Optimize bit op tree #2186, #2632, and #2633 (#2751)

* Tests:Add some more signals to t_const_opt_red.v * Optimize bit op trees such as ~a[2] & a[1] & ~a[0] to 3'b010 == (3'111 & a) * Update src/V3Const.cpp Co-authored-by: Wilson Snyder <wsnyder@wsnyder.org> * Update src/V3Const.cpp Co-authored-by: Wilson Snyder <wsnyder@wsnyder.org> * Update src/V3Const.cpp Co-authored-by: Wilson Snyder <wsnyder@wsnyder.org> * Apply clang-format * Don't edit and-or tree. * Call matchBitOpTree() after V3Expand does its job. * Internals: Rename newNodep -> newp. No functional change is intended. * Internals: Remove m_sels. No functional change is intended. * Internals: Remove stringstream. No functional change is intended. * Internals: Use V3Number::bitIs1(). No functional change is intended. * Internals: Use V3Number instead of std::map. Resolved laek. Result should be same. * Internals: Resolve overload of setPolarity. No functional change is intended. * Internals: Pass failure reason. No functional change is intended. * Internals: Add VNUser::toPtr(). No functional change is intended. * Internals: Use user4 instead of std::map. No functional change is intended. * Catch up with the AST style aftre V3Expand * Internals: Rename Context to VarInfo. No functional change is intended. * Add some more test case * tests:Add stats to tests Update stats in t_merge_cond.pl as matchBitopTree does some of them. * insert CCast if necessary * small optimization to remove redundant bit mask * No quick exit even when unoptimizable node is found. * Simplify removing redundant And * simplify * Revert "Internals: Add VNUser::toPtr(). No functional change is intended." This reverts commit f98dce10db. * Consider AstWordSel and cleanup * Update test * Update src/V3Const.cpp Co-authored-by: Wilson Snyder <wsnyder@wsnyder.org> * Update src/V3Const.cpp Co-authored-by: Wilson Snyder <wsnyder@wsnyder.org> * Update src/V3Const.cpp Co-authored-by: Wilson Snyder <wsnyder@wsnyder.org> * Update src/V3Const.cpp Co-authored-by: Wilson Snyder <wsnyder@wsnyder.org> * Update src/V3Const.cpp Co-authored-by: Wilson Snyder <wsnyder@wsnyder.org> * Update src/V3Const.cpp Co-authored-by: Wilson Snyder <wsnyder@wsnyder.org> * Apply clang-format * Internals: rename variables. No functional change is intended. Co-authored-by: Wilson Snyder <wsnyder@wsnyder.org> Co-authored-by: github action <action@example.com>
2025-01-06 06:37:45 +00:00 · 2021-02-21 18:11:33 +09:00 · 2021-02-21 18:11:33 +09:00 · bb5384bc50
commit bb5384bc50
parent fd6edd90bc
5 changed files with 474 additions and 7 deletions
--- a/src/V3Const.cpp
+++ b/src/V3Const.cpp
@ -29,9 +29,9 @@
 #include "V3Ast.h"
 #include "V3Width.h"
 #include "V3Simulate.h"
+#include "V3Stats.h"

 #include <algorithm>
-#include <map>

 //######################################################################
 // Utilities
@ -76,6 +76,421 @@ public:
    bool found() const { return m_found; }
 };

