forked from github/verilator
106 lines
3.0 KiB
C++
106 lines
3.0 KiB
C++
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// $Id$
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//*************************************************************************
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// DESCRIPTION: Verilator: Branch prediction
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//
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// Code available from: http://www.veripool.com/verilator
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//
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// AUTHORS: Wilson Snyder with Paul Wasson, Duane Gabli
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//
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//*************************************************************************
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//
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// Copyright 2003-2006 by Wilson Snyder. This program is free software; you can
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// redistribute it and/or modify it under the terms of either the GNU
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// General Public License or the Perl Artistic License.
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//
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// Verilator is distributed in the hope that it will be useful,
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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// GNU General Public License for more details.
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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 then else, this branch is unlikely, or vice-versa.
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//
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//*************************************************************************
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#include "config.h"
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#include <stdio.h>
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#include <stdarg.h>
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#include <unistd.h>
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#include <map>
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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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//######################################################################
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// Branch state, as a visitor of each AstNode
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class BranchVisitor : public AstNVisitor {
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private:
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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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//int debug() { return 9; }
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// METHODS
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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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// VISITORS
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virtual void visit(AstNodeIf* nodep, AstNUser*) {
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UINFO(4," IF: "<<nodep<<endl);
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int lastLikely = m_likely;
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int lastUnlikely = m_unlikely;
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{
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// Do if
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reset();
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nodep->ifsp()->iterateAndNext(*this);
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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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nodep->elsesp()->iterateAndNext(*this);
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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(AstBranchPred::LIKELY);
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} else if (likeness<0) {
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nodep->branchPred(AstBranchPred::UNLIKELY);
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} // else leave unknown
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}
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m_likely = lastLikely;
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m_unlikely = lastUnlikely;
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}
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virtual void visit(AstNode* nodep, AstNUser*) {
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// Default: Just iterate
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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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nodep->iterateChildren(*this);
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}
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public:
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// CONSTUCTORS
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BranchVisitor(AstNetlist* rootp) {
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reset();
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rootp->iterateChildren(*this);
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}
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virtual ~BranchVisitor() {}
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};
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//######################################################################
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// Branch class functions
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void V3Branch::branchAll(AstNetlist* rootp) {
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UINFO(2,__FUNCTION__<<": "<<endl);
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BranchVisitor visitor (rootp);
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}
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