Deprecate isolate_assignments attribute

As per discussion. Remove the unsound V3SplitAs pass. The
isolate_assignments attribute/directive is now parsed and ignored in the
frontend for compatibility but otherwise have no effect.

Fixes #7144

docs/guide/control.rst

@@ -187,6 +187,10 @@ The grammar of control commands is as follows:
 
 .. option:: isolate_assignments -module "<modulename>" [-task "<taskname>"] -var "<signame>"
 
+   Deprecated and has no effect (ignored).
+
+   In versions before 5.050:
+
    Used to indicate that the assignments to this signal in any blocks
    should be isolated into new blocks. Same as
    :option:`/*verilator&32;isolate_assignments*/` metacomment.

docs/guide/extensions.rst

@@ -341,6 +341,10 @@ or "`ifdef`"'s may break other tools.
 
 .. option:: /*verilator&32;isolate_assignments*/
 
+   Deprecated and has no effect (ignored).
+
+   In versions before 5.050:
+
    Used after a signal declaration to indicate the assignments to this
    signal in any blocks should be isolated into new blocks. When large
    combinatorial block results in a :option:`UNOPTFLAT` warning, attaching

docs/guide/warnings.rst

@@ -2366,11 +2366,6 @@ List Of Warnings
    the conflict. If you run with :vlopt:`--report-unoptflat`, Verilator will
    suggest possible candidates for :option:`/*verilator&32;split_var*/`.
 
-   The UNOPTFLAT warning may also occur where outputs from a block of logic
-   are independent, but occur in the same always block. To fix this, use
-   the :option:`/*verilator&32;isolate_assignments*/` metacomment described
-   above.
-
    Before version 5.000, the UNOPTFLAT warning may also have been due to
    clock enables, identified from the reported path going through a clock
    gating instance. To fix these, the clock_enable meta comment was used.

src/CMakeLists.txt

@@ -175,7 +175,6 @@ set(HEADERS
     V3Simulate.h
     V3Slice.h
     V3Split.h
-    V3SplitAs.h
     V3SplitVar.h
     V3StackCount.h
     V3Stats.h
@@ -350,7 +349,6 @@ set(COMMON_SOURCES
     V3Scoreboard.cpp
     V3Slice.cpp
     V3Split.cpp
-    V3SplitAs.cpp
     V3SplitVar.cpp
     V3StackCount.cpp
     V3Stats.cpp

src/Makefile_obj.in

@@ -333,7 +333,6 @@ RAW_OBJS_PCH_ASTNOMT = \
   V3Scoreboard.o \
   V3Slice.o \
   V3Split.o \
-  V3SplitAs.o \
   V3SplitVar.o \
   V3StackCount.o \
   V3Subst.o \

src/V3AstAttr.h

@@ -342,7 +342,6 @@ public:
         VAR_PUBLIC_FLAT,                // V3LinkParse moves to AstVar::sigPublic
         VAR_PUBLIC_FLAT_RD,             // V3LinkParse moves to AstVar::sigPublic
         VAR_PUBLIC_FLAT_RW,             // V3LinkParse moves to AstVar::sigPublic
-        VAR_ISOLATE_ASSIGNMENTS,        // V3LinkParse moves to AstVar::attrIsolateAssign
         VAR_SC_BIGUINT,                 // V3LinkParse moves to AstVar::attrScBigUint
         VAR_SC_BV,                      // V3LinkParse moves to AstVar::attrScBv
         VAR_SFORMAT,                    // V3LinkParse moves to AstVar::attrSFormat
@@ -364,7 +363,7 @@ public:
             "TYPEID", "TYPENAME",
             "VAR_BASE", "VAR_FORCEABLE", "VAR_FSM_ARC_INCLUDE_COND", "VAR_FSM_RESET_ARC",
             "VAR_FSM_STATE", "VAR_PORT_DTYPE", "VAR_PUBLIC", "VAR_PUBLIC_FLAT",
-            "VAR_PUBLIC_FLAT_RD", "VAR_PUBLIC_FLAT_RW", "VAR_ISOLATE_ASSIGNMENTS",
+            "VAR_PUBLIC_FLAT_RD", "VAR_PUBLIC_FLAT_RW",
             "VAR_SC_BIGUINT", "VAR_SC_BV", "VAR_SFORMAT", "VAR_SPLIT_VAR"
         };
         // clang-format on

