223 lines
7.8 KiB
C++
223 lines
7.8 KiB
C++
// Copyright (c) 2017 The Khronos Group Inc.
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// Copyright (c) 2017 Valve Corporation
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// Copyright (c) 2017 LunarG Inc.
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// Copyright (c) 2019 Google LLC
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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#include "block_merge_util.h"
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namespace spvtools {
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namespace opt {
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namespace blockmergeutil {
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namespace {
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// Returns true if |block| contains a merge instruction.
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bool IsHeader(BasicBlock* block) { return block->GetMergeInst() != nullptr; }
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// Returns true if |id| contains a merge instruction.
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bool IsHeader(IRContext* context, uint32_t id) {
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return IsHeader(
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context->get_instr_block(context->get_def_use_mgr()->GetDef(id)));
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}
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// Returns true if |id| is the merge target of a merge instruction.
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bool IsMerge(IRContext* context, uint32_t id) {
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return !context->get_def_use_mgr()->WhileEachUse(
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id, [](Instruction* user, uint32_t index) {
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spv::Op op = user->opcode();
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if ((op == spv::Op::OpLoopMerge || op == spv::Op::OpSelectionMerge) &&
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index == 0u) {
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return false;
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}
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return true;
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});
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}
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// Returns true if |block| is the merge target of a merge instruction.
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bool IsMerge(IRContext* context, BasicBlock* block) {
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return IsMerge(context, block->id());
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}
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// Returns true if |id| is the continue target of a merge instruction.
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bool IsContinue(IRContext* context, uint32_t id) {
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return !context->get_def_use_mgr()->WhileEachUse(
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id, [](Instruction* user, uint32_t index) {
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spv::Op op = user->opcode();
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if (op == spv::Op::OpLoopMerge && index == 1u) {
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return false;
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}
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return true;
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});
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}
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// Removes any OpPhi instructions in |block|, which should have exactly one
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// predecessor, replacing uses of OpPhi ids with the ids associated with the
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// predecessor.
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void EliminateOpPhiInstructions(IRContext* context, BasicBlock* block) {
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block->ForEachPhiInst([context](Instruction* phi) {
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assert(2 == phi->NumInOperands() &&
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"A block can only have one predecessor for block merging to make "
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"sense.");
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context->ReplaceAllUsesWith(phi->result_id(),
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phi->GetSingleWordInOperand(0));
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context->KillInst(phi);
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});
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}
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} // Anonymous namespace
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bool CanMergeWithSuccessor(IRContext* context, BasicBlock* block) {
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// Find block with single successor which has no other predecessors.
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auto ii = block->end();
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--ii;
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Instruction* br = &*ii;
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if (br->opcode() != spv::Op::OpBranch) {
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return false;
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}
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const uint32_t lab_id = br->GetSingleWordInOperand(0);
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if (context->cfg()->preds(lab_id).size() != 1) {
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return false;
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}
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bool pred_is_merge = IsMerge(context, block);
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bool succ_is_merge = IsMerge(context, lab_id);
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if (pred_is_merge && succ_is_merge) {
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// Cannot merge two merges together.
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return false;
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}
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if (pred_is_merge && IsContinue(context, lab_id)) {
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// Cannot merge a continue target with a merge block.
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return false;
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}
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Instruction* merge_inst = block->GetMergeInst();
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const bool pred_is_header = IsHeader(block);
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if (pred_is_header && lab_id != merge_inst->GetSingleWordInOperand(0u)) {
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bool succ_is_header = IsHeader(context, lab_id);
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if (pred_is_header && succ_is_header) {
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// Cannot merge two headers together when the successor is not the merge
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// block of the predecessor.
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return false;
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}
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// If this is a header block and the successor is not its merge, we must
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// be careful about which blocks we are willing to merge together.
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// OpLoopMerge must be followed by a conditional or unconditional branch.
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// The merge must be a loop merge because a selection merge cannot be
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// followed by an unconditional branch.
