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492 lines
18 KiB
C++
492 lines
18 KiB
C++
// -*- mode: C++; c-file-style: "cc-mode" -*-
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//*************************************************************************
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// DESCRIPTION: Verilator: Break case statements up and add Unknown assigns
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//
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// Code available from: http://www.veripool.org/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 2003-2012 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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// Lesser General Public License Version 3 or the Perl Artistic License
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// Version 2.0.
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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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// V3Case's Transformations:
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//
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// Each module:
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// TBD: Eliminate tristates by adding __in, __inen, __en wires in parallel
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// Need __en in changed list if a signal is on the LHS of a assign
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// Cases:
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// CASE(v) CASEITEM(items,body) -> IF (OR (EQ (AND v mask)
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// (AND item1 mask))
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// (other items))
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// body
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// Or, converts to a if/else tree.
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// FUTURES:
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// Large 16+ bit tables with constants and no masking (address muxes)
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// Enter all into multimap, sort by value and use a tree of < and == compares.
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// "Diagonal" find of {rightmost,leftmost} bit {set,clear}
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// Ignoring mask, check each value is unique (using multimap as above?)
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// Each branch is then mask-and-compare operation (IE <000000001_000000000 at midpoint.)
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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 <cstdio>
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#include <cstdarg>
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#include <unistd.h>
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#include <algorithm>
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#include "V3Global.h"
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#include "V3Case.h"
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#include "V3Ast.h"
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#include "V3Stats.h"
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#define CASE_OVERLAP_WIDTH 12 // Maximum width we can check for overlaps in
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#define CASE_BARF 999999 // Magic width when non-constant
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#define CASE_ENCODER_GROUP_DEPTH 8 // Levels of priority to be ORed together in top IF tree
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//######################################################################
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class CaseLintVisitor : public AstNVisitor {
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private:
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AstNodeCase* m_caseExprp; // Under a CASE value node, if so the relevant case statement
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static int debug() {
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static int level = -1;
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if (VL_UNLIKELY(level < 0)) level = v3Global.opt.debugSrcLevel(__FILE__);
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return level;
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}
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virtual void visit(AstNodeCase* nodep, AstNUser*) {
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if (nodep->castCase() && nodep->castCase()->casex()) {
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nodep->v3warn(CASEX,"Suggest casez (with ?'s) in place of casex (with X's)");
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}
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// Detect multiple defaults
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bool hitDefault = false;
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for (AstCaseItem* itemp = nodep->itemsp(); itemp; itemp=itemp->nextp()->castCaseItem()) {
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if (itemp->isDefault()) {
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if (hitDefault) {
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nodep->v3error("Multiple default statements in case statement.");
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}
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hitDefault = true;
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}
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}
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// Check for X/Z in non-casex statements
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{
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m_caseExprp = nodep;
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nodep->exprp()->accept(*this);
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for (AstCaseItem* itemp = nodep->itemsp(); itemp; itemp=itemp->nextp()->castCaseItem()) {
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itemp->condsp()->iterateAndNext(*this);
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}
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m_caseExprp = NULL;
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}
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}
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virtual void visit(AstConst* nodep, AstNUser*) {
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// See also neverItem
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if (m_caseExprp && nodep->num().isFourState()) {
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if (m_caseExprp->castGenCase()) {
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nodep->v3error("Use of x/? constant in generate case statement, (no such thing as 'generate casez')");
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} else if (m_caseExprp->castCase() && m_caseExprp->castCase()->casex()) {
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// Don't sweat it, we already complained about casex in general
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} else if (m_caseExprp->castCase() && m_caseExprp->castCase()->casez()) {
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if (nodep->num().isUnknown()) {
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nodep->v3warn(CASEWITHX, "Use of x constant in casez statement, (perhaps intended ?/z in constant)");
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}
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} else {
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nodep->v3warn(CASEWITHX, "Use of x/? constant in case statement, (perhaps intended casex/casez)");
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}
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}
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}
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virtual void visit(AstNode* nodep, AstNUser*) {