src/V3AstNodeOther.h

@@ -97,7 +97,6 @@ class AstNodeFTask VL_NOT_FINAL : public AstNode {
     string m_ifacePortName;  // Interface port name for out-of-block definition (IEEE 25.8)
     uint64_t m_dpiOpenParent = 0;  // DPI import open array, if !=0, how many callees
     bool m_taskPublic : 1;  // Public task
-    bool m_attrIsolateAssign : 1;  // User isolate_assignments attribute
     bool m_classMethod : 1;  // Class method
     bool m_didProto : 1;  // Did prototype processing
     bool m_prototype : 1;  // Just a prototype
@@ -130,7 +129,6 @@ protected:
         : AstNode{t, fl}
         , m_name{name}
         , m_taskPublic{false}
-        , m_attrIsolateAssign{false}
         , m_classMethod{false}
         , m_didProto{false}
         , m_prototype{false}
@@ -179,8 +177,6 @@ public:
     uint64_t dpiOpenParent() const { return m_dpiOpenParent; }
     bool taskPublic() const { return m_taskPublic; }
     void taskPublic(bool flag) { m_taskPublic = flag; }
-    bool attrIsolateAssign() const { return m_attrIsolateAssign; }
-    void attrIsolateAssign(bool flag) { m_attrIsolateAssign = flag; }
     bool classMethod() const { return m_classMethod; }
     void classMethod(bool flag) { m_classMethod = flag; }
     bool didProto() const { return m_didProto; }
@@ -2134,7 +2130,6 @@ class AstVar final : public AstNode {
     bool m_funcReturn : 1;  // Return variable for a function
     bool m_attrScBv : 1;  // User force bit vector attribute
     bool m_attrScBigUint : 1;  // User force sc_biguint attribute
-    bool m_attrIsolateAssign : 1;  // User isolate_assignments attribute
     bool m_attrSFormat : 1;  // User sformat attribute
     bool m_attrSplitVar : 1;  // declared with split_var metacomment
     bool m_attrFsmState : 1;  // declared with fsm_state metacomment
@@ -2197,7 +2192,6 @@ class AstVar final : public AstNode {
         m_funcReturn = false;
         m_attrScBv = false;
         m_attrScBigUint = false;
-        m_attrIsolateAssign = false;
         m_attrSFormat = false;
         m_attrSplitVar = false;
         m_attrFsmState = false;
@@ -2346,7 +2340,6 @@ public:
     void attrFileDescr(bool flag) { m_fileDescr = flag; }
     void attrScBv(bool flag) { m_attrScBv = flag; }
     void attrScBigUint(bool flag) { m_attrScBigUint = flag; }
-    void attrIsolateAssign(bool flag) { m_attrIsolateAssign = flag; }
     void attrSFormat(bool flag) { m_attrSFormat = flag; }
     void attrSplitVar(bool flag) { m_attrSplitVar = flag; }
     void attrFsmState(bool flag) { m_attrFsmState = flag; }
@@ -2522,7 +2515,6 @@ public:
     bool attrFsmRegisterWrapper() const { return m_attrFsmRegisterWrapper; }
     bool attrFsmResetArc() const { return m_attrFsmResetArc; }
     bool attrFsmArcInclCond() const { return m_attrFsmArcInclCond; }
-    bool attrIsolateAssign() const { return m_attrIsolateAssign; }
     AstIface* sensIfacep() const { return m_sensIfacep; }
     VRandAttr rand() const { return m_rand; }
     string verilogKwd() const override;
@@ -2534,7 +2526,6 @@ public:
         // This is getting connected to fromp; keep attributes
         // Note the method below too
         if (fromp->attrFileDescr()) attrFileDescr(true);
-        if (fromp->attrIsolateAssign()) attrIsolateAssign(true);
         if (fromp->isContinuously()) isContinuously(true);
     }
     void propagateWrapAttrFrom(const AstVar* fromp) {

src/V3AstNodes.cpp

@@ -3205,7 +3205,6 @@ void AstVar::dump(std::ostream& str) const {
     if (noReset()) str << " [!RST]";
     if (processQueue()) str << " [PROCQ]";
     if (sampled()) str << " [SAMPLED]";
-    if (attrIsolateAssign()) str << " [aISO]";
     if (attrFsmState()) str << " [aFSMSTATE]";
     if (attrFsmResetArc()) str << " [aFSMRESETARC]";
     if (attrFsmArcInclCond()) str << " [aFSMARCCOND]";
@@ -3240,7 +3239,6 @@ void AstVar::dumpJson(std::ostream& str) const {
     dumpJsonBoolFuncIf(str, noReset);
     dumpJsonBoolFuncIf(str, processQueue);
     dumpJsonBoolFuncIf(str, sampled);
-    dumpJsonBoolFuncIf(str, attrIsolateAssign);
     dumpJsonBoolFuncIf(str, attrFsmState);
     dumpJsonBoolFuncIf(str, attrFsmResetArc);
     dumpJsonBoolFuncIf(str, attrFsmArcInclCond);

src/V3Control.cpp

@@ -182,7 +182,6 @@ class V3ControlFTask final {
     V3ControlVarResolver m_params;  // Parameters in function/task
     V3ControlVarResolver m_ports;  // Ports in function/task
     V3ControlVarResolver m_vars;  // Variables in function/task
-    bool m_isolate = false;  // Isolate function return
     bool m_noinline = false;  // Don't inline function/task
     bool m_public = false;  // Public function/task
 
