } else {
             /* For 64-bit types, we have to do things differently because
              * the code above would land us with destination strides that
              * the hardware can't handle.  Fortunately, we'll only be
              * 8-wide in that case and it's the same number of
              * instructions.
              */
             const brw_builder ubld = bld.exec_all().group(2, 0);
             for (unsigned i = 0; i < dispatch_width; i += 4)
                brw_emit_scan_step(ubld, opcode, mod, tmp, i + 1, 0, i + 2, 1);
          }
       }
    
       for (unsigned i = 4;
            i < MIN2(cluster_size, dispatch_width);
            i *= 2) {
          const brw_builder ubld = bld.exec_all().group(i, 0);
          brw_emit_scan_step(ubld, opcode, mod, tmp, i - 1, 0, i, 1);
    
          if (dispatch_width > i * 2)
             brw_emit_scan_step(ubld, opcode, mod, tmp, i * 3 - 1, 0, i * 3, 1);
    
          if (dispatch_width > i * 4) {
             brw_emit_scan_step(ubld, opcode, mod, tmp, i * 5 - 1, 0, i * 5, 1);
             brw_emit_scan_step(ubld, opcode, mod, tmp, i * 7 - 1, 0, i * 7, 1);
          }
       }
    }
    
    static bool
    brw_lower_reduce(fs_visitor &s, bblock_t *block, fs_inst *inst)
    {
       const brw_builder bld(&s, block, inst);
    
       assert(inst->dst.type == inst->src[0].type);
       brw_reg dst = inst->dst;
       brw_reg src = inst->src[0];
    
       assert(inst->src[1].file == IMM);
       enum brw_reduce_op op = (enum brw_reduce_op)inst->src[1].ud;
    
       assert(inst->src[2].file == IMM);
       unsigned cluster_size = inst->src[2].ud;
    
       assert(cluster_size > 0);
       assert(cluster_size <= s.dispatch_width);
    
       struct brw_reduction_info info = brw_get_reduction_info(op, src.type);
    
       /* Set up a register for all of our scratching around and initialize it
        * to reduction operation's identity value.
        */
       brw_reg scan = bld.vgrf(src.type);
       bld.exec_all().emit(SHADER_OPCODE_SEL_EXEC, scan, src, info.identity);
    
       brw_emit_scan(bld, info.op, scan, cluster_size, info.cond_mod);
    
       if (cluster_size * brw_type_size_bytes(src.type) >= REG_SIZE * 2) {
          /* In this case, CLUSTER_BROADCAST instruction isn't needed because
           * the distance between clusters is at least 2 GRFs.  In this case,
           * we don't need the weird striding of the CLUSTER_BROADCAST
           * instruction and can just do regular MOVs.
           */
          assert((cluster_size * brw_type_size_bytes(src.type)) % (REG_SIZE * 2) == 0);
          const unsigned groups =
             (s.dispatch_width * brw_type_size_bytes(src.type)) / (REG_SIZE * 2);
          const unsigned group_size = s.dispatch_width / groups;
          for (unsigned i = 0; i < groups; i++) {
             const unsigned cluster = (i * group_size) / cluster_size;
             const unsigned comp = cluster * cluster_size + (cluster_size - 1);
             bld.group(group_size, i).MOV(horiz_offset(dst, i * group_size),
                                          component(scan, comp));
          }
       } else {
          bld.emit(SHADER_OPCODE_CLUSTER_BROADCAST, dst, scan,
                   brw_imm_ud(cluster_size - 1), brw_imm_ud(cluster_size));
       }
       inst->remove(block);
       return true;
    }
    
    static bool
    brw_lower_scan(fs_visitor &s, bblock_t *block, fs_inst *inst)
    {
       const brw_builder bld(&s, block, inst);
    
       assert(inst->dst.type == inst->src[0].type);
       brw_reg dst = inst->dst;
       brw_reg src = inst->src[0];
    
       assert(inst->src[1].file == IMM);
       enum brw_reduce_op op = (enum brw_reduce_op)inst->src[1].ud;
    
       struct brw_reduction_info info = brw_get_reduction_info(op, src.type);
    