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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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CaseLintVisitor(AstNodeCase* nodep) {
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m_caseExprp = NULL;
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nodep->accept(*this);
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}
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virtual ~CaseLintVisitor() {}
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};
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//######################################################################
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// Case state, as a visitor of each AstNode
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class CaseVisitor : public AstNVisitor {
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private:
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// NODE STATE
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// Cleared each Case
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// AstIf::user3() -> bool. Set true to indicate clone not needed
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AstUser3InUse m_inuser3;
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// STATE
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V3Double0 m_statCaseFast; // Statistic tracking
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V3Double0 m_statCaseSlow; // Statistic tracking
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// Per-CASE
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int m_caseWidth; // Width of valueItems
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int m_caseItems; // Number of caseItem unique values
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bool m_caseNoOverlapsAllCovered; // Proven to be synopsys parallel_case compliant
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AstNode* m_valueItem[1<<CASE_OVERLAP_WIDTH]; // For each possible value, the case branch we need
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// METHODS
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static int debug() {
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static int level = -1;
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if (VL_UNLIKELY(level < 0)) level = v3Global.opt.debugSrcLevel(__FILE__);
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return level;
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}
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bool isCaseTreeFast(AstCase* nodep) {
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int width = 0;
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bool opaque = false;
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m_caseItems = 0;
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m_caseNoOverlapsAllCovered = true;
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for (AstCaseItem* itemp = nodep->itemsp(); itemp; itemp=itemp->nextp()->castCaseItem()) {
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for (AstNode* icondp = itemp->condsp(); icondp!=NULL; icondp=icondp->nextp()) {
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if (icondp->width() > width) width = icondp->width();
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if (icondp->isDouble()) opaque = true;
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if (!icondp->castConst()) width = CASE_BARF; // Can't parse; not a constant
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m_caseItems++;
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}
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}
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m_caseWidth = width;
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if (width==0 || width > CASE_OVERLAP_WIDTH || opaque) {
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m_caseNoOverlapsAllCovered = false;
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return false; // Too wide for analysis
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}
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UINFO(8,"Simple case statement: "<<nodep<<endl);
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// Zero list of items for each value
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for (uint32_t i=0; i<(1UL<<m_caseWidth); i++) m_valueItem[i] = NULL;
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// Now pick up the values for each assignment
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// We can cheat and use uint32_t's because we only support narrow case's
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bool bitched = false;
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for (AstCaseItem* itemp = nodep->itemsp(); itemp; itemp=itemp->nextp()->castCaseItem()) {
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for (AstNode* icondp = itemp->condsp(); icondp!=NULL; icondp=icondp->nextp()) {
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//if (debug()>=9) icondp->dumpTree(cout," caseitem: ");
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AstConst* iconstp = icondp->castConst();
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if (!iconstp) nodep->v3fatalSrc("above 'can't parse' should have caught this\n");
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if (neverItem(nodep, iconstp)) {
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// X in casez can't ever be executed
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} else {
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V3Number nummask (itemp->fileline(), iconstp->width());
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nummask.opBitsNonX(iconstp->num());
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uint32_t mask = nummask.toUInt();
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V3Number numval (itemp->fileline(), iconstp->width());
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numval.opBitsOne(iconstp->num());
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uint32_t val = numval.toUInt();
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for (uint32_t i=0; i<(1UL<<m_caseWidth); i++) {
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if ((i & mask) == val) {
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if (!m_valueItem[i]) {
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m_valueItem[i] = itemp;
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} else if (!itemp->ignoreOverlap() && !bitched) {
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itemp->v3warn(CASEOVERLAP,"Case values overlap (example pattern 0x"<<hex<<i<<")");
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bitched = true;
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m_caseNoOverlapsAllCovered = false;
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}
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}
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}
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}
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}
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// Defaults were moved to last in the caseitem list by V3Link
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if (itemp->isDefault()) { // Case statement's default... Fill the table
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for (uint32_t i=0; i<(1UL<<m_caseWidth); i++) {
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if (!m_valueItem[i]) m_valueItem[i] = itemp;
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}
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}
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}
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for (uint32_t i=0; i<(1UL<<m_caseWidth); i++) {
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if (!m_valueItem[i]) {
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nodep->v3warn(CASEINCOMPLETE,"Case values incompletely covered (example pattern 0x"<<hex<<i<<")");
