path: root/src/amd/compiler/aco_optimizer_postRA.cpp

/*
 * Copyright © 2021 Valve 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 "aco_builder.h"
#include "aco_ir.h"

#include <algorithm>
#include <array>
#include <bitset>
#include <vector>

namespace aco {
namespace {

constexpr const size_t max_reg_cnt = 512;
constexpr const size_t max_sgpr_cnt = 128;
constexpr const size_t min_vgpr = 256;
constexpr const size_t max_vgpr_cnt = 256;

struct Idx {
   bool operator==(const Idx& other) const { return block == other.block && instr == other.instr; }
   bool operator!=(const Idx& other) const { return !operator==(other); }

   bool found() const { return block != UINT32_MAX; }

   uint32_t block;
   uint32_t instr;
};

/** Indicates that a register was not yet written in the shader. */
Idx not_written_yet{UINT32_MAX, 0};

/** Indicates that an operand is constant or undefined, not written by any instruction. */
Idx const_or_undef{UINT32_MAX, 2};

/** Indicates that a register was overwritten by different instructions in previous blocks. */
Idx overwritten_untrackable{UINT32_MAX, 3};

/** Indicates that a register was written by subdword operations. */
Idx overwritten_subdword{UINT32_MAX, 4};

struct pr_opt_ctx {
   using Idx_array = std::array<Idx, max_reg_cnt>;

   Program* program;
   Block* current_block;
   uint32_t current_instr_idx;
   std::vector<uint16_t> uses;
   std::unique_ptr<Idx_array[]> instr_idx_by_regs;

   pr_opt_ctx(Program* p)
       : program(p), current_block(nullptr), current_instr_idx(0), uses(dead_code_analysis(p)),
         instr_idx_by_regs(std::unique_ptr<Idx_array[]>{new Idx_array[p->blocks.size()]})
   {}

   ALWAYS_INLINE void reset_block_regs(const std::vector<uint32_t>& preds,
                                       const unsigned block_index, const unsigned min_reg,
                                       const unsigned num_regs)
   {
      const unsigned num_preds = preds.size();
      const unsigned first_pred = preds[0];

      /* Copy information from the first predecessor. */
      memcpy(&instr_idx_by_regs[block_index][min_reg], &instr_idx_by_regs[first_pred][min_reg],
             num_regs * sizeof(Idx));

      /* Mark overwritten if it doesn't match with other predecessors. */
      const unsigned until_reg = min_reg + num_regs;
      for (unsigned i = 1; i < num_preds; ++i) {
         unsigned pred = preds[i];
         for (unsigned reg = min_reg; reg < until_reg; ++reg) {
            Idx& idx = instr_idx_by_regs[block_index][reg];
            if (idx == overwritten_untrackable)
               continue;

            if (idx != instr_idx_by_regs[pred][reg])
               idx = overwritten_untrackable;
         }
      }
   }

   void reset_block(Block* block)
   {
      current_block = block;
      current_instr_idx = 0;

      if (block->linear_preds.empty()) {
         std::fill(instr_idx_by_regs[block->index].begin(), instr_idx_by_regs[block->index].end(),
                   not_written_yet);
      } else if (block->kind & block_kind_loop_header) {
         /* Instructions inside the loop may overwrite registers of temporaries that are
          * not live inside the loop, but we can't detect that because we haven't processed
          * the blocks in the loop yet. As a workaround, mark all registers as untrackable.
          * TODO: Consider improving this in the future.
          */
         std::fill(instr_idx_by_regs[block->index].begin(), instr_idx_by_regs[block->index].end(),
                   overwritten_untrackable);
      } else {
         reset_block_regs(block->linear_preds, block->index, 0, max_sgpr_cnt);
         reset_block_regs(block->linear_preds, block->index, 251, 3);

         if (!block->logical_preds.empty()) {
            /* We assume that VGPRs are only read by blocks which have a logical predecessor,
             * ie. any block that reads any VGPR has at least 1 logical predecessor.
             */
            reset_block_regs(block->logical_preds, block->index, min_vgpr, max_vgpr_cnt);
         } else {
            /* If a block has no logical predecessors, it is not part of the
             * logical CFG and therefore it also won't have any logical successors.
             * Such a block does not write any VGPRs ever.
             */
            assert(block->logical_succs.empty());
         }
      }
   }