       /* Set up a register for all of our scratching around and initialize it
        * to reduction operation's identity value.
        */
       brw_reg scan = bld.vgrf(src.type);
       const brw_builder ubld = bld.exec_all();
       ubld.emit(SHADER_OPCODE_SEL_EXEC, scan, src, info.identity);
    
       if (inst->opcode == SHADER_OPCODE_EXCLUSIVE_SCAN) {
          /* Exclusive scan is a bit harder because we have to do an annoying
           * shift of the contents before we can begin.  To make things worse,
           * we can't do this with a normal stride; we have to use indirects.
           */
          brw_reg shifted = bld.vgrf(src.type);
          brw_reg idx = bld.vgrf(BRW_TYPE_UW);
    
          /* Set the saturate modifier in the offset index to ensure it's
           * normalized within the expected range without negative values,
           * since the situation can cause us to read past the end of the
           * register file leading to hangs on Xe3.
           */
          set_saturate(true, ubld.ADD(idx, bld.LOAD_SUBGROUP_INVOCATION(),
                                      brw_imm_w(-1)));
          ubld.emit(SHADER_OPCODE_SHUFFLE, shifted, scan, idx);
          ubld.group(1, 0).MOV(horiz_offset(shifted, 0), info.identity);
          scan = shifted;
       }
    
       brw_emit_scan(bld, info.op, scan, s.dispatch_width, info.cond_mod);
    
       bld.MOV(dst, scan);
    
       inst->remove(block);
       return true;
    }
    
    static brw_reg
    brw_fill_flag(const brw_builder &bld, unsigned v)
    {
       const brw_builder ubld1 = bld.exec_all().group(1, 0);
       brw_reg flag = brw_flag_reg(0, 0);
    
       if (bld.shader->dispatch_width == 32) {
          /* For SIMD32, we use a UD type so we fill both f0.0 and f0.1. */
          flag = retype(flag, BRW_TYPE_UD);
          ubld1.MOV(flag, brw_imm_ud(v));
       } else {
          ubld1.MOV(flag, brw_imm_uw(v & 0xFFFF));
       }
    
       return flag;
    }
    
    static void
    brw_lower_dispatch_width_vote(const brw_builder &bld, enum opcode opcode, brw_reg dst, brw_reg src)
    {
       const intel_device_info *devinfo = bld.shader->devinfo;
       const unsigned dispatch_width = bld.shader->dispatch_width;
    
       assert(opcode == SHADER_OPCODE_VOTE_ANY ||
              opcode == SHADER_OPCODE_VOTE_ALL ||
              opcode == SHADER_OPCODE_VOTE_EQUAL);
    
       const bool any   = opcode == SHADER_OPCODE_VOTE_ANY;
       const bool equal = opcode == SHADER_OPCODE_VOTE_EQUAL;
    
       const brw_reg ref = equal ? bld.emit_uniformize(src) : brw_imm_d(0);
    
       /* The any/all predicates do not consider channel enables. To prevent
        * dead channels from affecting the result, we initialize the flag with
        * with the identity value for the logical operation.
        */
       brw_fill_flag(bld, any ? 0 : 0xFFFFFFFF);
       bld.CMP(bld.null_reg_d(), src, ref, equal ? BRW_CONDITIONAL_Z
                                                 : BRW_CONDITIONAL_NZ);
    
       /* For some reason, the any/all predicates don't work properly with
        * SIMD32.  In particular, it appears that a SEL with a QtrCtrl of 2H
        * doesn't read the correct subset of the flag register and you end up
        * getting garbage in the second half.  Work around this by using a pair
        * of 1-wide MOVs and scattering the result.
        *
        * TODO: Check if we still need this for newer platforms.
        */
       const brw_builder ubld = devinfo->ver >= 20 ? bld.exec_all()
                                                   : bld.exec_all().group(1, 0);
       brw_reg res1 = ubld.MOV(brw_imm_d(0));
    
