mirror of
https://github.com/vtil-project/VTIL-Core
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126 lines
No EOL
3.8 KiB
C++
126 lines
No EOL
3.8 KiB
C++
// Copyright (c) 2020 Can Boluk and contributors of the VTIL Project
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// All rights reserved.
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//
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// Redistribution and use in source and binary forms, with or without
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// modification, are permitted provided that the following conditions are met:
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//
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// 1. Redistributions of source code must retain the above copyright notice,
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// this list of conditions and the following disclaimer.
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// 2. Redistributions in binary form must reproduce the above copyright
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// notice, this list of conditions and the following disclaimer in the
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// documentation and/or other materials provided with the distribution.
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// 3. Neither the name of VTIL Project nor the names of its contributors
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// may be used to endorse or promote products derived from this software
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// without specific prior written permission.
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//
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// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
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// AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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// ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
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// LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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// CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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// SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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// CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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// ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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// POSSIBILITY OF SUCH DAMAGE.
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//
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#include "dead_code_elimination_pass.hpp"
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#include <vtil/utility>
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#include "../common/auxiliaries.hpp"
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namespace vtil::optimizer
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{
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// Returns whether the instruction is a semantic equivalent of NOP or not.
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//
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static bool is_semantic_nop( const instruction& ins )
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{
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if ( ins.base == &ins::mov ||
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ins.base == &ins::movsx )
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{
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if ( ins.operands[ 0 ] == ins.operands[ 1 ] )
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return true;
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}
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return false;
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}
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// Implement the pass.
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//
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size_t dead_code_elimination_pass::pass( basic_block* blk, bool xblock )
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{
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size_t counter = 0;
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if ( blk->empty() )
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return 0;
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auto [rbegin, rend] = reverse_iterators( *blk );
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for ( auto it = rbegin; it != rend; ++it )
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{
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// Skip if volatile or branching.
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//
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if ( it->base->is_branching() || it->is_volatile() )
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continue;
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// Check if results are used if not semantically nop.
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//
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bool used = false;
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if ( !is_semantic_nop( *it ) )
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{
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// Check register results:
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//
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for ( auto [op, type] : it->enum_operands() )
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{
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// Skip if not written to.
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//
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if ( type < operand_type::write )
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continue;
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// Create symbolic variable.
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//
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symbolic::variable var = { it, op.reg() };
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if ( used = aux::is_used( var, xblock, &ctrace ) )
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break;
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}
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// Check memory results:
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//
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if ( !used && it->base->writes_memory() )
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{
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auto [base, offset] = it->memory_location();
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symbolic::pointer ptr = { ctrace.trace_p( { it, base } ) + offset };
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if ( !( ptr.flags & register_stack_pointer ) )
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used = true;
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else
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used = aux::is_used( { it, { ptr, it->access_size() } }, xblock, &ctrace );
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}
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}
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// If result is not used, nop it.
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//
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if ( !used )
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{
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( +it )->base = &ins::nop;
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( +it )->operands = {};
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counter++;
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}
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}
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// Purge simplifier cache since block iterators are invalided thus cache may fail.
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//
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ctrace.flush( blk );
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if ( counter != 0 )
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symbolic::purge_simplifier_state();
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// Remove all nops.
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//
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for ( auto it = blk->begin(); !it.is_end(); )
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{
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if ( !it->is_volatile() && it->base == &ins::nop )
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it = blk->erase( it );
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else
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it++;
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}
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return counter;
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}
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}; |