Use VIsCached for checking purity of arguments in AstCMethodHard (#8350)

src/V3AstNodeExpr.h

@@ -750,7 +750,7 @@ class AstCMethodHard final : public AstNodeExpr {
     // @astgen op2 := pinsp : List[AstNodeExpr] // Arguments
     // @astgen op3 := withp : Optional[AstWith] // With clause
     VCMethod m_method;  // Which method to call
-    bool m_pure = false;  // Pure optimizable
+    VIsCached m_purity;  // Pure optimizable
     bool m_usePtr = false;  // Use '->' not '.'
 public:
     AstCMethodHard(FileLine* fl, AstNodeExpr* fromp, VCMethod method, AstNodeExpr* pinsp = nullptr)
@@ -758,7 +758,6 @@ public:
         , m_method{method} {
         this->fromp(fromp);
         addPinsp(pinsp);
-        setPurity();
     }
     ASTGEN_MEMBERS_AstCMethodHard;
     void dump(std::ostream& str) const override;
@@ -768,7 +767,10 @@ public:
         const AstCMethodHard* const asamep = VN_DBG_AS(samep, CMethodHard);
         return (m_method == asamep->m_method);
     }
-    bool isPure() override { return m_pure; }
+    bool isPure() override {
+        if (!m_purity.isCached()) m_purity.set(getPurity());
+        return m_purity.get();
+    }
     int instrCount() const override;
     string emitVerilog() override { V3ERROR_NA_RETURN(""); }
     string emitC() override { V3ERROR_NA_RETURN(""); }
@@ -779,7 +781,7 @@ public:
     void method(VCMethod value) { m_method = value; }
 
 private:
-    void setPurity();
+    bool getPurity();
 };
 class AstCReset final : public AstNodeExpr {
     // Reset variable at startup

src/V3AstNodes.cpp

@@ -588,39 +588,34 @@ void AstCFunc::dumpJson(std::ostream& str) const {
 }
 void AstCMethodHard::dump(std::ostream& str) const {
     Super::dump(str);
-    if (m_pure) str << " [PURE]";
+    if (m_purity.get()) str << " [PURE]";
     if (usePtr()) str << " [USEPTR]";
 }
 void AstCMethodHard::dumpJson(std::ostream& str) const {
-    dumpJsonBoolIf(str, "pure", m_pure);
+    dumpJsonBoolIf(str, "pure", m_purity.get());
     dumpJsonBoolIf(str, "usePtr", usePtr());
     dumpJsonGen(str);
 }
-int AstCMethodHard::instrCount() const {
-    return 0;  // TODO
-}
-void AstCMethodHard::setPurity() {
+bool AstCMethodHard::getPurity() {
     if (method() == VCMethod::DYN_AT_WRITE_APPEND
         || method() == VCMethod::DYN_AT_WRITE_APPEND_BACK) {
-        m_pure = false;
         // Treat atWriteAppend as pure if the argument is a loop iterator
         if (const AstNodeExpr* const argp = pinsp()) {
             if (const AstVarRef* const varrefp = VN_CAST(argp, VarRef)) {
-                if (varrefp->varp()->isUsedLoopIdx()) m_pure = true;
+                if (varrefp->varp()->isUsedLoopIdx()) return true;
             }
         }
-        return;
+        return false;
     }
-    m_pure = method().isPure();
-    if (!m_pure) return;
-    if (!fromp()->isPure()) m_pure = false;
-    if (!m_pure) return;
+    if (!method().isPure()) return false;
+    if (!fromp()->isPure()) return false;
     for (AstNodeExpr* argp = pinsp(); argp; argp = VN_AS(argp->nextp(), NodeExpr)) {
-        if (!argp->isPure()) {
-            m_pure = false;
-            return;
-        }
+        if (!argp->isPure()) return false;
     }
+    return true;
+}
+int AstCMethodHard::instrCount() const {
+    return 0;  // TODO
 }
 void AstCReset::dump(std::ostream& str) const {
     Super::dump(str);