@@ -190,7 +189,6 @@ public:
     V3ControlFTask() = default;
     void update(const V3ControlFTask& f) {
         // Don't overwrite true with false
-        if (f.m_isolate) m_isolate = true;
         if (f.m_noinline) m_noinline = true;
         if (f.m_public) m_public = true;
         m_params.update(f.m_params);
@@ -203,7 +201,6 @@ public:
     V3ControlVarResolver& ports() { return m_ports; }
     V3ControlVarResolver& vars() { return m_vars; }
 
-    void setIsolate(bool set) { m_isolate = set; }
     void setNoInline(bool set) { m_noinline = set; }
     void setPublic(bool set) { m_public = set; }
 
@@ -212,8 +209,6 @@ public:
             ftaskp->addStmtsp(new AstPragma{ftaskp->fileline(), VPragmaType::NO_INLINE_TASK});
         if (m_public)
             ftaskp->addStmtsp(new AstPragma{ftaskp->fileline(), VPragmaType::PUBLIC_TASK});
-        // Only functions can have isolate (return value)
-        if (VN_IS(ftaskp, Func)) ftaskp->attrIsolateAssign(m_isolate);
     }
 };
 
@@ -981,13 +976,7 @@ void V3Control::addVarAttr(FileLine* fl, const string& module, const string& fta
 
     // Semantics: Most of the attributes operate on signals
     if (pattern.empty()) {
-        if (attr == VAttrType::VAR_ISOLATE_ASSIGNMENTS) {
+        if (attr == VAttrType::VAR_PUBLIC) {
-            if (ftask.empty()) {
-                fl->v3error("isolate_assignments only applies to signals or functions/tasks");
-            } else {
-                V3ControlResolver::s().modules().at(module).ftasks().at(ftask).setIsolate(true);
-            }
-        } else if (attr == VAttrType::VAR_PUBLIC) {
             if (ftask.empty()) {
                 // public module, this is the only exception from var here
                 V3ControlResolver::s().modules().at(module).addModulePragma(

src/V3LinkDot.cpp

@@ -1727,7 +1727,6 @@ class LinkDotFindVisitor final : public VNVisitor {
             newvarp->lifetime(VLifetime::AUTOMATIC_EXPLICIT);
             newvarp->funcReturn(true);
             newvarp->trace(false);  // Not user visible
-            newvarp->attrIsolateAssign(nodep->attrIsolateAssign());
             nodep->fvarp(newvarp);
             // Explicit insert required, as the var name shadows the upper level's task name
             m_statep->insertSym(m_curSymp, newvarp->name(), newvarp, nullptr /*classOrPackagep*/);

src/V3LinkParse.cpp

@@ -606,10 +606,6 @@ class LinkParseVisitor final : public VNVisitor {
             UASSERT_OBJ(m_varp, nodep, "Attribute not attached to variable");
             m_varp->sigUserRWPublic(true);
             VL_DO_DANGLING(nodep->unlinkFrBack()->deleteTree(), nodep);
-        } else if (nodep->attrType() == VAttrType::VAR_ISOLATE_ASSIGNMENTS) {
-            UASSERT_OBJ(m_varp, nodep, "Attribute not attached to variable");
-            m_varp->attrIsolateAssign(true);
-            VL_DO_DANGLING(nodep->unlinkFrBack()->deleteTree(), nodep);
         } else if (nodep->attrType() == VAttrType::VAR_SFORMAT) {
             UASSERT_OBJ(m_varp, nodep, "Attribute not attached to variable");
             m_varp->attrSFormat(true);

src/V3SchedAcyclic.cpp

@@ -351,8 +351,7 @@ std::string reportLoopVars(FileLine* /*warnFl*/, Graph* graphp, SchedAcyclicVarV
 
     if (splittable) {
         ss << V3Error::warnMore()
-           << "... Suggest add /*verilator split_var*/ or /*verilator "
+           << "... Suggest add /*verilator split_var*/ to appropriate variables above.\n";
-              "isolate_assignments*/ to appropriate variables above.\n";
     }
     V3Stats::addStat("Scheduling, split_var, candidates", splittable);
     return ss.str();

