forked from github/verilator
ce10dbd11c
git-svn-id: file://localhost/svn/verilator/trunk/verilator@753 77ca24e4-aefa-0310-84f0-b9a241c72d87
399 lines
14 KiB
C++
399 lines
14 KiB
C++
// $Id$
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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.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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// 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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// Constants:
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// RHS, Replace 5'bx_1_x with a module global we init to a random value
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// CONST(5'bx_1_x) -> VARREF(_{numberedtemp})
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// -> VAR(_{numberedtemp})
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// -> INITIAL(VARREF(_{numberedtemp}), OR(5'bx_1_x,AND(random,5'b0_1_x))
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// OPTIMIZE: Must not collapse this initial back into the equation.
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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 <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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//######################################################################
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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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//int debug() { return 9; }
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virtual void visit(AstNodeCase* nodep, AstNUser*) {
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// We report a syntax error on empty "case (x) endcase" blocks, so never no items at all
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if (!nodep->itemsp()) nodep->v3fatalSrc("No items (not even default) under case statement?\n");
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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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if (!nodep->castCase() || !nodep->castCase()->casex()) {
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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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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 {
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nodep->v3error("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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// 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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int 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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//int debug() { return 9; }
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// METHODS
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bool checkCaseTree(AstCase* nodep) {
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int width = 0;
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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->castConst()) width = 999; // Can't parse; not a constant
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m_caseItems++;
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}
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}
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if (width==0 || width > CASE_OVERLAP_WIDTH) {
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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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m_caseWidth = width;
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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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V3Number nummask (itemp->fileline(), iconstp->width());
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nummask.opBitsNonX(iconstp->num());
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uint32_t mask = nummask.asInt();
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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.asInt();
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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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// Defaults were moved to last in the caseitem list by V3Link
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if (!itemp->condsp()) { // 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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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) return tree0p;
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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();
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cexprp->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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if (ifrootp) nodep->replaceWith(ifrootp);
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else nodep->unlinkFrBack();
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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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AstNode* ifrootp = NULL;
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AstNode* ifnextp = 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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if (!itemp->condsp()) {
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// Default clause. We reordered in link, so default is always last
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if (ifnextp) {
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if (istmtsp) ifnextp->castIf()->addElsesp(istmtsp);
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} else { // Just a empty case default: endcase
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ifnextp = istmtsp;
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}
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if (!ifrootp) ifrootp = istmtsp;
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ifnextp = istmtsp;
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itemp = NULL; break;
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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 && iconstp->num().isFourState()
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&& nodep->casex()) {
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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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} 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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AstEq* condp = new AstEq(itemp->fileline(), and1p, and2p);
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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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// Make the new IF and attach in the tree
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if (ifexprp) {
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AstIf* newp = new AstIf(itemp->fileline(), ifexprp, istmtsp, NULL);
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if (ifnextp) {
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ifnextp->castIf()->addElsesp(newp);
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}
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if (!ifrootp) ifrootp = newp;
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ifnextp = newp;
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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, false);
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// Replace the CASE... with IF...
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if (ifrootp) nodep->replaceWith(ifrootp);
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else nodep->unlinkFrBack();
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if (debug()>=9) ifrootp->dumpTree(cout," _new: ");
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}
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void replaceCaseParallel(AstCase* nodep, bool noOverlapsAllCovered) {
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// Take the notParallelp tree under the case statement created by V3Assert
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// If the statement was proven to have no overlaps and all cases covered, we're done with it.
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// Else, convert to a normal statement parallel with the case statement.
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if (nodep->notParallelp() && !noOverlapsAllCovered) {
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AstNode* parp = nodep->notParallelp()->unlinkFrBackWithNext();
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nodep->addNextHere(parp);
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}
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}
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// VISITORS
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virtual void visit(AstCase* nodep, AstNUser*) {
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V3Case::caseLint(nodep);
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nodep->iterateChildren(*this);
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if (debug()>=9) nodep->dumpTree(cout," case_old: ");
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if (checkCaseTree(nodep) && v3Global.opt.oCase()) {
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// It's a simple priority encoder or complete statement
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// we can make a tree of statements to avoid extra comparisons
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m_statCaseFast++;
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replaceCaseFast(nodep); nodep=NULL;
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} else {
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m_statCaseSlow++;
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replaceCaseComplicated(nodep); nodep=NULL;
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}
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}
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//--------------------
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// Default: Just iterate
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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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CaseVisitor(AstNode* nodep) {
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m_caseNoOverlapsAllCovered = false;
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nodep->accept(*this);
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}
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virtual ~CaseVisitor() {
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V3Stats::addStat("Optimizations, Cases parallelized", m_statCaseFast);
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V3Stats::addStat("Optimizations, Cases priority-encoded", m_statCaseSlow);
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}
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};
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//######################################################################
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// Case class functions
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void V3Case::caseAll(AstNetlist* nodep) {
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UINFO(2,__FUNCTION__<<": "<<endl);
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CaseVisitor visitor (nodep);
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}
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void V3Case::caseLint(AstNodeCase* nodep) {
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UINFO(2,__FUNCTION__<<": "<<endl);
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CaseLintVisitor visitor (nodep);
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}
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