   Instruction* get(Idx idx) { return program->blocks[idx.block].instructions[idx.instr].get(); }
};

void
save_reg_writes(pr_opt_ctx& ctx, aco_ptr<Instruction>& instr)
{
   for (const Definition& def : instr->definitions) {
      assert(def.regClass().type() != RegType::sgpr || def.physReg().reg() <= 255);
      assert(def.regClass().type() != RegType::vgpr || def.physReg().reg() >= 256);

      unsigned dw_size = DIV_ROUND_UP(def.bytes(), 4u);
      unsigned r = def.physReg().reg();
      Idx idx{ctx.current_block->index, ctx.current_instr_idx};

      if (def.regClass().is_subdword())
         idx = overwritten_subdword;

      assert((r + dw_size) <= max_reg_cnt);
      assert(def.size() == dw_size || def.regClass().is_subdword());
      std::fill(ctx.instr_idx_by_regs[ctx.current_block->index].begin() + r,
                ctx.instr_idx_by_regs[ctx.current_block->index].begin() + r + dw_size, idx);
   }
}

Idx
last_writer_idx(pr_opt_ctx& ctx, PhysReg physReg, RegClass rc)
{
   /* Verify that all of the operand's registers are written by the same instruction. */
   assert(physReg.reg() < max_reg_cnt);
   Idx instr_idx = ctx.instr_idx_by_regs[ctx.current_block->index][physReg.reg()];
   unsigned dw_size = DIV_ROUND_UP(rc.bytes(), 4u);
   unsigned r = physReg.reg();
   bool all_same =
      std::all_of(ctx.instr_idx_by_regs[ctx.current_block->index].begin() + r,
                  ctx.instr_idx_by_regs[ctx.current_block->index].begin() + r + dw_size,
                  [instr_idx](Idx i) { return i == instr_idx; });

   return all_same ? instr_idx : overwritten_untrackable;
}

Idx
last_writer_idx(pr_opt_ctx& ctx, const Operand& op)
{
   if (op.isConstant() || op.isUndefined())
      return const_or_undef;

   return last_writer_idx(ctx, op.physReg(), op.regClass());
}

/**
 * Check whether a register has been overwritten since the given location.
 * This is an important part of checking whether certain optimizations are
 * valid.
 * Note that the decision is made based on registers and not on SSA IDs.
 */
bool
is_overwritten_since(pr_opt_ctx& ctx, PhysReg reg, RegClass rc, const Idx& since_idx)
{
   /* If we didn't find an instruction, assume that the register is overwritten. */
   if (!since_idx.found())
      return true;

   /* TODO: We currently can't keep track of subdword registers. */
   if (rc.is_subdword())
      return true;

   unsigned begin_reg = reg.reg();
   unsigned end_reg = begin_reg + rc.size();
   unsigned current_block_idx = ctx.current_block->index;

   for (unsigned r = begin_reg; r < end_reg; ++r) {
      Idx& i = ctx.instr_idx_by_regs[current_block_idx][r];
      if (i == overwritten_untrackable && current_block_idx > since_idx.block)
         return true;
      else if (i == overwritten_untrackable || i == not_written_yet)
         continue;

      assert(i.found());

      if (i.block > since_idx.block || (i.block == since_idx.block && i.instr > since_idx.instr))
         return true;
   }

   return false;
}

template <typename T>
bool
is_overwritten_since(pr_opt_ctx& ctx, const T& t, const Idx& idx)
{
   return is_overwritten_since(ctx, t.physReg(), t.regClass(), idx);
}

void
try_apply_branch_vcc(pr_opt_ctx& ctx, aco_ptr<Instruction>& instr)
{
   /* We are looking for the following pattern:
    *
    * vcc = ...                      ; last_vcc_wr
    * sX, scc = s_and_bXX vcc, exec  ; op0_instr
    * (...vcc and exec must not be overwritten inbetween...)
    * s_cbranch_XX scc               ; instr
    *
    * If possible, the above is optimized into:
    *
    * vcc = ...                      ; last_vcc_wr
    * s_cbranch_XX vcc               ; instr modified to use vcc
    */