src/V3SplitAs.cpp

@@ -1,195 +0,0 @@
-// -*- mode: C++; c-file-style: "cc-mode" -*-
-//*************************************************************************
-// DESCRIPTION: Verilator: Break always into separate statements to reduce temps
-//
-// Code available from: https://verilator.org
-//
-//*************************************************************************
-//
-// 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-FileCopyrightText: 2003-2026 Wilson Snyder
-// SPDX-License-Identifier: LGPL-3.0-only OR Artistic-2.0
-//
-//*************************************************************************
-// V3SplitAs's Transformations:
-//
-//      Search each ALWAYS for a VARREF lvalue with a /*isolate_assignments*/ attribute
-//      If found, color statements with both, assignment to that varref, or other assignments.
-//      Replicate the Always, and remove mis-colored duplicate code.
-//
-//*************************************************************************
-
-#include "V3PchAstNoMT.h"  // VL_MT_DISABLED_CODE_UNIT
-
-#include "V3SplitAs.h"
-
-#include "V3Stats.h"
-
-VL_DEFINE_DEBUG_FUNCTIONS;
-
-//######################################################################
-// Find all split variables in a block
-
-class SplitAsFindVisitor final : public VNVisitorConst {
-    // STATE - across all visitors
-    AstVarScope* m_splitVscp = nullptr;  // Variable we want to split
-
-    // METHODS
-    void visit(AstVarRef* nodep) override {
-        if (nodep->access().isWriteOrRW() && !m_splitVscp && nodep->varp()->attrIsolateAssign()) {
-            m_splitVscp = nodep->varScopep();
-        }
-    }
-    void visit(AstExprStmt* nodep) override {
-        // A function call inside the splitting assignment
-        // We need to presume the whole call is preserved (if the upper statement is)
-        // This will break if the m_splitVscp is a "ref" argument to the function,
-        // but little we can do.
-    }
-    void visit(AstNode* nodep) override { iterateChildrenConst(nodep); }
-
-public:
-    // CONSTRUCTORS
-    explicit SplitAsFindVisitor(AstAlways* nodep) { iterateConst(nodep); }
-    ~SplitAsFindVisitor() override = default;
-    // METHODS
-    AstVarScope* splitVscp() const { return m_splitVscp; }
-};
-
-//######################################################################
-// Remove nodes not containing proper references
-
-class SplitAsCleanVisitor final : public VNVisitor {
-    // STATE - across all visitors
-    const AstVarScope* const m_splitVscp;  // Variable we want to split
-    const bool m_modeMatch;  // Remove matching Vscp, else non-matching
-    // STATE - for current visit position (use VL_RESTORER)
-    bool m_keepStmt = false;  // Current Statement must be preserved
-    bool m_matches = false;  // Statement below has matching lvalue reference
-
-    // METHODS
-    void visit(AstVarRef* nodep) override {
-        if (nodep->access().isWriteOrRW()) {
-            if (nodep->varScopep() == m_splitVscp) {
-                UINFO(6, "       CL VAR " << nodep);
-                m_matches = true;
-            }
-        }
-    }
-    void visit(AstNodeStmt* nodep) override {
-        UINFO(6, "     CL STMT " << nodep);
-        const bool oldKeep = m_keepStmt;
-        {
-            VL_RESTORER(m_matches);
-            m_matches = false;
-            m_keepStmt = false;
-
-            iterateChildren(nodep);
-
-            if (m_keepStmt || (m_modeMatch ? m_matches : !m_matches)) {
-                UINFO(6, "     Keep   STMT " << nodep);
-                m_keepStmt = true;
-            } else {
-                UINFO(6, "     Delete STMT " << nodep);
-                VL_DO_DANGLING(pushDeletep(nodep->unlinkFrBack()), nodep);
-            }
-        }
-        // If something below matches, the upper statement remains too.
-        m_keepStmt = oldKeep || m_keepStmt;
-        UINFO(9, "     upKeep=" << m_keepStmt << " STMT " << nodep);
-    }
-    void visit(AstExprStmt* nodep) override {
-        // A function call inside the splitting assignment
-        // We need to presume the whole call is preserved (if the upper statement is)
-        // This will break if the m_splitVscp is a "ref" argument to the function,
-        // but little we can do.
-    }
-    void visit(AstNode* nodep) override { iterateChildren(nodep); }
-
-public:
-    // CONSTRUCTORS
-    SplitAsCleanVisitor(AstAlways* nodep, AstVarScope* vscp, bool modeMatch)
-        : m_splitVscp{vscp}
-        , m_modeMatch{modeMatch} {
-        iterate(nodep);
-    }
-    ~SplitAsCleanVisitor() override = default;
-};
-
-//######################################################################
-// SplitAs class functions
-
-class SplitAsVisitor final : public VNVisitor {
-    // NODE STATE
-    //  AstAlways::user()       -> bool.  True if already processed
-    const VNUser1InUse m_inuser1;
-
-    // STATE - across all visitors
-    VDouble0 m_statSplits;  // Statistic tracking
-
-    // METHODS
-    void splitAlways(AstAlways* nodep, AstVarScope* splitVscp) {
-        UINFOTREE(9, nodep, "", "in");
-        // Duplicate it and link in
-        // Below cloneTree should perhaps be cloneTreePure, but given
-        // isolate_assignments is required to hit this code, we presume the user
-        // knows what they are asking for
-        AstAlways* const newp = nodep->cloneTree(false);
-        newp->user1(true);  // So we don't clone it again
-        nodep->addNextHere(newp);
-        {  // Delete stuff we don't want in old
-            const SplitAsCleanVisitor visitor{nodep, splitVscp, false};
-            UINFOTREE(9, nodep, "", "out0");
-        }
-        {  // Delete stuff we don't want in new
-            const SplitAsCleanVisitor visitor{newp, splitVscp, true};
-            UINFOTREE(9, newp, "", "out1");
-        }
-    }
-
-    void visit(AstAlways* nodep) override {
-        // Are there any lvalue references below this?
-        // There could be more than one.  So, we process the first one found first.
-        const AstVarScope* lastSplitVscp = nullptr;
-        while (!nodep->user1()) {
-            // Find any splittable variables
-            const SplitAsFindVisitor visitor{nodep};
-            AstVarScope* const splitVscp = visitor.splitVscp();
-            // Now isolate the always
-            if (splitVscp) {
-                UINFO(3, "Split  " << nodep);
-                UINFO(3, "   For " << splitVscp);
-                // If we did this last time!  Something's stuck!
-                UASSERT_OBJ(splitVscp != lastSplitVscp, nodep,
-                            "Infinite loop in isolate_assignments removal for: "
-                                << splitVscp->prettyNameQ());
-                lastSplitVscp = splitVscp;
-                splitAlways(nodep, splitVscp);
-                ++m_statSplits;
-            } else {
-                nodep->user1(true);
-            }
-        }
-    }
-
-    void visit(AstNodeExpr*) override {}  // Accelerate
-    void visit(AstNode* nodep) override { iterateChildren(nodep); }
-
-public:
-    // CONSTRUCTORS
-    explicit SplitAsVisitor(AstNetlist* nodep) { iterate(nodep); }
-    ~SplitAsVisitor() override {
-        V3Stats::addStat("Optimizations, isolate_assignments blocks", m_statSplits);
-    }
-};
-
-//######################################################################
-// SplitAs class functions
-
-void V3SplitAs::splitAsAll(AstNetlist* nodep) {
-    UINFO(2, __FUNCTION__ << ":");
-    { SplitAsVisitor{nodep}; }  // Destruct before checking
-    V3Global::dumpCheckGlobalTree("splitas", 0, dumpTreeEitherLevel() >= 3);
-}