       enum brw_predicate pred;
       if (any) {
          pred = devinfo->ver >= 20   ? XE2_PREDICATE_ANY :
                 dispatch_width == 8  ? BRW_PREDICATE_ALIGN1_ANY8H :
                 dispatch_width == 16 ? BRW_PREDICATE_ALIGN1_ANY16H :
                                        BRW_PREDICATE_ALIGN1_ANY32H;
       } else {
          pred = devinfo->ver >= 20   ? XE2_PREDICATE_ALL :
                 dispatch_width == 8  ? BRW_PREDICATE_ALIGN1_ALL8H :
                 dispatch_width == 16 ? BRW_PREDICATE_ALIGN1_ALL16H :
                                        BRW_PREDICATE_ALIGN1_ALL32H;
       }
       set_predicate(pred, ubld.MOV(res1, brw_imm_d(-1)));
    
       bld.MOV(retype(dst, BRW_TYPE_D), component(res1, 0));
    }
    
    static void
    brw_lower_quad_vote_gfx9(const brw_builder &bld, enum opcode opcode, brw_reg dst, brw_reg src)
    {
       assert(opcode == SHADER_OPCODE_VOTE_ANY || opcode == SHADER_OPCODE_VOTE_ALL);
       const bool any = opcode == SHADER_OPCODE_VOTE_ANY;
    
       /* The any/all predicates do not consider channel enables. To prevent
        * dead channels from affecting the result, we initialize the flag with
        * with the identity value for the logical operation.
        */
       brw_fill_flag(bld, any ? 0 : 0xFFFFFFFF);
       bld.CMP(bld.null_reg_ud(), src, brw_imm_ud(0u), BRW_CONDITIONAL_NZ);
       bld.exec_all().MOV(retype(dst, BRW_TYPE_UD), brw_imm_ud(0));
    
       /* Before Xe2, we can use specialized predicates. */
       const enum brw_predicate pred = any ? BRW_PREDICATE_ALIGN1_ANY4H
                                           : BRW_PREDICATE_ALIGN1_ALL4H;
    
       fs_inst *mov = bld.MOV(retype(dst, BRW_TYPE_D), brw_imm_d(-1));
       set_predicate(pred, mov);
    }
    
    static void
    brw_lower_quad_vote_gfx20(const brw_builder &bld, enum opcode opcode, brw_reg dst, brw_reg src)
    {
       assert(opcode == SHADER_OPCODE_VOTE_ANY || opcode == SHADER_OPCODE_VOTE_ALL);
       const bool any = opcode == SHADER_OPCODE_VOTE_ANY;
    
       /* This code is going to manipulate the results of flag mask, so clear it to
        * avoid any residual value from disabled channels.
        */
       brw_reg flag = brw_fill_flag(bld, 0);
    
       /* Mask of invocations where condition is true, note that mask is
        * replicated to each invocation.
        */
       bld.CMP(bld.null_reg_ud(), src, brw_imm_ud(0u), BRW_CONDITIONAL_NZ);
       brw_reg cond_mask = bld.vgrf(BRW_TYPE_UD);
       bld.MOV(cond_mask, flag);
    
       /* Mask of invocations in the quad, each invocation will get
        * all the bits set for their quad, i.e. invocations 0-3 will have
        * 0b...1111, invocations 4-7 will have 0b...11110000 and so on.
        */
       brw_reg invoc_ud = bld.vgrf(BRW_TYPE_UD);
       bld.MOV(invoc_ud, bld.LOAD_SUBGROUP_INVOCATION());
       brw_reg quad_mask =
          bld.SHL(brw_imm_ud(0xF), bld.AND(invoc_ud, brw_imm_ud(0xFFFFFFFC)));
    
       /* An invocation will have bits set for each quad that passes the
        * condition.  This is uniform among each quad.
        */
       brw_reg tmp = bld.AND(cond_mask, quad_mask);
    
       if (any) {
          bld.CMP(retype(dst, BRW_TYPE_UD), tmp, brw_imm_ud(0), BRW_CONDITIONAL_NZ);
       } else {
          /* Filter out quad_mask to include only active channels. */
          brw_reg active = bld.vgrf(BRW_TYPE_UD);
          bld.exec_all().emit(SHADER_OPCODE_LOAD_LIVE_CHANNELS, active);
          bld.MOV(active, brw_reg(component(active, 0)));
          bld.AND(quad_mask, quad_mask, active);
    
