LLVMAliasAnalyzer.cc

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/*
    Copyright (c) 2002-2020 Tampere University.
 
    This file is part of TTA-Based Codesign Environment (TCE).
 
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/**
 * @file LLVMAliasAnalyzer.cc
 *
 * Implementation of LLVMAliasAnalyzer class.
 * 
 * This class uses LLVM AliasAnalysis and MachineInstruction references
 * in ProgramOperation to query for alises.
 *
 * @author Vladimír Guzma 2011 (vladimir.guzma-no.spam-tut.fi)
 * @note rating: red
 */
 
#include "CompilerWarnings.hh"
IGNORE_COMPILER_WARNING("-Wunused-parameter")
 
#include "LLVMAliasAnalyzer.hh"
 
#include "CompilerWarnings.hh"
IGNORE_COMPILER_WARNING("-Wunused-parameter")
IGNORE_COMPILER_WARNING("-Wcomment")
 
#include <llvm/CodeGen/MachineInstr.h>
#include "tce_config.h"
#include <llvm/IR/Value.h>
#include <llvm/CodeGen/MachineMemOperand.h>
 
#include <llvm/Analysis/AliasAnalysis.h>
 
 
#include "MoveNode.hh"
#include "Move.hh"
#include "DataDependenceGraph.hh"
#include "Terminal.hh"
 
POP_COMPILER_DIAGS
 
using namespace TTAProgram;
using namespace TTAMachine;
 
#define MayAlias llvm::AliasResult::Kind::MayAlias
#define PartialAlias llvm::AliasResult::Kind::PartialAlias
#define MustAlias llvm::AliasResult::Kind::MustAlias
#define NoAlias llvm::AliasResult::Kind::NoAlias
 
LLVMAliasAnalyzer::LLVMAliasAnalyzer(){
    AA_ = NULL;
}
 
bool 
LLVMAliasAnalyzer::isAddressTraceable(
    DataDependenceGraph& /*ddg*/, 
    const ProgramOperation& po) {
    // If the ProgramOperation has access to it's originating LLVM MachineInstr
    // and MachineInstr have some memory operands we can try tracing memory
    // accessed. 
    const llvm::MachineInstr* instr = po.machineInstr();    
    if (instr && !instr->memoperands_empty()) {
        return true;
    } else {
        return false;
    }
}
 
/**
 * Given two program operation, aswer question if memory accesed by those
 * operations aliases.
 *
 * If both POs access same memory returns true, if is sure the memory
 * is not same, returns false. Returns unknown in case memory accesses
 * may alias, or if there is partial alias.
 */
MemoryAliasAnalyzer::AliasingResult
LLVMAliasAnalyzer::analyze(
    DataDependenceGraph& ddg, 
    const ProgramOperation& pop1, 
    const ProgramOperation& pop2,
    MoveNodeUse::BBRelation bbInfo) {
 
    if (bbInfo) {
        return ALIAS_UNKNOWN;
    }
 
    if (!isAddressTraceable(ddg, pop1) || 
        !isAddressTraceable(ddg, pop2) ||
        AA_ == NULL) {
        return ALIAS_UNKNOWN;
    }
 
    const llvm::MachineInstr* instr1 = pop1.machineInstr();
    const llvm::MachineInstr* instr2 = pop2.machineInstr();    
 
    llvm::MachineInstr::mmo_iterator begin1 =
        instr1->memoperands_begin();
    // Machine instruction could in theory have several memory operands.
    // In practice it is usually just one.
    MemoryAliasAnalyzer::AliasingResult result = ALIAS_UNKNOWN;
    while (begin1 != instr1->memoperands_end()) {
        const llvm::Value* val1 = (*begin1)->getValue();        
        uint64_t size1 = (*begin1)->getSize();
        llvm::MachineInstr::mmo_iterator begin2 =
            instr2->memoperands_begin();        
            
        while (begin2 != instr2->memoperands_end()) {
            const llvm::Value* val2 = (*begin2)->getValue();
            uint64_t size2 = (*begin2)->getSize();
            if (val1 && val2) {
            
                AliasResult res = 
                    AA_->alias(val1, size1, val2, size2);
                    
                if (res == MayAlias || res == PartialAlias) {
                    result = ALIAS_UNKNOWN;
                }
                if (res == MustAlias) {
                    result = ALIAS_TRUE;
                }
                if (res == NoAlias) {
                    result = ALIAS_FALSE;
                }
            } else {
                result = ALIAS_UNKNOWN;
            }
            begin2++;
        }
        begin1++;
    }
    return result;
}
 
/**
 * Sets active Alias Analyzer picked from LLVM.
 */
void
LLVMAliasAnalyzer::setLLVMAA(llvm::AliasAnalysis* AA) {
    AA_ = AA;
}
 
LLVMAliasAnalyzer::~LLVMAliasAnalyzer() {}