+// This visitor can be used in the post-expanded Ast from V3Expand, where the Ast satisfies:
+// - Constants are 64 bit at most (because words are accessed via AstWordSel)
+// - Variables are scoped.
+class ConstBitOpTreeVisitor final : public AstNVisitor {
+    // TYPES
+
+    struct LeafInfo {  // Leaf node (either AstConst or AstVarRef)
+        bool m_polarity = true;
+        int m_lsb = 0;
+        int m_wordIdx = -1;  // -1 means AstWordSel is not used.
+        AstVarRef* m_refp = nullptr;
+        AstConst* m_constp = nullptr;
+    };
+    // Collect information for each Variable to transform as below
+    class VarInfo final {
+        // MEMBERS
+        int m_constResult = -1;  // -1: result is not constant, 0 or 1: result of this tree
+        ConstBitOpTreeVisitor* m_parentp;  // ConstBitOpTreeVisitor that holds this VarInfo
+        AstVarRef* m_refp;  // Points the variable that this VarInfo covers
+        V3Number m_bitPolarity;  // Coefficient of each bit
+        static int widthOfRef(AstVarRef* refp) {
+            if (AstWordSel* selp = VN_CAST(refp->backp(), WordSel)) return selp->width();
+            return refp->width();
+        }
+
+    public:
+        // METHODS
+        bool hasConstantResult() const { return m_constResult >= 0; }
+        void setPolarity(bool compBit, int bit) {
+            UASSERT_OBJ(!hasConstantResult(), m_refp, "Already has result of " << m_constResult);
+            if (m_bitPolarity.bitIsX(bit)) {  // The bit is not yet set
+                m_bitPolarity.setBit(bit, compBit);
+            } else {  // Priviously set the bit
+                const bool sameFlag = m_bitPolarity.bitIs1(bit) == compBit;
+                if (m_parentp->isXorTree()) {
+                    // ^{x[0], ~x[0], x[2], x[3]} === ~^{x[2], x[3]}
+                    UASSERT_OBJ(sameFlag, m_refp, "Only true is set in Xor tree");
+                    m_bitPolarity.setBit(bit, 'x');
+                } else {  // And, Or
+                    // Can ignore this nodep as the bit is already registered
+                    if (sameFlag) return;  // a & a == a, b | b == b
+                    // Otherwise result is constant
+                    m_constResult = m_parentp->isAndTree() ? 0 : 1;
+                    m_bitPolarity.setAllBitsX();  // The variable is not referred anymore
+                }
+            }
+        }
+        AstNode* getResult() const {
+            FileLine* fl = m_refp->fileline();
+            AstNode* srcp = VN_CAST(m_refp->backp(), WordSel);
+            if (!srcp) srcp = m_refp;
+            const int width = widthOfRef(m_refp);
+
+            if (hasConstantResult())
+                return new AstConst{fl,
+                                    V3Number{srcp, width, static_cast<vluint32_t>(m_constResult)}};
+
+            AstConst* maskValuep = new AstConst{fl, V3Number{srcp, width, 0}};
+            maskValuep->num().opBitsNonX(m_bitPolarity);  // 'x' -> 0, 0->1, 1->1
+            // Let AstConst be in lhs as it is the common convention
+            AstAnd* maskedp = new AstAnd{fl, maskValuep, srcp->cloneTree(false)};
+            AstNode* resultp;
+            if (m_parentp->isXorTree()) {
+                resultp = new AstRedXor{fl, maskedp};
+                resultp->dtypep()->widthForce(width, 1);
+            } else {
+                AstConst* compValuep = maskValuep->cloneTree(false);
+                compValuep->num().opBitsOne(m_bitPolarity);  // 'x'->0, 0->0, 1->1
+                if (m_parentp->isAndTree()) {
+                    resultp = new AstEq{fl, compValuep, maskedp};
+                } else {  // Or
+                    compValuep->num().opXor(V3Number{compValuep->num()}, maskValuep->num());