src/V3SplitAs.h

@@ -1,32 +0,0 @@
-// -*- mode: C++; c-file-style: "cc-mode" -*-
-//*************************************************************************
-// DESCRIPTION: Verilator: Break always into separate statements to reduce temps
-//
-// Code available from: https://verilator.org
-//
-//*************************************************************************
-//
-// 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-FileCopyrightText: 2003-2026 Wilson Snyder
-// SPDX-License-Identifier: LGPL-3.0-only OR Artistic-2.0
-//
-//*************************************************************************
-
-#ifndef VERILATOR_V3SPLITAS_H_
-#define VERILATOR_V3SPLITAS_H_
-
-#include "config_build.h"
-#include "verilatedos.h"
-
-class AstNetlist;
-
-//============================================================================
-
-class V3SplitAs final {
-public:
-    static void splitAsAll(AstNetlist* nodep) VL_MT_DISABLED;
-};
-
-#endif  // Guard

src/Verilator.cpp

@@ -98,7 +98,6 @@
 #include "V3Scoreboard.h"
 #include "V3Slice.h"
 #include "V3Split.h"
-#include "V3SplitAs.h"
 #include "V3SplitVar.h"
 #include "V3Stats.h"
 #include "V3String.h"
@@ -421,7 +420,6 @@ static void process() {
 
