81 lines
2.7 KiB
C++
81 lines
2.7 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 2003-2025 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 "V3PchAstNoMT.h" // VL_MT_DISABLED_CODE_UNIT
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#include "V3Branch.h"
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VL_DEFINE_DEBUG_FUNCTIONS;
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//######################################################################
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// Branch state, as a visitor of each AstNode
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class BranchVisitor final : public VNVisitorConst {
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// STATE - for current visit position (use VL_RESTORER)
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int m_unlikely = 0; // Excuses for branch likely not taken
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// VISITORS
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void visit(AstNodeIf* nodep) override {
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UINFO(4, " IF: " << nodep);
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VL_RESTORER(m_unlikely);
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// Do then
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m_unlikely = 0;
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iterateAndNextConstNull(nodep->thensp());
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const int thenUnlikely = m_unlikely;
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// Do else
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m_unlikely = 0;
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iterateAndNextConstNull(nodep->elsesp());
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const int elseUnlikely = m_unlikely;
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// Compute
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if (elseUnlikely > thenUnlikely) {
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nodep->branchPred(VBranchPred::BP_LIKELY);
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} else if (elseUnlikely < thenUnlikely) {
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nodep->branchPred(VBranchPred::BP_UNLIKELY);
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} // else leave unknown
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}
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void visit(AstNode* nodep) override {
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if (nodep->isUnlikely()) {
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UINFO(4, " UNLIKELY: " << nodep);
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++m_unlikely;
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}
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iterateChildrenConst(nodep);
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}
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public:
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// CONSTRUCTORS
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explicit BranchVisitor(AstNetlist* nodep) { iterateChildrenConst(nodep); }
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~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__ << ":");
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{ BranchVisitor{nodep}; }
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V3Global::dumpCheckGlobalTree("branch", 0, dumpTreeEitherLevel() >= 3);
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}
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