+                    resultp = new AstNeq{fl, compValuep, maskedp};
+                }
+            }
+            return resultp;
+        }
+
+        // CONSTRUCTORS
+        VarInfo(ConstBitOpTreeVisitor* parent, AstVarRef* refp)
+            : m_parentp(parent)
+            , m_refp(refp)
+            , m_bitPolarity(refp, widthOfRef(refp)) {
+            m_bitPolarity.setAllBitsX();
+        }
+    };
+
+    // MEMBERS
+    bool m_failed = false;
+    bool m_polarity = true;  // Flip when AstNot comes
+    int m_ops = 0;  // Number of operations such as And, Or, Xor, Sel...
+    int m_lsb = 0;  // Current LSB
+    LeafInfo* m_leafp = nullptr;  // AstConst or AstVarRef that currently looking for
+    AstNode* m_rootp;  // Root of this AST subtree
+    AstNode* m_curOpp = nullptr;  // The node that should be added to m_frozenNodes
+
+    AstUser4InUse m_inuser4;
+    std::vector<AstNode*> m_frozenNodes;  // Nodes that cannot be optimized
+    std::vector<VarInfo*> m_varInfos;  // VarInfo for each variable, [0] is nullptr
+
+    // NODE STATE
+    // AstVarRef::user4u      -> Base index of m_varInfos that points VarInfo
+    // AstVarScope::user4u    -> Same as AstVarRef::user4
+
+    // METHODS
+    VL_DEBUG_FUNC;  // Declare debug()
+
+    bool isAndTree() const { return VN_IS(m_rootp, And); }
+    bool isOrTree() const { return VN_IS(m_rootp, Or); }
+    bool isXorTree() const { return VN_IS(m_rootp, Xor) || VN_IS(m_rootp, RedXor); }
+
+#define CONST_BITOP_RETURN_IF(cond, nodep) \
+    if (setFailed(cond, #cond, nodep, __LINE__)) return
+
+#define CONST_BITOP_SET_FAILED(reason, nodep) setFailed(true, reason, nodep, __LINE__)
+
+    bool setFailed(bool fail, const char* reason, AstNode* nodep, int line) {
+        if (fail) {
+            UINFO(9, "cannot optimize " << m_rootp << " reason:" << reason << " called from line:"
+                                        << line << " when checking:" << nodep << std::endl);
+            // if (debug() >= 9) m_rootp->dumpTree(std::cout << "Root node:\n");
+        }
+        m_failed |= fail;
+        return m_failed;
+    }
+    void incrOps(const AstNode* nodep, int line) {
+        ++m_ops;
+        UINFO(9, "Increment to " << m_ops << " " << nodep << " called from line " << line << "\n");
+    }
+    VarInfo& getVarInfo(const LeafInfo& ref) {
+        UASSERT_OBJ(ref.m_refp, m_rootp, "null varref in And/Or/Xor optimization");
+        AstNode* nodep = ref.m_refp->varScopep();
+        if (!nodep) nodep = ref.m_refp->varp();  // Not scoped
+        int baseIdx = nodep->user4();
+        if (baseIdx == 0) {  // Not set yet
+            baseIdx = m_varInfos.size();
+            const int numWords
+                = ref.m_refp->dtypep()->isWide() ? ref.m_refp->dtypep()->widthWords() : 1;
+            m_varInfos.resize(m_varInfos.size() + numWords, nullptr);
+            nodep->user4(baseIdx);
+        }
+        const size_t idx = baseIdx + std::max(0, ref.m_wordIdx);
+        VarInfo* varInfop = m_varInfos[idx];
+        if (!varInfop) {
+            varInfop = new VarInfo{this, ref.m_refp};
+            m_varInfos[idx] = varInfop;
+        }
+        return *varInfop;
+    }
+
+    // Traverse down to see AstConst or AstVarRef
+    LeafInfo findLeaf(AstNode* nodep, bool expectConst) {
+        LeafInfo info;
+        {
+            VL_RESTORER(m_leafp);
+            m_leafp = &info;
+            iterate(nodep);
+        }
+
+        bool ok = !m_failed;
+        if (expectConst)
+            ok &= !info.m_refp && info.m_constp;
+        else
+            ok &= info.m_refp && !info.m_constp;
+        return ok ? info : LeafInfo{};
+    }
+    AstNode* combineTree(AstNode* lhsp, AstNode* rhsp) {
+        if (!lhsp) return rhsp;