             // Split single ALWAYS blocks into multiple blocks for better ordering chances
             if (v3Global.opt.fSplit()) V3Split::splitAll(v3Global.rootp());
-            V3SplitAs::splitAsAll(v3Global.rootp());
 
             // Create tracing sample points, before we start eliminating signals
             if (v3Global.opt.trace()) V3TraceDecl::traceDeclAll(v3Global.rootp());

src/verilog.y

@@ -3121,7 +3121,7 @@ sigAttr<nodep>:
         |       yVL_PUBLIC_FLAT                         { $$ = new AstAttrOf{$1, VAttrType::VAR_PUBLIC_FLAT}; v3Global.dpi(true); }
         |       yVL_PUBLIC_FLAT_RD                      { $$ = new AstAttrOf{$1, VAttrType::VAR_PUBLIC_FLAT_RD}; v3Global.dpi(true); }
         |       yVL_PUBLIC_FLAT_RW attr_event_controlE  { $$ = new AstAttrOf{$1, VAttrType::VAR_PUBLIC_FLAT_RW}; v3Global.dpi(true); DEL($2); }
-        |       yVL_ISOLATE_ASSIGNMENTS                 { $$ = new AstAttrOf{$1, VAttrType::VAR_ISOLATE_ASSIGNMENTS}; }
+        |       yVL_ISOLATE_ASSIGNMENTS                 { $$ = nullptr; /* Historical, now has no effect */ }
         |       yVL_SC_BIGUINT                          { $$ = new AstAttrOf{$1, VAttrType::VAR_SC_BIGUINT}; }
         |       yVL_SC_BV                               { $$ = new AstAttrOf{$1, VAttrType::VAR_SC_BV}; }
         |       yVL_SFORMAT                             { $$ = new AstAttrOf{$1, VAttrType::VAR_SFORMAT}; }
@@ -4657,12 +4657,12 @@ task_prototype<nodeFTaskp>:             // ==IEEE: task_prototype
 
 function_declaration<nodeFTaskp>:       // IEEE: function_declaration + function_body_declaration
                 yFUNCTION dynamic_override_specifiersE lifetimeE funcId funcIsolateE tfGuts yENDFUNCTION endLabelE
-                        { $$ = $4; $4->attrIsolateAssign($5); $$->addStmtsp($6);
+                        { $$ = $4; $$->addStmtsp($6);
                           $$->baseOverride($2);
                           $$->lifetime($3);
                           GRAMMARP->endLabel($<fl>8, $$, $8); }
         |       yFUNCTION dynamic_override_specifiersE lifetimeE funcIdNew funcIsolateE tfNewGuts yENDFUNCTION endLabelE
-                        { $$ = $4; $4->attrIsolateAssign($5); $$->addStmtsp($6);
+                        { $$ = $4; $$->addStmtsp($6);
                           $$->baseOverride($2);
                           $$->lifetime($3);
                           GRAMMARP->endLabel($<fl>8, $$, $8); }
@@ -8553,8 +8553,7 @@ vltVarAttrSpecE<strp>:
         ;
 
 vltVarAttrFront<attrtypeen>:
-                yVLT_ISOLATE_ASSIGNMENTS    { $$ = VAttrType::VAR_ISOLATE_ASSIGNMENTS; }
+                yVLT_FORCEABLE              { $$ = VAttrType::VAR_FORCEABLE; }
-        |       yVLT_FORCEABLE              { $$ = VAttrType::VAR_FORCEABLE; }
         |       yVLT_PUBLIC                 { $$ = VAttrType::VAR_PUBLIC; v3Global.dpi(true); }
         |       yVLT_PUBLIC_FLAT            { $$ = VAttrType::VAR_PUBLIC_FLAT; v3Global.dpi(true); }
         |       yVLT_PUBLIC_FLAT_RD         { $$ = VAttrType::VAR_PUBLIC_FLAT_RD; v3Global.dpi(true); }
@@ -8568,6 +8567,7 @@ vltVarAttrFront<attrtypeen>:
 vltVarAttrFrontDeprecated:
                 yVLT_CLOCK_ENABLE           { }
         |       yVLT_CLOCKER                { }
+        |       yVLT_ISOLATE_ASSIGNMENTS    { }
         |       yVLT_NO_CLOCKER             { }
         ;
 

test_regress/t/t_unopt_combo_isolate.py

@@ -9,37 +9,14 @@
 
 import vltest_bootstrap
 
-test.scenarios('simulator')
+# Note: This test is historical for the isolate_assignments attribute, which
+# was deprecated and has no effect today. This test ensures it still parses
+# in SystemVerilog and Verilator control files for backward compatibility.
+
+test.scenarios('vlt')
 test.top_filename = "t/t_unopt_combo.v"
 