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BasicBlock* succ_block = context->get_instr_block(lab_id);
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spv::Op succ_term_op = succ_block->terminator()->opcode();
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assert(merge_inst->opcode() == spv::Op::OpLoopMerge);
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if (succ_term_op != spv::Op::OpBranch &&
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succ_term_op != spv::Op::OpBranchConditional) {
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return false;
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}
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}
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if (succ_is_merge || IsContinue(context, lab_id)) {
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auto* struct_cfg = context->GetStructuredCFGAnalysis();
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auto switch_block_id = struct_cfg->ContainingSwitch(block->id());
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if (switch_block_id) {
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auto switch_merge_id = struct_cfg->SwitchMergeBlock(switch_block_id);
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const auto* switch_inst =
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&*block->GetParent()->FindBlock(switch_block_id)->tail();
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for (uint32_t i = 1; i < switch_inst->NumInOperands(); i += 2) {
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auto target_id = switch_inst->GetSingleWordInOperand(i);
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if (target_id == block->id() && target_id != switch_merge_id) {
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// Case constructs must be structurally dominated by the OpSwitch.
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// Since the successor is the merge/continue for another construct,
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// merging the blocks would break that requirement.
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return false;
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}
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}
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}
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}
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return true;
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}
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void MergeWithSuccessor(IRContext* context, Function* func,
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Function::iterator bi) {
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assert(CanMergeWithSuccessor(context, &*bi) &&
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"Precondition failure for MergeWithSuccessor: it must be legal to "
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"merge the block and its successor.");
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auto ii = bi->end();
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--ii;
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Instruction* br = &*ii;
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const uint32_t lab_id = br->GetSingleWordInOperand(0);
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Instruction* merge_inst = bi->GetMergeInst();
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bool pred_is_header = IsHeader(&*bi);
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// Merge blocks.
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context->KillInst(br);
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auto sbi = bi;
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for (; sbi != func->end(); ++sbi)
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if (sbi->id() == lab_id) break;
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// If bi is sbi's only predecessor, it dominates sbi and thus
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// sbi must follow bi in func's ordering.
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assert(sbi != func->end());
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if (sbi->tail()->opcode() == spv::Op::OpSwitch &&
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sbi->MergeBlockIdIfAny() != 0) {
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context->InvalidateAnalyses(IRContext::Analysis::kAnalysisStructuredCFG);
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}
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// Update the inst-to-block mapping for the instructions in sbi.
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for (auto& inst : *sbi) {
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context->set_instr_block(&inst, &*bi);
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}
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EliminateOpPhiInstructions(context, &*sbi);
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// Now actually move the instructions.
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bi->AddInstructions(&*sbi);
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if (merge_inst) {
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if (pred_is_header && lab_id == merge_inst->GetSingleWordInOperand(0u)) {
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// Merging the header and merge blocks, so remove the structured control
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// flow declaration.
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context->KillInst(merge_inst);
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} else {
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// Move OpLine/OpNoLine information to merge_inst. This solves
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// the validation error that OpLine is placed between OpLoopMerge
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// and OpBranchConditional.
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auto terminator = bi->terminator();
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auto& vec = terminator->dbg_line_insts();
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if (vec.size() > 0) {
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merge_inst->ClearDbgLineInsts();
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auto& new_vec = merge_inst->dbg_line_insts();
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new_vec.insert(new_vec.end(), vec.begin(), vec.end());
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terminator->ClearDbgLineInsts();
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for (auto& l_inst : new_vec)
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context->get_def_use_mgr()->AnalyzeInstDefUse(&l_inst);
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}
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// Clear debug scope of terminator to avoid DebugScope
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// emitted between terminator and merge.
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terminator->SetDebugScope(DebugScope(kNoDebugScope, kNoInlinedAt));
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// Move the merge instruction to just before the terminator.
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merge_inst->InsertBefore(terminator);
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}
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}
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context->ReplaceAllUsesWith(lab_id, bi->id());
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context->KillInst(sbi->GetLabelInst());
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(void)sbi.Erase();
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}
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} // namespace blockmergeutil
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} // namespace opt
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} // namespace spvtools
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