+        if (isAndTree())
+            return new AstAnd(m_rootp->fileline(), lhsp, rhsp);
+        else if (isOrTree())
+            return new AstOr(m_rootp->fileline(), lhsp, rhsp);
+        else {
+            UASSERT_OBJ(isXorTree(), m_rootp, "must be either Xor or RedXor");
+            return new AstXor(m_rootp->fileline(), lhsp, rhsp);
+        }
+    }
+
+    // VISITORS
+    virtual void visit(AstNode* nodep) override {
+        CONST_BITOP_SET_FAILED("Hit unexpected op", nodep);
+    }
+    virtual void visit(AstCCast* nodep) override { iterateChildren(nodep); }
+    virtual void visit(AstShiftR* nodep) override {
+        CONST_BITOP_RETURN_IF(!m_leafp, nodep);
+        AstConst* constp = VN_CAST(nodep->rhsp(), Const);
+        CONST_BITOP_RETURN_IF(!constp, nodep->rhsp());
+        m_lsb += constp->toUInt();
+        incrOps(nodep, __LINE__);
+        iterate(nodep->lhsp());
+        m_lsb -= constp->toUInt();
+    }
+    virtual void visit(AstNot* nodep) override {
+        CONST_BITOP_RETURN_IF(nodep->widthMin() != 1, nodep);
+        AstNode* lhsp = nodep->lhsp();
+        CONST_BITOP_RETURN_IF(VN_IS(lhsp, And) || VN_IS(lhsp, Or) || VN_IS(lhsp, Const), lhsp);
+        incrOps(nodep, __LINE__);
+        m_polarity = !m_polarity;
+        iterateChildren(nodep);
+        // Don't restore m_polarity for Xor as it counts parity of the entire tree
+        if (!isXorTree()) m_polarity = !m_polarity;
+    }
+    virtual void visit(AstWordSel* nodep) override {
+        CONST_BITOP_RETURN_IF(!m_leafp, nodep);
+        AstConst* constp = VN_CAST(nodep->bitp(), Const);
+        CONST_BITOP_RETURN_IF(!constp, nodep->rhsp());
+        UASSERT_OBJ(m_leafp->m_wordIdx == -1, nodep, "Unexpected nested WordSel");
+        m_leafp->m_wordIdx = constp->toSInt();
+        iterate(nodep->fromp());
+    }
+    virtual void visit(AstVarRef* nodep) override {
+        CONST_BITOP_RETURN_IF(!m_leafp, nodep);
+        UASSERT_OBJ(!m_leafp->m_refp, nodep, m_leafp->m_refp << " is already set");
+        m_leafp->m_refp = nodep;
+        m_leafp->m_polarity = m_polarity;
+        m_leafp->m_lsb = m_lsb;
+    }
+    virtual void visit(AstConst* nodep) override {
+        CONST_BITOP_RETURN_IF(!m_leafp, nodep);
+        UASSERT_OBJ(!m_leafp->m_constp, nodep, m_leafp->m_constp << " is already set");
+        m_leafp->m_constp = nodep;
+        m_leafp->m_lsb = m_lsb;
+    }
+
+    virtual void visit(AstRedXor* nodep) override {  // Expect '^(mask & v)'
+        CONST_BITOP_RETURN_IF(!VN_IS(m_rootp, Xor), nodep);
+        AstAnd* andp = VN_CAST(nodep->lhsp(), And);
+        CONST_BITOP_RETURN_IF(!andp, nodep->lhsp());
+
+        auto mask = findLeaf(andp->lhsp(), true);
+        CONST_BITOP_RETURN_IF(!mask.m_constp || mask.m_lsb != 0, andp->lhsp());
+
+        LeafInfo leaf = findLeaf(andp->rhsp(), false);
+        CONST_BITOP_RETURN_IF(!leaf.m_refp, andp->rhsp());
+
+        incrOps(nodep, __LINE__);
+        incrOps(andp, __LINE__);
+        const V3Number& maskNum = mask.m_constp->num();
+        VarInfo& varInfo = getVarInfo(leaf);
+        for (int i = 0; i < maskNum.width(); ++i) {
+            // Set true, m_treePolarity takes care of the entire parity
+            if (maskNum.bitIs1(i)) varInfo.setPolarity(true, i + leaf.m_lsb);
+        }
+    }
+
+    virtual void visit(AstNodeBiop* nodep) override {
+        auto isConst = [](AstNode* nodep, vluint64_t v) -> bool {
+            AstConst* constp = VN_CAST(nodep, Const);
+            return constp && constp->toUQuad() == v;
+        };
+        if (nodep->type() == m_rootp->type()) {  // And, Or, Xor
+            CONST_BITOP_RETURN_IF(!m_polarity && isXorTree(), nodep);
+            incrOps(nodep, __LINE__);