-out_filename = test.obj_dir + "/V" + test.name + ".tree.json"
+test.compile(verilator_flags2=["+define+ISOLATE"])
-
-test.compile(verilator_flags2=[
-    "--no-json-edit-nums", "+define+ISOLATE", "--stats", "-fno-dfg", "-fno-lift-expr"
-])
-
-if test.vlt_all:
-    test.file_grep(test.stats, r'Optimizations, isolate_assignments blocks\s+4')
-    test.file_grep(
-        out_filename,
-        r'{"type":"VAR","name":"t.b",.*"loc":"\w,23:[^"]*",.*"origName":"b",.*"attrIsolateAssign":true,.*"dtypeName":"logic"'
-    )
-    test.file_grep(
-        out_filename,
-        r'{"type":"VAR","name":"__Vfunc_t.file.get_31_16__0__Vfuncout",.*"loc":"\w,99:[^"]*",.*"origName":"__Vfunc_t__DOT__file__DOT__get_31_16__0__Vfuncout",.*"attrIsolateAssign":true,.*"dtypeName":"logic"'
-    )
-    test.file_grep(
-        out_filename,
-        r'{"type":"VAR","name":"__Vfunc_t.file.get_31_16__0__t_crc",.*"loc":"\w,100:[^"]*",.*"origName":"__Vfunc_t__DOT__file__DOT__get_31_16__0__t_crc",.*"attrIsolateAssign":true,.*"dtypeName":"logic"'
-    )
-    test.file_grep(
-        out_filename,
-        r'{"type":"VAR","name":"__Vtask_t.file.set_b_d__1__t_crc",.*"loc":"\w,112:[^"]*",.*"origName":"__Vtask_t__DOT__file__DOT__set_b_d__1__t_crc",.*"attrIsolateAssign":true,.*"dtypeName":"logic"'
-    )
-    test.file_grep(
-        out_filename,
-        r'{"type":"VAR","name":"__Vtask_t.file.set_b_d__1__t_c",.*"loc":"\w,113:[^"]*",.*"origName":"__Vtask_t__DOT__file__DOT__set_b_d__1__t_c",.*"attrIsolateAssign":true,.*"dtypeName":"logic"'
-    )
 
 test.execute()
 

test_regress/t/t_unopt_combo_isolate_vlt.py

@@ -9,38 +9,14 @@
 
 import vltest_bootstrap
 
-test.scenarios('simulator')
+# Note: This test is historical for the isolate_assignments attribute, which
+# was deprecated and has no effect today. This test ensures it still parses
+# in SystemVerilog and Verilator control files for backward compatibility.
+
+test.scenarios('vlt')
 test.top_filename = "t/t_unopt_combo.v"
 
-out_filename = test.obj_dir + "/V" + test.name + ".tree.json"
+test.compile(verilator_flags2=[test.t_dir + "/t_unopt_combo_isolate.vlt"])
-
-test.compile(verilator_flags2=[
-    "--no-json-edit-nums", "--stats", test.t_dir +
-    "/t_unopt_combo_isolate.vlt", "-fno-dfg", "-fno-lift-expr"
-])
-
-if test.vlt_all:
-    test.file_grep(test.stats, r'Optimizations, isolate_assignments blocks\s+4')
-    test.file_grep(
-        out_filename,
-        r'{"type":"VAR","name":"t.b",.*"loc":"\w,23:[^"]*",.*"origName":"b",.*"attrIsolateAssign":true,.*"dtypeName":"logic"'
-    )
-    test.file_grep(
-        out_filename,
-        r'{"type":"VAR","name":"__Vfunc_t.file.get_31_16__0__Vfuncout",.*"loc":"\w,104:[^"]*",.*"origName":"__Vfunc_t__DOT__file__DOT__get_31_16__0__Vfuncout",.*"attrIsolateAssign":true,.*"dtypeName":"logic"'
-    )
-    test.file_grep(
-        out_filename,
-        r'{"type":"VAR","name":"__Vfunc_t.file.get_31_16__0__t_crc",.*"loc":"\w,105:[^"]*",.*"origName":"__Vfunc_t__DOT__file__DOT__get_31_16__0__t_crc",.*"attrIsolateAssign":true,.*"dtypeName":"logic"'
-    )
-    test.file_grep(
-        out_filename,
-        r'{"type":"VAR","name":"__Vtask_t.file.set_b_d__1__t_crc",.*"loc":"\w,115:[^"]*",.*"origName":"__Vtask_t__DOT__file__DOT__set_b_d__1__t_crc",.*"attrIsolateAssign":true,.*"dtypeName":"logic"'
-    )
-    test.file_grep(
-        out_filename,
-        r'{"type":"VAR","name":"__Vtask_t.file.set_b_d__1__t_c",.*"loc":"\w,116:[^"]*",.*"origName":"__Vtask_t__DOT__file__DOT__set_b_d__1__t_c",.*"attrIsolateAssign":true,.*"dtypeName":"logic"'
-    )
 