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m_caseNoOverlapsAllCovered = false;
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return false;
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}
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}
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if (m_caseItems <= 3) return false; // Not worth simplifing
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// Convert valueItem from AstCaseItem* to the expression
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// Not done earlier, as we may now have a NULL because it's just a ";" NOP branch
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for (uint32_t i=0; i<(1UL<<m_caseWidth); i++) {
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m_valueItem[i] = m_valueItem[i]->castCaseItem()->bodysp();
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}
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return true; // All is fine
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}
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AstNode* replaceCaseFastRecurse(AstNode* cexprp, int msb, uint32_t upperValue) {
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if (msb<0) {
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// There's no space for a IF. We know upperValue is thus down to a specific
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// exact value, so just return the tree value
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// Note can't clone here, as we're going to check for equivelence above
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return m_valueItem[upperValue];
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}
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else {
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// Make left and right subtrees
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// cexpr[msb:lsb] == 1
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AstNode* tree0p = replaceCaseFastRecurse(cexprp, msb-1, upperValue | 0);
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AstNode* tree1p = replaceCaseFastRecurse(cexprp, msb-1, upperValue | (1UL<<msb));
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if (tree0p == tree1p) {
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// Same logic on both sides, so we can just return one of 'em
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return tree0p;
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}
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// We could have a "checkerboard" with A B A B, we can use the same IF on both edges
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bool same = true;
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for (uint32_t a=upperValue,
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b=(upperValue|(1UL<<msb));
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a < (upperValue|(1UL<<msb));
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a++, b++) {
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if (m_valueItem[a] != m_valueItem[b]) { same=false; break; }
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}
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if (same) {
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tree1p->deleteTree(); tree1p=NULL;
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return tree0p;
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}
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// Must have differing logic, so make a selection
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// Case expressions can't be linked twice, so clone them
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if (tree0p && !tree0p->user3()) tree0p = tree0p->cloneTree(true);
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if (tree1p && !tree1p->user3()) tree1p = tree1p->cloneTree(true);
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// Alternate scheme if we ever do multiple bits at a time:
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//V3Number nummask (cexprp->fileline(), cexprp->width(), (1UL<<msb));
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//AstNode* and1p = new AstAnd(cexprp->fileline(), cexprp->cloneTree(false),
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// new AstConst(cexprp->fileline(), nummask));
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AstNode* and1p = new AstSel(cexprp->fileline(), cexprp->cloneTree(false),
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msb, 1);
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AstNode* eqp = new AstNeq(cexprp->fileline(),
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new AstConst(cexprp->fileline(), 0),
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and1p);
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AstIf* ifp = new AstIf(cexprp->fileline(), eqp, tree1p, tree0p);
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ifp->user3(1); // So we don't bother to clone it
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return ifp;
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}
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}
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void replaceCaseFast(AstCase* nodep) {
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// CASEx(cexpr,....
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// -> tree of IF(msb, IF(msb-1, 11, 10)
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// IF(msb-1, 01, 00))
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AstNode* cexprp = nodep->exprp()->unlinkFrBack();
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if (debug()>=9) {
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for (uint32_t i=0; i<(1UL<<m_caseWidth); i++) {
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if (AstNode* itemp = m_valueItem[i]) {
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UINFO(9,"Value "<<hex<<i<<" "<<itemp<<endl);
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}
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}
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}
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// Handle any assertions
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replaceCaseParallel(nodep, m_caseNoOverlapsAllCovered);
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AstNode::user3ClearTree();
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AstNode* ifrootp = replaceCaseFastRecurse(cexprp, m_caseWidth-1, 0UL);
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// Case expressions can't be linked twice, so clone them
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if (ifrootp && !ifrootp->user3()) ifrootp = ifrootp->cloneTree(true);
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if (ifrootp) nodep->replaceWith(ifrootp);
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else nodep->unlinkFrBack();
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nodep->deleteTree(); nodep=NULL;
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cexprp->deleteTree(); cexprp=NULL;
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if (debug()>=9) ifrootp->dumpTree(cout," _simp: ");
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}
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void replaceCaseComplicated(AstCase* nodep) {
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// CASEx(cexpr,ITEM(icond1,istmts1),ITEM(icond2,istmts2),ITEM(default,istmts3))
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// -> IF((cexpr==icond1),istmts1,
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// IF((EQ (AND MASK cexpr) (AND MASK icond1)
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// ,istmts2, istmts3
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AstNode* cexprp = nodep->exprp()->unlinkFrBack();
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// We'll do this in two stages. First stage, convert the conditions to
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// the appropriate IF AND terms.