          bld.CMP(retype(dst, BRW_TYPE_UD), tmp, quad_mask, BRW_CONDITIONAL_Z);
       }
    }
    
    static bool
    brw_lower_vote(fs_visitor &s, bblock_t *block, fs_inst *inst)
    {
       const brw_builder bld(&s, block, inst);
    
       brw_reg dst = inst->dst;
       brw_reg src = inst->src[0];
    
       unsigned cluster_size;
       if (inst->sources > 1) {
          assert(inst->src[1].file == IMM);
          cluster_size = inst->src[1].ud;
       } else {
          cluster_size = s.dispatch_width;
       }
    
       if (cluster_size == s.dispatch_width) {
          brw_lower_dispatch_width_vote(bld, inst->opcode, dst, src);
       } else {
          assert(cluster_size == 4);
          if (s.devinfo->ver < 20)
             brw_lower_quad_vote_gfx9(bld, inst->opcode, dst, src);
          else
             brw_lower_quad_vote_gfx20(bld, inst->opcode, dst, src);
       }
    
       inst->remove(block);
       return true;
    }
    
    static bool
    brw_lower_ballot(fs_visitor &s, bblock_t *block, fs_inst *inst)
    {
       const brw_builder bld(&s, block, inst);
    
       brw_reg value = retype(inst->src[0], BRW_TYPE_UD);
       brw_reg dst = inst->dst;
    
       const brw_builder xbld = dst.is_scalar ? bld.scalar_group() : bld;
    
       if (value.file == IMM) {
          /* Implement a fast-path for ballot(true). */
          if (!value.is_zero()) {
             brw_reg tmp = bld.vgrf(BRW_TYPE_UD);
             bld.exec_all().emit(SHADER_OPCODE_LOAD_LIVE_CHANNELS, tmp);
             xbld.MOV(dst, brw_reg(component(tmp, 0)));
          } else {
             brw_reg zero = retype(brw_imm_uq(0), dst.type);
             xbld.MOV(dst, zero);
          }
       } else {
          brw_reg flag = brw_fill_flag(bld, 0);
          bld.CMP(bld.null_reg_ud(), value, brw_imm_ud(0u), BRW_CONDITIONAL_NZ);
          xbld.MOV(dst, flag);
       }
    
       inst->remove(block);
       return true;
    }
    
    static bool
    brw_lower_quad_swap(fs_visitor &s, bblock_t *block, fs_inst *inst)
    {
       const brw_builder bld(&s, block, inst);
    
       assert(inst->dst.type == inst->src[0].type);
       brw_reg dst = inst->dst;
       brw_reg value = inst->src[0];
    
       assert(inst->src[1].file == IMM);
       enum brw_swap_direction dir = (enum brw_swap_direction)inst->src[1].ud;
    
       switch (dir) {
       case BRW_SWAP_HORIZONTAL: {
          const brw_reg tmp = bld.vgrf(value.type);
    
          const brw_builder ubld = bld.exec_all().group(s.dispatch_width / 2, 0);
    
          const brw_reg src_left = horiz_stride(value, 2);
          const brw_reg src_right = horiz_stride(horiz_offset(value, 1), 2);
          const brw_reg tmp_left = horiz_stride(tmp, 2);
          const brw_reg tmp_right = horiz_stride(horiz_offset(tmp, 1), 2);
    
          ubld.MOV(tmp_left, src_right);
          ubld.MOV(tmp_right, src_left);
    