   /* Don't try to optimize this on GFX6-7 because SMEM may corrupt the vccz bit. */
   if (ctx.program->gfx_level < GFX8)
      return;

   if (instr->format != Format::PSEUDO_BRANCH || instr->operands.size() == 0 ||
       instr->operands[0].physReg() != scc)
      return;

   Idx op0_instr_idx = last_writer_idx(ctx, instr->operands[0]);
   Idx last_vcc_wr_idx = last_writer_idx(ctx, vcc, ctx.program->lane_mask);

   /* We need to make sure:
    * - the instructions that wrote the operand register and VCC are both found
    * - the operand register used by the branch, and VCC were both written in the current block
    * - EXEC hasn't been overwritten since the last VCC write
    * - VCC hasn't been overwritten since the operand register was written
    *   (ie. the last VCC writer precedes the op0 writer)
    */
   if (!op0_instr_idx.found() || !last_vcc_wr_idx.found() ||
       op0_instr_idx.block != ctx.current_block->index ||
       last_vcc_wr_idx.block != ctx.current_block->index ||
       is_overwritten_since(ctx, exec, ctx.program->lane_mask, last_vcc_wr_idx) ||
       is_overwritten_since(ctx, vcc, ctx.program->lane_mask, op0_instr_idx))
      return;

   Instruction* op0_instr = ctx.get(op0_instr_idx);
   Instruction* last_vcc_wr = ctx.get(last_vcc_wr_idx);

   if ((op0_instr->opcode != aco_opcode::s_and_b64 /* wave64 */ &&
        op0_instr->opcode != aco_opcode::s_and_b32 /* wave32 */) ||
       op0_instr->operands[0].physReg() != vcc || op0_instr->operands[1].physReg() != exec ||
       !last_vcc_wr->isVOPC())
      return;

   assert(last_vcc_wr->definitions[0].tempId() == op0_instr->operands[0].tempId());

   /* Reduce the uses of the SCC def */
   ctx.uses[instr->operands[0].tempId()]--;
   /* Use VCC instead of SCC in the branch */
   instr->operands[0] = op0_instr->operands[0];
}

void
try_optimize_scc_nocompare(pr_opt_ctx& ctx, aco_ptr<Instruction>& instr)
{
   /* We are looking for the following pattern:
    *
    * s_bfe_u32 s0, s3, 0x40018  ; outputs SGPR and SCC if the SGPR != 0
    * s_cmp_eq_i32 s0, 0         ; comparison between the SGPR and 0
    * s_cbranch_scc0 BB3         ; use the result of the comparison, eg. branch or cselect
    *
    * If possible, the above is optimized into:
    *
    * s_bfe_u32 s0, s3, 0x40018  ; original instruction
    * s_cbranch_scc1 BB3         ; modified to use SCC directly rather than the SGPR with comparison
    *
    */

   if (!instr->isSALU() && !instr->isBranch())
      return;

   if (instr->isSOPC() &&
       (instr->opcode == aco_opcode::s_cmp_eq_u32 || instr->opcode == aco_opcode::s_cmp_eq_i32 ||
        instr->opcode == aco_opcode::s_cmp_lg_u32 || instr->opcode == aco_opcode::s_cmp_lg_i32 ||
        instr->opcode == aco_opcode::s_cmp_eq_u64 || instr->opcode == aco_opcode::s_cmp_lg_u64) &&
       (instr->operands[0].constantEquals(0) || instr->operands[1].constantEquals(0)) &&
       (instr->operands[0].isTemp() || instr->operands[1].isTemp())) {
      /* Make sure the constant is always in operand 1 */
      if (instr->operands[0].isConstant())
         std::swap(instr->operands[0], instr->operands[1]);

      if (ctx.uses[instr->operands[0].tempId()] > 1)
         return;

      /* Find the writer instruction of Operand 0. */
      Idx wr_idx = last_writer_idx(ctx, instr->operands[0]);
      if (!wr_idx.found())
         return;