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if (debug()>=9) nodep->dumpTree(cout," _comp_IN: ");
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bool hadDefault = false;
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for (AstCaseItem* itemp = nodep->itemsp(); itemp; itemp=itemp->nextp()->castCaseItem()) {
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if (!itemp->condsp()) {
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// Default clause. Just make true, we'll optimize it away later
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itemp->condsp(new AstConst(itemp->fileline(), AstConst::LogicTrue()));
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hadDefault = true;
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} else {
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// Expressioned clause
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AstNode* icondNextp = NULL;
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AstNode* ifexprp = NULL; // If expression to test
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for (AstNode* icondp = itemp->condsp(); icondp!=NULL; icondp=icondNextp) {
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icondNextp = icondp->nextp();
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icondp->unlinkFrBack();
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AstNode* and1p;
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AstNode* and2p;
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AstConst* iconstp = icondp->castConst();
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if (iconstp && neverItem(nodep, iconstp)) {
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// X in casez can't ever be executed
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icondp->deleteTree(); icondp=NULL; iconstp=NULL;
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// For simplicity, make expression that is not equal, and let later
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// optimizations remove it
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and1p = new AstConst(itemp->fileline(), AstConst::LogicFalse());
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and2p = new AstConst(itemp->fileline(), AstConst::LogicTrue());
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} else if (iconstp && iconstp->num().isFourState()
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&& (nodep->casex() || nodep->casez())) {
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V3Number nummask (itemp->fileline(), iconstp->width());
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nummask.opBitsNonX(iconstp->num());
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V3Number numval (itemp->fileline(), iconstp->width());
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numval.opBitsOne(iconstp->num());
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and1p = new AstAnd(itemp->fileline(), cexprp->cloneTree(false),
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new AstConst(itemp->fileline(), nummask));
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and2p = new AstAnd(itemp->fileline(),
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new AstConst(itemp->fileline(), numval),
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new AstConst(itemp->fileline(), nummask));
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icondp->deleteTree(); icondp=NULL; iconstp=NULL;
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} else {
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// Not a caseX mask, we can simply build CASEEQ(cexpr icond)
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and1p = cexprp->cloneTree(false);
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and2p = icondp;
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}
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AstNodeBiop* condp = (and1p->isDouble()
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? (new AstEqD(itemp->fileline(), and1p, and2p))->castNodeBiop()
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: (new AstEq(itemp->fileline(), and1p, and2p))->castNodeBiop());
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if (!ifexprp) {
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ifexprp = condp;
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} else {
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ifexprp = new AstLogOr(itemp->fileline(), ifexprp, condp);
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}
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}
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// Replace expression in tree
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itemp->condsp(ifexprp);
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}
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}
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cexprp->deleteTree(); cexprp=NULL;
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if (!hadDefault) {
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// If there was no default, add a empty one, this greatly simplifies below code
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// and constant propagation will just eliminate it for us later.
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nodep->addItemsp(new AstCaseItem(nodep->fileline(),
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new AstConst(nodep->fileline(), AstConst::LogicTrue()),
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NULL));
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}
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if (debug()>=9) nodep->dumpTree(cout," _comp_COND: ");
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// Now build the IF statement tree
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// The tree can be quite huge. Pull ever group of 8 out, and make a OR tree.
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// This reduces the depth for the bottom elements, at the cost of some of the top elements.
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// If we ever have profiling data, we should pull out the most common item from here and
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// instead make it the first IF branch.
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int depth = 0;
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AstNode* grouprootp = NULL;
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AstIf* groupnextp = NULL;
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AstIf* itemnextp = NULL;
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for (AstCaseItem* itemp = nodep->itemsp(); itemp; itemp=itemp->nextp()->castCaseItem()) {
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AstNode* istmtsp = itemp->bodysp(); // Maybe null -- no action.