          bld.MOV(retype(dst, value.type), tmp);
          break;
       }
       case BRW_SWAP_VERTICAL:
       case BRW_SWAP_DIAGONAL: {
          if (brw_type_size_bits(value.type) == 32) {
             /* For 32-bit, we can use a SIMD4x2 instruction to do this easily */
             const unsigned swizzle = dir == BRW_SWAP_VERTICAL ? BRW_SWIZZLE4(2,3,0,1)
                                                               : BRW_SWIZZLE4(3,2,1,0);
             const brw_reg tmp = bld.vgrf(value.type);
             const brw_builder ubld = bld.exec_all();
             ubld.emit(SHADER_OPCODE_QUAD_SWIZZLE, tmp, value, brw_imm_ud(swizzle));
             bld.MOV(dst, tmp);
          } else {
             /* For larger data types, we have to either emit dispatch_width many
              * MOVs or else fall back to doing indirects.
              */
             const unsigned xor_mask = dir == BRW_SWAP_VERTICAL ? 0x2 : 0x3;
             brw_reg idx = bld.vgrf(BRW_TYPE_W);
             bld.XOR(idx, bld.LOAD_SUBGROUP_INVOCATION(), brw_imm_w(xor_mask));
             bld.emit(SHADER_OPCODE_SHUFFLE, dst, value, idx);
          }
          break;
       }
       }
    
       inst->remove(block);
       return true;
    }
    
    static bool
    brw_lower_read_from_live_channel(fs_visitor &s, bblock_t *block, fs_inst *inst)
    {
       const brw_builder bld(&s, block, inst);
    
       assert(inst->sources == 1);
       assert(inst->dst.type == inst->src[0].type);
       brw_reg dst = inst->dst;
       brw_reg value = inst->src[0];
    
       bld.MOV(dst, bld.emit_uniformize(value));
    
       inst->remove(block);
       return true;
    }
    
    static bool
    brw_lower_read_from_channel(fs_visitor &s, bblock_t *block, fs_inst *inst)
    {
       const brw_builder bld(&s, block, inst);
    
       assert(inst->sources == 2);
       assert(inst->dst.type == inst->src[0].type);
    
       brw_reg dst = inst->dst;
       brw_reg value = inst->src[0];
       brw_reg index = retype(inst->src[1], BRW_TYPE_UD);
    
       /* When for some reason the subgroup_size picked by NIR is larger than
        * the dispatch size picked by the backend (this could happen in RT,
        * FS), bound the invocation to the dispatch size.
        */
       const unsigned dispatch_width_mask = s.dispatch_width - 1;
    
       if (index.file == IMM) {
          /* Always apply mask here since it is cheap. */
          bld.MOV(dst, component(value, index.ud & dispatch_width_mask));
       } else {
          if (s.api_subgroup_size == 0 || s.dispatch_width < s.api_subgroup_size)
             index = bld.AND(index, brw_imm_ud(dispatch_width_mask));
    
          brw_reg tmp = bld.BROADCAST(value, bld.emit_uniformize(index));
          bld.MOV(dst, tmp);
       }
    
       inst->remove(block);
       return true;
    }
    
    bool
    brw_lower_subgroup_ops(fs_visitor &s)
    {
       bool progress = false;
    
       foreach_block_and_inst_safe(block, fs_inst, inst, s.cfg) {
          switch (inst->opcode) {
          case SHADER_OPCODE_REDUCE:
             progress |= brw_lower_reduce(s, block, inst);
             break;
    
          case SHADER_OPCODE_INCLUSIVE_SCAN:
          case SHADER_OPCODE_EXCLUSIVE_SCAN:
             progress |= brw_lower_scan(s, block, inst);
             break;
    
          case SHADER_OPCODE_VOTE_ANY:
          case SHADER_OPCODE_VOTE_ALL:
          case SHADER_OPCODE_VOTE_EQUAL:
             progress |= brw_lower_vote(s, block, inst);
             break;
    
          case SHADER_OPCODE_BALLOT:
             progress |= brw_lower_ballot(s, block, inst);
             break;
    
          case SHADER_OPCODE_QUAD_SWAP:
             progress |= brw_lower_quad_swap(s, block, inst);
             break;
    
          case SHADER_OPCODE_READ_FROM_LIVE_CHANNEL:
             progress |= brw_lower_read_from_live_channel(s, block, inst);
             break;
    
          case SHADER_OPCODE_READ_FROM_CHANNEL:
             progress |= brw_lower_read_from_channel(s, block, inst);
             break;
    
          default:
             /* Nothing to do. */
             break;
          }
       }
    
       if (progress)
          s.invalidate_analysis(DEPENDENCY_INSTRUCTIONS | DEPENDENCY_VARIABLES);
    
       return progress;
    }