      Instruction* wr_instr = ctx.get(wr_idx);
      if (!wr_instr->isSALU() || wr_instr->definitions.size() < 2 ||
          wr_instr->definitions[1].physReg() != scc)
         return;

      /* Look for instructions which set SCC := (D != 0) */
      switch (wr_instr->opcode) {
      case aco_opcode::s_bfe_i32:
      case aco_opcode::s_bfe_i64:
      case aco_opcode::s_bfe_u32:
      case aco_opcode::s_bfe_u64:
      case aco_opcode::s_and_b32:
      case aco_opcode::s_and_b64:
      case aco_opcode::s_andn2_b32:
      case aco_opcode::s_andn2_b64:
      case aco_opcode::s_or_b32:
      case aco_opcode::s_or_b64:
      case aco_opcode::s_orn2_b32:
      case aco_opcode::s_orn2_b64:
      case aco_opcode::s_xor_b32:
      case aco_opcode::s_xor_b64:
      case aco_opcode::s_not_b32:
      case aco_opcode::s_not_b64:
      case aco_opcode::s_nor_b32:
      case aco_opcode::s_nor_b64:
      case aco_opcode::s_xnor_b32:
      case aco_opcode::s_xnor_b64:
      case aco_opcode::s_nand_b32:
      case aco_opcode::s_nand_b64:
      case aco_opcode::s_lshl_b32:
      case aco_opcode::s_lshl_b64:
      case aco_opcode::s_lshr_b32:
      case aco_opcode::s_lshr_b64:
      case aco_opcode::s_ashr_i32:
      case aco_opcode::s_ashr_i64:
      case aco_opcode::s_abs_i32:
      case aco_opcode::s_absdiff_i32: break;
      default: return;
      }

      /* Check whether both SCC and Operand 0 are written by the same instruction. */
      Idx sccwr_idx = last_writer_idx(ctx, scc, s1);
      if (wr_idx != sccwr_idx) {
         /* Check whether the current instruction is the only user of its first operand. */
         if (ctx.uses[wr_instr->definitions[1].tempId()] ||
             ctx.uses[wr_instr->definitions[0].tempId()] > 1)
            return;

         /* Check whether the operands of the writer are overwritten. */
         for (const Operand& op : wr_instr->operands) {
            if (!op.isConstant() && is_overwritten_since(ctx, op, wr_idx))
               return;
         }

         aco_opcode pulled_opcode = wr_instr->opcode;
         if (instr->opcode == aco_opcode::s_cmp_eq_u32 ||
             instr->opcode == aco_opcode::s_cmp_eq_i32 ||
             instr->opcode == aco_opcode::s_cmp_eq_u64) {
            /* When s_cmp_eq is used, it effectively inverts the SCC def.
             * However, we can't simply invert the opcodes here because that
             * would change the meaning of the program.
             */
            return;
         }

         Definition scc_def = instr->definitions[0];
         ctx.uses[wr_instr->definitions[0].tempId()]--;

         /* Copy the writer instruction, but use SCC from the current instr.
          * This means that the original instruction will be eliminated.
          */
         if (wr_instr->format == Format::SOP2) {
            instr.reset(create_instruction<SOP2_instruction>(pulled_opcode, Format::SOP2, 2, 2));
            instr->operands[1] = wr_instr->operands[1];
         } else if (wr_instr->format == Format::SOP1) {
            instr.reset(create_instruction<SOP1_instruction>(pulled_opcode, Format::SOP1, 1, 2));
         }
         instr->definitions[0] = wr_instr->definitions[0];
         instr->definitions[1] = scc_def;
         instr->operands[0] = wr_instr->operands[0];
         return;
      }

      /* Use the SCC def from wr_instr */
      ctx.uses[instr->operands[0].tempId()]--;
      instr->operands[0] = Operand(wr_instr->definitions[1].getTemp(), scc);
      ctx.uses[instr->operands[0].tempId()]++;