+            VL_RESTORER(m_curOpp);
+            VL_RESTORER(m_leafp);
+
+            for (int i = 0; i < 2; ++i) {
+                LeafInfo leafInfo;
+                m_leafp = &leafInfo;
+                m_curOpp = i == 0 ? nodep->lhsp() : nodep->rhsp();
+                const size_t origFrozens = m_frozenNodes.size();
+                const int origOps = m_ops;
+                const bool origFailed = m_failed;
+                iterate(m_curOpp);
+                if (leafInfo.m_constp || m_failed) {
+                    // Rvert changes in leaf
+                    if (m_frozenNodes.size() > origFrozens) m_frozenNodes.resize(origFrozens);
+                    m_frozenNodes.push_back(m_curOpp);
+                    m_ops = origOps;
+                    m_failed = origFailed;
+                } else if (leafInfo.m_refp) {
+                    VarInfo& varInfo = getVarInfo(leafInfo);
+                    if (!varInfo.hasConstantResult()) {
+                        varInfo.setPolarity(isXorTree() || leafInfo.m_polarity, leafInfo.m_lsb);
+                    }
+                }
+            }
+            return;
+        } else if (VN_IS(m_rootp, Xor) && VN_IS(nodep, Eq) && isConst(nodep->lhsp(), 0)
+                   && VN_IS(nodep->rhsp(), And)) {  // 0 == (1 & RedXor)
+            AstAnd* andp = static_cast<AstAnd*>(nodep->rhsp());  // already checked above
+            CONST_BITOP_RETURN_IF(!isConst(andp->lhsp(), 1), andp->lhsp());
+            AstRedXor* redXorp = VN_CAST(andp->rhsp(), RedXor);
+            CONST_BITOP_RETURN_IF(!redXorp, andp->rhsp());
+            incrOps(nodep, __LINE__);
+            incrOps(andp, __LINE__);
+            m_polarity = !m_polarity;
+            iterate(redXorp);
+            return;
+        } else if (VN_IS(m_rootp, Xor) && VN_IS(nodep, And) && isConst(nodep->lhsp(), 1)
+                   && (VN_IS(nodep->rhsp(), Xor)
+                       || VN_IS(nodep->rhsp(), RedXor))) {  // 1 & (v[3] ^ v[2])
+            incrOps(nodep, __LINE__);
+            iterate(nodep->rhsp());
+            return;
+        } else if ((isAndTree() && VN_IS(nodep, Eq)) || (isOrTree() && VN_IS(nodep, Neq))) {
+            CONST_BITOP_RETURN_IF(!m_polarity, nodep);
+            const bool maskFlip = isOrTree();
+            LeafInfo comp = findLeaf(nodep->lhsp(), true);
+            CONST_BITOP_RETURN_IF(!comp.m_constp || comp.m_lsb != 0, nodep->lhsp());
+
+            AstAnd* andp = VN_CAST(nodep->rhsp(), And);  // comp == (mask & v)
+            CONST_BITOP_RETURN_IF(!andp, nodep->rhsp());
+
+            LeafInfo mask = findLeaf(andp->lhsp(), true);
+            CONST_BITOP_RETURN_IF(!mask.m_constp || mask.m_lsb != 0, andp->lhsp());
+
+            LeafInfo ref = findLeaf(andp->rhsp(), false);
+            CONST_BITOP_RETURN_IF(!ref.m_refp, andp->rhsp());
+
+            VarInfo& varInfo = getVarInfo(ref);
+
+            const V3Number maskNum = mask.m_constp->num();
+            const V3Number compNum = comp.m_constp->num();
+            for (int i = 0; i < maskNum.width() && !varInfo.hasConstantResult(); ++i) {
+                const int bit = i + ref.m_lsb;
+                if (maskNum.bitIs0(i)) continue;
+                varInfo.setPolarity(compNum.bitIs1(i) ^ maskFlip, bit);
+            }
+            incrOps(nodep, __LINE__);
+            incrOps(andp, __LINE__);
+            return;
+        }
+        CONST_BITOP_SET_FAILED("Mixture of different ops cannot be optimized", nodep);
+    }
+
+    // CONSTRUCTORS
+    ConstBitOpTreeVisitor(AstNode* nodep, int ops)
+        : m_ops(ops)
+        , m_rootp(nodep) {
+        // Fill nullptr at [0] because AstVarScope::user4 is 0 by default
+        m_varInfos.push_back(nullptr);
