verilator/src/V3Cast.cpp

// -*- mode: C++; c-file-style: "cc-mode" -*-
//*************************************************************************
// DESCRIPTION: Verilator: Add C++ casts across expression size changes
//
// Code available from: https://verilator.org
//
//*************************************************************************
//
// Copyright 2004-2021 by Wilson Snyder. This program is free software; you
// can redistribute it and/or modify it under the terms of either the GNU
// Lesser General Public License Version 3 or the Perl Artistic License
// Version 2.0.
// SPDX-License-Identifier: LGPL-3.0-only OR Artistic-2.0
//
//*************************************************************************
// V3Cast's Transformations:
//
// Each module:
//      For each math operator, if above operator requires 32 bits,
//      and this isn't, cast to 32 bits.
//      Likewise for 64 bit operators.
//
// C++ rules:
//      Integral promotions allow conversion to larger int.  Unsigned is only
//      used if a int would not fit the value.
//
//      Bools converts to int, not unsigned.
//
//      Most operations return unsigned if either operand is unsigned.
//
//      Unsignedness can be lost on results of the below operations, as they
//      may need the sign bit for proper operation:
//              /, %, /=, %=, <, <=, >, or >=
//
//      Signed values are always sign extended on promotion or right shift,
//      even if assigning to a unsigned.
//
//*************************************************************************

#include "config_build.h"
#include "verilatedos.h"

#include "V3Global.h"
#include "V3Cast.h"
#include "V3Ast.h"

#include <algorithm>

//######################################################################
// Cast state, as a visitor of each AstNode

class CastVisitor final : public AstNVisitor {
private:
    // NODE STATE
    // Entire netlist:
    //   AstNode::user()                // bool.  Indicates node is of known size
    const AstUser1InUse m_inuser1;

    // STATE

    // METHODS
    VL_DEBUG_FUNC;  // Declare debug()

    void insertCast(AstNode* nodep, int needsize) {  // We'll insert ABOVE passed node
        UINFO(4, "  NeedCast " << nodep << endl);
        AstNRelinker relinkHandle;
        nodep->unlinkFrBack(&relinkHandle);
        //
        AstCCast* const castp
            = new AstCCast{nodep->fileline(), nodep, needsize, nodep->widthMin()};
        relinkHandle.relink(castp);
        // if (debug() > 8) castp->dumpTree(cout, "-castins: ");
        //
        ensureLower32Cast(castp);
        nodep->user1(1);  // Now must be of known size
    }
    static int castSize(AstNode* nodep) {
        if (nodep->isQuad()) {
            return VL_QUADSIZE;
        } else if (nodep->width() <= 8) {
            return 8;
        } else if (nodep->width() <= 16) {
            return 16;
        } else {
            return VL_IDATASIZE;
        }
    }
    void ensureCast(AstNode* nodep) {
        if (castSize(nodep->backp()) != castSize(nodep) || !nodep->user1()) {
            insertCast(nodep, castSize(nodep->backp()));
        }
    }
    void ensureLower32Cast(AstCCast* nodep) {
        // If we have uint64 = CAST(uint64(x)) then the upcasting
        // really needs to be CAST(uint64(CAST(uint32(x))).
        // Otherwise a (uint64)(a>b) would return wrong value, as
        // less than has nondeterministic signedness.
        if (nodep->isQuad() && !nodep->lhsp()->isQuad() && !VN_IS(nodep->lhsp(), CCast)) {
            insertCast(nodep->lhsp(), VL_IDATASIZE);
        }
    }
    void ensureNullChecked(AstNode* nodep) {
        // TODO optimize to track null checked values and avoid where possible
        if (!VN_IS(nodep->backp(), NullCheck)) {
            AstNRelinker relinkHandle;
            nodep->unlinkFrBack(&relinkHandle);
            AstNode* const newp = new AstNullCheck{nodep->fileline(), nodep};
            relinkHandle.relink(newp);
        }
    }