      /* Set the opcode and operand to 32-bit */
      instr->operands[1] = Operand::zero();
      instr->opcode =
         (instr->opcode == aco_opcode::s_cmp_eq_u32 || instr->opcode == aco_opcode::s_cmp_eq_i32 ||
          instr->opcode == aco_opcode::s_cmp_eq_u64)
            ? aco_opcode::s_cmp_eq_u32
            : aco_opcode::s_cmp_lg_u32;
   } else if ((instr->format == Format::PSEUDO_BRANCH && instr->operands.size() == 1 &&
               instr->operands[0].physReg() == scc) ||
              instr->opcode == aco_opcode::s_cselect_b32 ||
              instr->opcode == aco_opcode::s_cselect_b64) {

      /* For cselect, operand 2 is the SCC condition */
      unsigned scc_op_idx = 0;
      if (instr->opcode == aco_opcode::s_cselect_b32 ||
          instr->opcode == aco_opcode::s_cselect_b64) {
         scc_op_idx = 2;
      }

      Idx wr_idx = last_writer_idx(ctx, instr->operands[scc_op_idx]);
      if (!wr_idx.found())
         return;

      Instruction* wr_instr = ctx.get(wr_idx);

      /* Check if we found the pattern above. */
      if (wr_instr->opcode != aco_opcode::s_cmp_eq_u32 &&
          wr_instr->opcode != aco_opcode::s_cmp_lg_u32)
         return;
      if (wr_instr->operands[0].physReg() != scc)
         return;
      if (!wr_instr->operands[1].constantEquals(0))
         return;

      /* The optimization can be unsafe when there are other users. */
      if (ctx.uses[instr->operands[scc_op_idx].tempId()] > 1)
         return;

      if (wr_instr->opcode == aco_opcode::s_cmp_eq_u32) {
         /* Flip the meaning of the instruction to correctly use the SCC. */
         if (instr->format == Format::PSEUDO_BRANCH)
            instr->opcode = instr->opcode == aco_opcode::p_cbranch_z ? aco_opcode::p_cbranch_nz
                                                                     : aco_opcode::p_cbranch_z;
         else if (instr->opcode == aco_opcode::s_cselect_b32 ||
                  instr->opcode == aco_opcode::s_cselect_b64)
            std::swap(instr->operands[0], instr->operands[1]);
         else
            unreachable(
               "scc_nocompare optimization is only implemented for p_cbranch and s_cselect");
      }

      /* Use the SCC def from the original instruction, not the comparison */
      ctx.uses[instr->operands[scc_op_idx].tempId()]--;
      instr->operands[scc_op_idx] = wr_instr->operands[0];
   }
}

void
try_combine_dpp(pr_opt_ctx& ctx, aco_ptr<Instruction>& instr)
{
   /* We are looking for the following pattern:
    *
    * v_mov_dpp vA, vB, ...      ; move instruction with DPP
    * v_xxx vC, vA, ...          ; current instr that uses the result from the move
    *
    * If possible, the above is optimized into:
    *
    * v_xxx_dpp vC, vB, ...      ; current instr modified to use DPP directly
    *
    */

   if (!instr->isVALU() || instr->isDPP())
      return;

   for (unsigned i = 0; i < instr->operands.size(); i++) {
      Idx op_instr_idx = last_writer_idx(ctx, instr->operands[i]);
      if (!op_instr_idx.found())
         continue;

      const Instruction* mov = ctx.get(op_instr_idx);
      if (mov->opcode != aco_opcode::v_mov_b32 || !mov->isDPP())
         continue;

      /* If we aren't going to remove the v_mov_b32, we have to ensure that it doesn't overwrite
       * it's own operand before we use it.
       */
      if (mov->definitions[0].physReg() == mov->operands[0].physReg() &&
          (!mov->definitions[0].tempId() || ctx.uses[mov->definitions[0].tempId()] > 1))
         continue;

      /* Don't propagate DPP if the source register is overwritten since the move. */
      if (is_overwritten_since(ctx, mov->operands[0], op_instr_idx))
         continue;