+        CONST_BITOP_RETURN_IF(!isAndTree() && !isOrTree() && !isXorTree(), nodep);
+        AstNode::user4ClearTree();
+        if (AstNodeBiop* biopp = VN_CAST(nodep, NodeBiop)) {
+            iterate(biopp);
+        } else {
+            incrOps(nodep, __LINE__);
+            iterateChildren(nodep);
+        }
+        UASSERT_OBJ(isXorTree() || m_polarity, nodep, "must be the original polarity");
+    }
+    virtual ~ConstBitOpTreeVisitor() {
+        for (size_t i = 0; i < m_varInfos.size(); ++i) {
+            VL_DO_DANGLING(delete m_varInfos[i], m_varInfos[i]);
+        }
+    }
+#undef CONST_BITOP_RETURN_IF
+#undef CONST_BITOP_SET_FAILED
+
+public:
+    // Transform as below.
+    // v[0] & v[1] => 2'b11 == (2'b11 & v)
+    // v[0] | v[1] => 2'b00 != (2'b11 & v)
+    // v[0] ^ v[1] => ^{2'b11 & v}
+    // (3'b011 == (3'b011 & v)) & v[2]  => 3'b111 == (3'b111 & v)
+    // (3'b000 != (3'b011 & v)) | v[2]  => 3'b000 != (3'b111 & v)
+    // Reduction ops are transformed in the same way.
+    // &{v[0], v[1]} => 2'b11 == (2'b11 & v)
+    static AstNode* simplify(AstNode* nodep, int ops, VDouble0& reduction) {
+        ConstBitOpTreeVisitor visitor{nodep, ops};
+        if (visitor.m_failed || visitor.m_varInfos.size() == 1) return nullptr;
+
+        // Two ops for each varInfo. (And and Eq)
+        const int vars = visitor.m_varInfos.size() - 1;
+        int constTerms = 0;
+        for (const VarInfo* v : visitor.m_varInfos) {
+            if (v && v->hasConstantResult()) ++constTerms;
+        }
+        // Expected number of ops after this simplification
+        // e.g. (comp0 == (mask0 & var0)) & (comp1 == (mask1 & var1)) & ....
+        // e.g. redXor(mask1 & var0) ^ redXor(mask1 & var1)
+        //  2 ops per variables, numVars - 1 ops among variables
+        int expOps = 2 * (vars - constTerms) + vars - 1;
+        expOps += 2 * visitor.m_frozenNodes.size();
+        if (visitor.isXorTree()) {
+            ++expOps;  // AstRedXor::cleanOut() == false, so need 1 & redXor
+            if (!visitor.m_polarity) ++expOps;  // comparison with 0
+        }
+        if (visitor.m_ops <= expOps) return nullptr;  // Unless benefitial, return
+
+        reduction += visitor.m_ops - expOps;
+
+        AstNode* resultp = nullptr;
+        // VarInfo in visitor.m_varInfos appears in deterministic order,
+        // so the optimized AST is deterministic too.
+        for (const VarInfo* varinfop : visitor.m_varInfos) {
+            if (!varinfop) continue;
+            AstNode* partialresultp = varinfop->getResult();
+            resultp = visitor.combineTree(resultp, partialresultp);
+        }
+        AstNode* frozensp = nullptr;
+        for (AstNode* frozenp : visitor.m_frozenNodes) {
+            frozenp->unlinkFrBack();
+            frozensp = visitor.combineTree(frozensp, frozenp);
+        }
+        if (frozensp) resultp = visitor.combineTree(resultp, frozensp);
+
+        if (visitor.isXorTree()) {
+            // VL_REDXOR_N functions don't guarantee to return only 0/1
+            const int width = resultp->width();
+            FileLine* fl = nodep->fileline();
+            resultp = new AstAnd{fl, new AstConst{fl, V3Number{nodep, width, 1}}, resultp};
+            if (!visitor.m_polarity) {
+                resultp = new AstEq{fl, new AstConst{fl, V3Number{nodep, width, 0}}, resultp};
+                resultp->dtypep()->widthForce(1, 1);
+            }
+        }
+        if (resultp->width() != nodep->width()) {
+            resultp = new AstCCast{resultp->fileline(), resultp, nodep};
+        }
+        return resultp;
+    }
+};
+
 //######################################################################
 // Const state, as a visitor of each AstNode