    // VISITORS
    virtual void visit(AstNodeUniop* nodep) override {
        iterateChildren(nodep);
        nodep->user1(nodep->lhsp()->user1());
        if (nodep->sizeMattersLhs()) ensureCast(nodep->lhsp());
    }
    virtual void visit(AstNodeBiop* nodep) override {
        iterateChildren(nodep);
        nodep->user1(nodep->lhsp()->user1() | nodep->rhsp()->user1());
        if (nodep->sizeMattersLhs()) ensureCast(nodep->lhsp());
        if (nodep->sizeMattersRhs()) ensureCast(nodep->rhsp());
    }
    virtual void visit(AstNodeTriop* nodep) override {
        iterateChildren(nodep);
        nodep->user1(nodep->lhsp()->user1() | nodep->rhsp()->user1() | nodep->thsp()->user1());
        if (nodep->sizeMattersLhs()) ensureCast(nodep->lhsp());
        if (nodep->sizeMattersRhs()) ensureCast(nodep->rhsp());
        if (nodep->sizeMattersThs()) ensureCast(nodep->thsp());
    }
    virtual void visit(AstNodeQuadop* nodep) override {
        iterateChildren(nodep);
        nodep->user1(nodep->lhsp()->user1() | nodep->rhsp()->user1() | nodep->thsp()->user1()
                     | nodep->fhsp()->user1());
        if (nodep->sizeMattersLhs()) ensureCast(nodep->lhsp());
        if (nodep->sizeMattersRhs()) ensureCast(nodep->rhsp());
        if (nodep->sizeMattersThs()) ensureCast(nodep->thsp());
        if (nodep->sizeMattersFhs()) ensureCast(nodep->fhsp());
    }
    virtual void visit(AstCCast* nodep) override {
        iterateChildren(nodep);
        ensureLower32Cast(nodep);
        nodep->user1(1);
    }
    virtual void visit(AstNegate* nodep) override {
        iterateChildren(nodep);
        nodep->user1(nodep->lhsp()->user1());
        if (nodep->lhsp()->widthMin() == 1) {
            // We want to avoid a GCC "converting of negative value" warning
            // from our expansion of
            //    out = {32{a<b}}  =>   out = - (a<b)
            insertCast(nodep->lhsp(), castSize(nodep));
        } else {
            ensureCast(nodep->lhsp());
        }
    }
    virtual void visit(AstVarRef* nodep) override {
        const AstNode* const backp = nodep->backp();
        if (nodep->access().isReadOnly() && !VN_IS(backp, CCast) && VN_IS(backp, NodeMath)
            && !VN_IS(backp, ArraySel) && !VN_IS(backp, RedXor) && backp->width()
            && castSize(nodep) != castSize(nodep->varp())) {
            // Cast vars to IData first, else below has upper bits wrongly set
            //  CData x=3; out = (QData)(x<<30);
            insertCast(nodep, castSize(nodep));
        }
        nodep->user1(1);
    }
    virtual void visit(AstConst* nodep) override {
        // Constants are of unknown size if smaller than 33 bits, because
        // we're too lazy to wrap every constant in the universe in
        // ((IData)#).
        nodep->user1(nodep->isQuad() || nodep->isWide());
    }

    // Null dereference protection
    virtual void visit(AstNullCheck* nodep) override {
        iterateChildren(nodep);
        nodep->user1(nodep->lhsp()->user1());
    }
    virtual void visit(AstCMethodCall* nodep) override {
        iterateChildren(nodep);
        ensureNullChecked(nodep->fromp());
    }
    virtual void visit(AstMemberSel* nodep) override {
        iterateChildren(nodep);
        ensureNullChecked(nodep->fromp());
    }

    // NOPs
    virtual void visit(AstVar*) override {}

    //--------------------
    virtual void visit(AstNode* nodep) override { iterateChildren(nodep); }

public:
    // CONSTRUCTORS
    explicit CastVisitor(AstNetlist* nodep) { iterate(nodep); }
    virtual ~CastVisitor() override = default;
};

//######################################################################
// Cast class functions

void V3Cast::castAll(AstNetlist* nodep) {
    UINFO(2, __FUNCTION__ << ": " << endl);
    { CastVisitor{nodep}; }  // Destruct before checking
    V3Global::dumpCheckGlobalTree("cast", 0, v3Global.opt.dumpTreeLevel(__FILE__) >= 3);
}