      /* We won't eliminate the DPP mov if the operand is used twice */
      bool op_used_twice = false;
      for (unsigned j = 0; j < instr->operands.size(); j++)
         op_used_twice |= i != j && instr->operands[i] == instr->operands[j];
      if (op_used_twice)
         continue;

      bool dpp8 = mov->isDPP8();
      bool input_mods = instr_info.can_use_input_modifiers[(int)instr->opcode] &&
                        instr_info.operand_size[(int)instr->opcode] == 32;
      bool mov_uses_mods = mov->valu().neg[0] || mov->valu().abs[0];
      if (((dpp8 && ctx.program->gfx_level < GFX11) || !input_mods) && mov_uses_mods)
         continue;

      if (i != 0) {
         if (!can_swap_operands(instr, &instr->opcode, 0, i))
            continue;
         std::swap(instr->operands[0], instr->operands[i]);
         instr->valu().neg[0].swap(instr->valu().neg[i]);
         instr->valu().abs[0].swap(instr->valu().abs[i]);
         instr->valu().opsel[0].swap(instr->valu().opsel[i]);
         instr->valu().opsel_lo[0].swap(instr->valu().opsel_lo[i]);
         instr->valu().opsel_hi[0].swap(instr->valu().opsel_hi[i]);
      }

      if (!can_use_DPP(ctx.program->gfx_level, instr, dpp8))
         continue;

      if (!dpp8) /* anything else doesn't make sense in SSA */
         assert(mov->dpp16().row_mask == 0xf && mov->dpp16().bank_mask == 0xf);

      if (--ctx.uses[mov->definitions[0].tempId()])
         ctx.uses[mov->operands[0].tempId()]++;

      convert_to_DPP(ctx.program->gfx_level, instr, dpp8);

      instr->operands[0] = mov->operands[0];

      if (dpp8) {
         DPP8_instruction* dpp = &instr->dpp8();
         memcpy(dpp->lane_sel, mov->dpp8().lane_sel, sizeof(dpp->lane_sel));
         if (mov_uses_mods)
            instr->format = asVOP3(instr->format);
      } else {
         DPP16_instruction* dpp = &instr->dpp16();
         dpp->dpp_ctrl = mov->dpp16().dpp_ctrl;
         dpp->bound_ctrl = true;
      }
      instr->valu().neg[0] ^= mov->valu().neg[0] && !instr->valu().abs[0];
      instr->valu().abs[0] |= mov->valu().abs[0];
      return;
   }
}

unsigned
num_encoded_alu_operands(const aco_ptr<Instruction>& instr)
{
   if (instr->isSALU()) {
      if (instr->isSOP2())
         return 2;
      else if (instr->isSOP1())
         return 1;

      return 0;
   }

   if (instr->isVALU()) {
      if (instr->isVOP1())
         return 1;
      else if (instr->isVOPC() || instr->isVOP2())
         return 2;
      else if (instr->opcode == aco_opcode::v_writelane_b32_e64 ||
               instr->opcode == aco_opcode::v_writelane_b32)
         return 2; /* potentially VOP3, but reads VDST as SRC2 */
      else if (instr->isVOP3() || instr->isVOP3P() || instr->isVINTERP_INREG())
         return instr->operands.size();
   }

   return 0;
}

void
try_reassign_split_vector(pr_opt_ctx& ctx, aco_ptr<Instruction>& instr)
{
   /* Any unused split_vector definition can always use the same register
    * as the operand. This avoids creating unnecessary copies.
    */
   if (instr->opcode == aco_opcode::p_split_vector) {
      Operand& op = instr->operands[0];
      if (!op.isTemp() || op.isKill())
         return;

      PhysReg reg = op.physReg();
      for (Definition& def : instr->definitions) {
         if (def.getTemp().type() == op.getTemp().type() && def.isKill())
            def.setFixed(reg);

         reg = reg.advance(def.bytes());
      }

      return;
   }

   /* We are looking for the following pattern:
    *
    * sA, sB = p_split_vector s[X:Y]
    * ... X and Y not overwritten here ...
    * use sA or sB <--- current instruction
    *
    * If possible, we propagate the registers from the p_split_vector
    * operand into the current instruction and the above is optimized into:
    *
    * use sX or sY
    *
    * Thereby, we might violate register assignment rules.
    * This optimization exists because it's too difficult to solve it
    * in RA, and should be removed after we solved this in RA.
    */

   if (!instr->isVALU() && !instr->isSALU())
      return;

   for (unsigned i = 0; i < num_encoded_alu_operands(instr); i++) {
      /* Find the instruction that writes the current operand. */
      const Operand& op = instr->operands[i];
      Idx op_instr_idx = last_writer_idx(ctx, op);
      if (!op_instr_idx.found())
         continue;

