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131 lines
3.9 KiB
C++
131 lines
3.9 KiB
C++
// -*- mode: C++; c-file-style: "cc-mode" -*-
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//*************************************************************************
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// DESCRIPTION: Verilator: Branch prediction
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//
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// Code available from: https://verilator.org
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//
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//*************************************************************************
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//
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// Copyright 2003-2020 by Wilson Snyder. This program is free software; you
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// can redistribute it and/or modify it under the terms of either the GNU
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// Lesser General Public License Version 3 or the Perl Artistic License
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// Version 2.0.
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// SPDX-License-Identifier: LGPL-3.0-only OR Artistic-2.0
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//
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//*************************************************************************
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// BRANCH TRANSFORMATIONS:
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// At each IF/(IF else).
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// Count underneath $display/$stop statements.
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// If more on if than else, this branch is unlikely, or vice-versa.
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// At each FTASKREF,
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// Count calls into the function
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// Then, if FTASK is called only once, add inline attribute
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//
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//*************************************************************************
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#include "config_build.h"
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#include "verilatedos.h"
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#include "V3Global.h"
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#include "V3Branch.h"
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#include "V3Ast.h"
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#include <map>
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//######################################################################
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// Branch state, as a visitor of each AstNode
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class BranchVisitor final : public AstNVisitor {
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private:
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// NODE STATE
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// Entire netlist:
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// AstFTask::user1() -> int. Number of references
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AstUser1InUse m_inuser1;
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// TYPES
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typedef std::vector<AstCFunc*> CFuncVec;
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// STATE
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int m_likely; // Excuses for branch likely taken
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int m_unlikely; // Excuses for branch likely not taken
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CFuncVec m_cfuncsp; // List of all tasks
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// METHODS
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VL_DEBUG_FUNC; // Declare debug()
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void reset() {
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m_likely = false;
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m_unlikely = false;
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}
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void checkUnlikely(AstNode* nodep) {
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if (nodep->isUnlikely()) {
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UINFO(4, " UNLIKELY: " << nodep << endl);
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m_unlikely++;
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}
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}
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// VISITORS
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virtual void visit(AstNodeIf* nodep) override {
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UINFO(4, " IF: " << nodep << endl);
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VL_RESTORER(m_likely);
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VL_RESTORER(m_unlikely);
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{
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// Do if
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reset();
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iterateAndNextNull(nodep->ifsp());
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int ifLikely = m_likely;
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int ifUnlikely = m_unlikely;
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// Do else
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reset();
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iterateAndNextNull(nodep->elsesp());
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int elseLikely = m_likely;
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int elseUnlikely = m_unlikely;
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// Compute
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int likeness = ifLikely - ifUnlikely - (elseLikely - elseUnlikely);
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if (likeness > 0) {
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nodep->branchPred(VBranchPred::BP_LIKELY);
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} else if (likeness < 0) {
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nodep->branchPred(VBranchPred::BP_UNLIKELY);
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} // else leave unknown
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}
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}
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virtual void visit(AstNodeCCall* nodep) override {
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checkUnlikely(nodep);
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nodep->funcp()->user1Inc();
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iterateChildren(nodep);
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}
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virtual void visit(AstCFunc* nodep) override {
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checkUnlikely(nodep);
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m_cfuncsp.push_back(nodep);
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iterateChildren(nodep);
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}
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virtual void visit(AstNode* nodep) override {
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checkUnlikely(nodep);
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iterateChildren(nodep);
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}
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// METHODS
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void calc_tasks() {
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for (AstCFunc* nodep : m_cfuncsp) {
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if (!nodep->dontInline()) nodep->isInline(true);
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}
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}
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public:
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// CONSTRUCTORS
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explicit BranchVisitor(AstNetlist* nodep) {
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reset();
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iterateChildren(nodep);
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calc_tasks();
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}
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virtual ~BranchVisitor() override = default;
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};
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//######################################################################
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// Branch class functions
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void V3Branch::branchAll(AstNetlist* nodep) {
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UINFO(2, __FUNCTION__ << ": " << endl);
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BranchVisitor visitor(nodep);
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}
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