 test.execute()
 

test_regress/t/t_unoptflat_simple_2_bad.out

@@ -10,5 +10,5 @@
                         t/t_unoptflat_simple_2.v:16:14:  t.x, width 3, circular fanout 2, can split_var
                     ... Candidates with the highest fanout:
                         t/t_unoptflat_simple_2.v:16:14:  t.x, width 3, circular fanout 2, can split_var
-                    ... Suggest add /*verilator split_var*/ or /*verilator isolate_assignments*/ to appropriate variables above.
+                    ... Suggest add /*verilator split_var*/ to appropriate variables above.
 %Error: Exiting due to

test_regress/t/t_vlt_syntax_bad.out

@@ -2,28 +2,25 @@
     9 | public -module "t" @(posedge clk)
       |                    ^
         ... See the manual at https://verilator.org/verilator_doc.html?v=latest for more assistance.
-%Error: t/t_vlt_syntax_bad.vlt:11:1: isolate_assignments only applies to signals or functions/tasks
+%Error: t/t_vlt_syntax_bad.vlt:11:1: Argument -match only supported for lint_off
-   11 | isolate_assignments -module "t"
+   11 | tracing_off --file "*" -match "nothing"
-      | ^~~~~~~~~~~~~~~~~~~
-%Error: t/t_vlt_syntax_bad.vlt:13:1: Argument -match only supported for lint_off
-   13 | tracing_off --file "*" -match "nothing"
       | ^~~~~~~~~~~
+%Error: t/t_vlt_syntax_bad.vlt:13:1: Argument -scope only supported for tracing_on/off
+   13 | lint_off --rule UNOPTFLAT -scope "top*"
+      | ^~~~~~~~
+%Error: t/t_vlt_syntax_bad.vlt:14:1: Argument -scope only supported for tracing_on/off_off
+   14 | lint_off --rule UNOPTFLAT -scope "top*" -levels 0
+      | ^~~~~~~~
 %Error: t/t_vlt_syntax_bad.vlt:15:1: Argument -scope only supported for tracing_on/off
-   15 | lint_off --rule UNOPTFLAT -scope "top*"
+   15 | lint_on --rule UNOPTFLAT -scope "top*"
-      | ^~~~~~~~
+      | ^~~~~~~
 %Error: t/t_vlt_syntax_bad.vlt:16:1: Argument -scope only supported for tracing_on/off_off
-   16 | lint_off --rule UNOPTFLAT -scope "top*" -levels 0
+   16 | lint_on --rule UNOPTFLAT -scope "top*" -levels 0
-      | ^~~~~~~~
-%Error: t/t_vlt_syntax_bad.vlt:17:1: Argument -scope only supported for tracing_on/off
-   17 | lint_on --rule UNOPTFLAT -scope "top*"
       | ^~~~~~~
-%Error: t/t_vlt_syntax_bad.vlt:18:1: Argument -scope only supported for tracing_on/off_off
+%Error: t/t_vlt_syntax_bad.vlt:18:1: forceable missing -module
-   18 | lint_on --rule UNOPTFLAT -scope "top*" -levels 0
+   18 | forceable -module "" -var "net_*"
-      | ^~~~~~~
-%Error: t/t_vlt_syntax_bad.vlt:20:1: forceable missing -module
-   20 | forceable -module "" -var "net_*"
       | ^~~~~~~~~
-%Error: t/t_vlt_syntax_bad.vlt:22:1: missing -var
+%Error: t/t_vlt_syntax_bad.vlt:20:1: missing -var
-   22 | forceable -module "top" -var ""
+   20 | forceable -module "top" -var ""
       | ^~~~~~~~~
 %Error: Exiting due to

test_regress/t/t_vlt_syntax_bad.vlt

@@ -7,8 +7,6 @@
 `verilator_config
 
 public -module "t" @(posedge clk)
-// only signals/functions/tasks
-isolate_assignments -module "t"
 // -match not supported
 tracing_off --file "*" -match "nothing"
 // -scope not supported