@ -104,6 +519,7 @@ private:
    AstArraySel* m_selp = nullptr;  // Current select
    AstNode* m_scopep = nullptr;  // Current scope
    AstAttrOf* m_attrp = nullptr;  // Current attribute
+    VDouble0 m_statBitOpReduction;  // Ops reduced in ConstBitOpTreeVisitor

    // METHODS
    VL_DEBUG_FUNC;  // Declare debug()
@ -270,6 +686,36 @@ private:
        VL_DO_DANGLING(nodep->deleteTree(), nodep);
        return true;
    }
+    bool matchBitOpTree(AstNode* nodep) {
+        AstNode* newp = nullptr;
+        bool tried = false;
+        if (AstAnd* andp = VN_CAST(nodep, And)) {  // 1 & BitOpTree
+            if (AstConst* bitMaskp = VN_CAST(andp->lhsp(), Const)) {
+                if (bitMaskp->num().toUQuad() != 1) return false;
+                newp = ConstBitOpTreeVisitor::simplify(andp->rhsp(), 1, m_statBitOpReduction);
+                tried = true;
+            }
+        }
+        if (!tried) {
+            // (comp == BitOpTree) & BitOpTree
+            // (comp != BitOpTree) | BitOpTree
+            newp = ConstBitOpTreeVisitor::simplify(nodep, 0, m_statBitOpReduction);
+        }
+        if (newp) {
+            UINFO(4, "Transformed leaf of bit tree to " << newp << std::endl);
+            if (debug() >= 9) {
+                static int c = 0;
+                std::cout << "Call matchBitOpTree[" << c << "]\n";
+                nodep->dumpTree(std::cout);
+                std::cout << "\nResult:\n";
+                newp->dumpTree(std::cout);
+                ++c;
+            }
+            nodep->replaceWith(newp);
+            VL_DO_DANGLING(nodep->deleteTree(), nodep);
+        }
+        return newp;
+    }
    static bool operandShiftSame(const AstNode* nodep) {
        const AstNodeBiop* np = VN_CAST_CONST(nodep, NodeBiop);
        {
@ -2477,6 +2923,7 @@ private:
    TREEOPV("AstRedOr {$lhsp.castExtend}",      "AstRedOr {$lhsp->castExtend()->lhsp()}");
    TREEOPV("AstRedXor{$lhsp.castExtend}",      "AstRedXor{$lhsp->castExtend()->lhsp()}");
    TREEOP ("AstRedXor{$lhsp.castXor, VN_IS(VN_CAST($lhsp,,Xor)->lhsp(),,Const)}", "AstXor{AstRedXor{$lhsp->castXor()->lhsp()}, AstRedXor{$lhsp->castXor()->rhsp()}}");  // ^(const ^ a) => (^const)^(^a)
+    TREEOPC("AstAnd {nodep->widthMin() == 1, $lhsp.castConst, $rhsp.castRedXor, matchBitOpTree(nodep)}", "DONE");
    TREEOPV("AstOneHot{$lhsp.width1}",          "replaceWLhs(nodep)");
    TREEOPV("AstOneHot0{$lhsp.width1}",         "replaceNum(nodep,1)");
    // Binary AND/OR is faster than logical and/or (usually)
@ -2498,6 +2945,9 @@ private:
    TREEOP ("AstAnd {operandShiftSame(nodep)}",         "replaceShiftSame(nodep)");
    TREEOP ("AstOr  {operandShiftSame(nodep)}",         "replaceShiftSame(nodep)");
    TREEOP ("AstXor {operandShiftSame(nodep)}",         "replaceShiftSame(nodep)");
+    TREEOPC("AstAnd {nodep->widthMin() == 1, matchBitOpTree(nodep)}", "DONE");
+    TREEOPC("AstOr  {nodep->widthMin() == 1, matchBitOpTree(nodep)}", "DONE");
+    TREEOPC("AstXor {nodep->widthMin() == 1, matchBitOpTree(nodep)}", "DONE");
    // Note can't simplify a extend{extends}, extends{extend}, as the sign
    // bits end up in the wrong places
    TREEOPV("AstExtend {$lhsp.castExtend}",  "replaceExtend(nodep, VN_CAST(nodep->lhsp(), Extend)->lhsp())");
@ -2595,7 +3045,12 @@ public:
        }
        // clang-format on
    }
-    virtual ~ConstVisitor() override = default;
+    virtual ~ConstVisitor() override {
+        if (m_doCpp) {
+            V3Stats::addStat("Optimizations, Const bit op reduction", m_statBitOpReduction);
+        }
+    }
+
    AstNode* mainAcceptEdit(AstNode* nodep) {
        // Operate starting at a random place
        return iterateSubtreeReturnEdits(nodep);
--- a/test_regress/t/t_const_opt_red.pl
+++ b/test_regress/t/t_const_opt_red.pl
@ -11,12 +11,16 @@ if (!$::Driver) { use FindBin; exec("$FindBin::Bin/bootstrap.pl", @ARGV, $0); di
 scenarios(simulator => 1);