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if (istmtsp) istmtsp->unlinkFrBackWithNext();
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// Expressioned clause
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AstNode* ifexprp = itemp->condsp()->unlinkFrBack();
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{ // Prepare for next group
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if (++depth > CASE_ENCODER_GROUP_DEPTH) depth = 1;
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if (depth == 1) { // First group or starting new group
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itemnextp = NULL;
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AstIf* newp = new AstIf(itemp->fileline(), ifexprp->cloneTree(true), NULL, NULL);
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if (groupnextp) groupnextp->addElsesp(newp);
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else grouprootp = newp;
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groupnextp = newp;
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} else { // Continue group, modify if condition to OR in this new condition
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AstNode* condp = groupnextp->condp()->unlinkFrBack();
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groupnextp->condp(new AstOr(ifexprp->fileline(),
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condp,
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ifexprp->cloneTree(true)));
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}
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}
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{ // Make the new lower IF and attach in the tree
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AstNode* itemexprp = ifexprp; ifexprp=NULL;
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if (depth == (CASE_ENCODER_GROUP_DEPTH)) { // End of group - can skip the condition
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itemexprp->deleteTree(); itemexprp=NULL;
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itemexprp = new AstConst(itemp->fileline(), AstConst::LogicTrue());
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}
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AstIf* newp = new AstIf(itemp->fileline(), itemexprp, istmtsp, NULL);
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if (itemnextp) itemnextp->addElsesp(newp);
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else groupnextp->addIfsp(newp); // First in a new group
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itemnextp = newp;
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}
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}
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if (debug()>=9) nodep->dumpTree(cout," _comp_TREE: ");
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// Handle any assertions
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replaceCaseParallel(nodep, false);
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// Replace the CASE... with IF...
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if (debug()>=9) grouprootp->dumpTree(cout," _new: ");
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if (grouprootp) nodep->replaceWith(grouprootp);
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else nodep->unlinkFrBack();
|
||
nodep->deleteTree(); nodep=NULL;
|
||
}
|
||
|
||
void replaceCaseParallel(AstCase* nodep, bool noOverlapsAllCovered) {
|
||
// Take the notParallelp tree under the case statement created by V3Assert
|
||
// If the statement was proven to have no overlaps and all cases covered, we're done with it.
|
||
// Else, convert to a normal statement parallel with the case statement.
|
||
if (nodep->notParallelp() && !noOverlapsAllCovered) {
|
||
AstNode* parp = nodep->notParallelp()->unlinkFrBackWithNext();
|
||
nodep->addNextHere(parp);
|
||
}
|
||
}
|
||
|
||
bool neverItem(AstCase* casep, AstConst* itemp) {
|
||
// Xs in case or casez are impossible due to two state simulations
|
||
if (casep->casex()) {
|
||
} else if (casep->casez()) {
|
||
if (itemp->num().isUnknown()) return true;
|
||
} else {
|
||
if (itemp->num().isFourState()) return true;
|
||
}
|
||
return false;
|
||
}
|
||
|
||
// VISITORS
|
||
virtual void visit(AstCase* nodep, AstNUser*) {
|
||
V3Case::caseLint(nodep);
|
||
nodep->iterateChildren(*this);
|
||
if (debug()>=9) nodep->dumpTree(cout," case_old: ");
|
||
if (isCaseTreeFast(nodep) && v3Global.opt.oCase()) {
|
||
// It's a simple priority encoder or complete statement
|
||
// we can make a tree of statements to avoid extra comparisons
|
||
++m_statCaseFast;
|
||
replaceCaseFast(nodep); nodep=NULL;
|
||
} else {
|
||
++m_statCaseSlow;
|
||
replaceCaseComplicated(nodep); nodep=NULL;
|
||
}
|
||
}
|
||
//--------------------
|
||
// Default: Just iterate
|
||
virtual void visit(AstNode* nodep, AstNUser*) {
|
||
nodep->iterateChildren(*this);
|
||
}
|
||
|
||
public:
|
||
// CONSTUCTORS
|
||
CaseVisitor(AstNetlist* nodep) {
|
||
m_caseNoOverlapsAllCovered = false;
|
||
nodep->accept(*this);
|
||
}
|
||
virtual ~CaseVisitor() {
|
||
V3Stats::addStat("Optimizations, Cases parallelized", m_statCaseFast);
|
||
V3Stats::addStat("Optimizations, Cases complex", m_statCaseSlow);
|
||
}
|
||
};
|
||
|
||
//######################################################################
|
||
// Case class functions
|
||
|
||
void V3Case::caseAll(AstNetlist* nodep) {
|
||
UINFO(2,__FUNCTION__<<": "<<endl);
|
||
CaseVisitor visitor (nodep);
|
||
}
|
||
void V3Case::caseLint(AstNodeCase* nodep) {
|
||
UINFO(4,__FUNCTION__<<": "<<endl);
|
||
CaseLintVisitor visitor (nodep);
|
||
}
|