      /* Check if the operand is written by p_split_vector. */
      Instruction* split_vec = ctx.get(op_instr_idx);
      if (split_vec->opcode != aco_opcode::p_split_vector &&
          split_vec->opcode != aco_opcode::p_extract_vector)
         continue;

      Operand& split_op = split_vec->operands[0];

      /* Don't do anything if the p_split_vector operand is not a temporary
       * or is killed by the p_split_vector.
       * In this case the definitions likely already reuse the same registers as the operand.
       */
      if (!split_op.isTemp() || split_op.isKill())
         continue;

      /* Only propagate operands of the same type */
      if (split_op.getTemp().type() != op.getTemp().type())
         continue;

      /* Check if the p_split_vector operand's registers are overwritten. */
      if (is_overwritten_since(ctx, split_op, op_instr_idx))
         continue;

      PhysReg reg = split_op.physReg();
      if (split_vec->opcode == aco_opcode::p_extract_vector) {
         reg =
            reg.advance(split_vec->definitions[0].bytes() * split_vec->operands[1].constantValue());
      }
      for (Definition& def : split_vec->definitions) {
         if (def.getTemp() != op.getTemp()) {
            reg = reg.advance(def.bytes());
            continue;
         }

         /* Don't propagate misaligned SGPRs.
          * Note: No ALU instruction can take a variable larger than 64bit.
          */
         if (op.regClass() == s2 && reg.reg() % 2 != 0)
            break;

         /* Sub dword operands might need updates to SDWA/opsel,
          * but we only track full register writes at the moment.
          */
         assert(op.physReg().byte() == reg.byte());

         /* If there is only one use (left), recolor the split_vector definition */
         if (ctx.uses[op.tempId()] == 1)
            def.setFixed(reg);
         else
            ctx.uses[op.tempId()]--;

         /* Use the p_split_vector operand register directly.
          *
          * Note: this might violate register assignment rules to some extend
          *       in case the definition does not get recolored, eventually.
          */
         instr->operands[i].setFixed(reg);
         break;
      }
   }
}

void
process_instruction(pr_opt_ctx& ctx, aco_ptr<Instruction>& instr)
{
   /* Don't try to optimize instructions which are already dead. */
   if (!instr || is_dead(ctx.uses, instr.get())) {
      instr.reset();
      ctx.current_instr_idx++;
      return;
   }

   try_apply_branch_vcc(ctx, instr);

   try_optimize_scc_nocompare(ctx, instr);

   try_combine_dpp(ctx, instr);

   try_reassign_split_vector(ctx, instr);

   if (instr)
      save_reg_writes(ctx, instr);

   ctx.current_instr_idx++;
}

} // namespace

void
optimize_postRA(Program* program)
{
   pr_opt_ctx ctx(program);

   /* Forward pass
    * Goes through each instruction exactly once, and can transform
    * instructions or adjust the use counts of temps.
    */
   for (auto& block : program->blocks) {
      ctx.reset_block(&block);

      for (aco_ptr<Instruction>& instr : block.instructions)
         process_instruction(ctx, instr);
   }

   /* Cleanup pass
    * Gets rid of instructions which are manually deleted or
    * no longer have any uses.
    */
   for (auto& block : program->blocks) {
      std::vector<aco_ptr<Instruction>> instructions;
      instructions.reserve(block.instructions.size());

      for (aco_ptr<Instruction>& instr : block.instructions) {
         if (!instr || is_dead(ctx.uses, instr.get()))
            continue;

         instructions.emplace_back(std::move(instr));
      }

      block.instructions = std::move(instructions);
   }
}

} // namespace aco