 compile(
-    verilator_flags2=>["-Wno-UNOPTTHREADS"],
+    verilator_flags2=>["-Wno-UNOPTTHREADS", "--stats"],
    );

 execute(
    check_finished => 1,
    );

+if ($Self->{vlt}) {
+    file_grep($Self->{stats}, qr/Optimizations, Const bit op reduction\s+(\d+)/i, 135);
+}
+
 ok(1);
 1;
--- a/test_regress/t/t_func_crc.pl
+++ b/test_regress/t/t_func_crc.pl
@ -11,12 +11,16 @@ if (!$::Driver) { use FindBin; exec("$FindBin::Bin/bootstrap.pl", @ARGV, $0); di
 scenarios(simulator => 1);

 compile(
-    verilator_flags2 => ["--compiler msvc"],  # We have deep expressions we want to test
+    verilator_flags2 => ["--compiler msvc", "--stats"],  # We have deep expressions we want to test
    );

 execute(
    check_finished => 1,
    );

+if ($Self->{vlt}) {
+    file_grep($Self->{stats}, qr/Optimizations, Const bit op reduction\s+(\d+)/i, 3888);
+}
+
 ok(1);
 1;
--- a/test_regress/t/t_gate_ormux.pl
+++ b/test_regress/t/t_gate_ormux.pl
@ -15,9 +15,13 @@ $Self->{sim_time} = $Self->{cycles} * 10 + 1000;

 compile(
    v_flags2 => ["+define+SIM_CYCLES=$Self->{cycles}",],
-    verilator_flags2=>["-Wno-UNOPTTHREADS"],
+    verilator_flags2=>["-Wno-UNOPTTHREADS", "--stats"],
    );

+if ($Self->{vlt}) {
+    file_grep($Self->{stats}, qr/Optimizations, Const bit op reduction\s+(\d+)/i, 994);
+}
+
 execute(
    );

--- a/test_regress/t/t_merge_cond.pl
+++ b/test_regress/t/t_merge_cond.pl
@ -21,9 +21,9 @@ execute(
 if ($Self->{vlt}) {
    # Note, with vltmt this might be split differently, so only checking vlt
    file_grep($Self->{stats}, qr/Optimizations, MergeCond merges\s+(\d+)/i,
-              11);
+              10);
    file_grep($Self->{stats}, qr/Optimizations, MergeCond merged items\s+(\d+)/i,
-              644);
+              580);
    file_grep($Self->{stats}, qr/Optimizations, MergeCond longest merge\s+(\d+)/i,
              64);
 }