Add STATICVAR warning and convert to automatic (#4027) (#4030)

Signed-off-by: Ryszard Rozak <rrozak@antmicro.com>

docs/guide/exe_verilator.rst

@@ -1517,7 +1517,7 @@ Summary:
    equivalent to ``-Wno-ALWCOMBORDER -Wno-BSSPACE -Wno-CASEINCOMPLETE
    -Wno-CASEOVERLAP -Wno-CASEX -Wno-CASTCONST -Wno-CASEWITHX -Wno-CMPCONST -Wno-COLONPLUS
    -Wno-IMPLICIT -Wno-IMPLICITSTATIC -Wno-LITENDIAN -Wno-PINCONNECTEMPTY
-   -Wno-PINMISSING -Wno-SYNCASYNCNET -Wno-UNDRIVEN -Wno-UNSIGNED
+   -Wno-PINMISSING -Wno-STATICVAR -Wno-SYNCASYNCNET -Wno-UNDRIVEN -Wno-UNSIGNED
    -Wno-UNUSEDGENVAR -Wno-UNUSEDPARAM -Wno-UNUSEDSIGNAL
    -Wno-WIDTH`` plus the list shown for Wno-style.
 

docs/guide/warnings.rst

@@ -1302,6 +1302,17 @@ List Of Warnings
    * The variable is tristate or bidirectional. (e.g., :code:`inout`).
 
 
+.. option:: STATICVAR
+
+   Warns that a static variable declared in a loop with declaration assignment
+   was converted to automatic. Often such variables were intended to
+   instead be declared "automatic".
+
+   Ignoring this warning may make Verilator differ from other simulators,
+   which will treat the variable as static. Verilator may in future versions also
+   treat the variable as static.
+
+
 .. option:: STMTDLY
 
    Warns that the code has a statement with a delayed time in front of it.

src/V3Error.h

@@ -131,6 +131,7 @@ public:
         SELRANGE,       // Selection index out of range
         SHORTREAL,      // Shortreal not supported
         SPLITVAR,       // Cannot split the variable
+        STATICVAR,      // Static variable declared in a loop with a declaration assignment
         STMTDLY,        // Delayed statement
         SYMRSVDWORD,    // Symbol is Reserved Word
         SYNCASYNCNET,   // Mixed sync + async reset
@@ -195,7 +196,7 @@ public:
             "MULTIDRIVEN", "MULTITOP", "NOLATCH", "NULLPORT", "PINCONNECTEMPTY",
             "PINMISSING", "PINNOCONNECT",  "PINNOTFOUND", "PKGNODECL", "PROCASSWIRE",
             "PROFOUTOFDATE", "PROTECTED", "RANDC", "REALCVT", "REDEFMACRO", "RISEFALLDLY",
-            "SELRANGE", "SHORTREAL", "SPLITVAR", "STMTDLY", "SYMRSVDWORD", "SYNCASYNCNET",
+            "SELRANGE", "SHORTREAL", "SPLITVAR", "STATICVAR", "STMTDLY", "SYMRSVDWORD", "SYNCASYNCNET",
             "TICKCOUNT", "TIMESCALEMOD",
             "UNDRIVEN", "UNOPT", "UNOPTFLAT", "UNOPTTHREADS",
             "UNPACKED", "UNSIGNED", "UNUSEDGENVAR", "UNUSEDPARAM", "UNUSEDSIGNAL",
@@ -231,8 +232,8 @@ public:
                 || m_e == CASEOVERLAP || m_e == CASEWITHX || m_e == CASEX || m_e == CASTCONST
                 || m_e == CMPCONST || m_e == COLONPLUS || m_e == IMPLICIT || m_e == IMPLICITSTATIC
                 || m_e == LATCH || m_e == LITENDIAN || m_e == PINMISSING || m_e == REALCVT
-                || m_e == UNSIGNED || m_e == WIDTH || m_e == WIDTHTRUNC || m_e == WIDTHEXPAND
-                || m_e == WIDTHXZEXPAND);
+                || m_e == STATICVAR || m_e == UNSIGNED || m_e == WIDTH || m_e == WIDTHTRUNC
+                || m_e == WIDTHEXPAND || m_e == WIDTHXZEXPAND);
     }
     // Warnings that are style only
     bool styleError() const VL_MT_SAFE {

src/V3LinkParse.cpp

@@ -223,8 +223,10 @@ private:
 
     void visit(AstVar* nodep) override {
         cleanFileline(nodep);
-        if (nodep->lifetime().isStatic() && m_insideLoop) {
-            nodep->v3warn(E_UNSUPPORTED, "Unsupported: Static variable inside a loop");
+        if (nodep->lifetime().isStatic() && m_insideLoop && nodep->valuep()) {
+            nodep->lifetime(VLifetime::AUTOMATIC);
+            nodep->v3warn(STATICVAR, "Static variable with assignment declaration declared in a "
+                                     "loop converted to automatic");
         }
         if (nodep->lifetime().isNone() && nodep->varType() != VVarType::PORT) {
             nodep->lifetime(m_lifetime);

test_regress/t/t_static_in_loop_unsup.out

@@ -1,5 +1,6 @@
-%Error-UNSUPPORTED: t/t_static_in_loop_unsup.v:14:24: Unsupported: Static variable inside a loop
+%Warning-STATICVAR: t/t_static_in_loop_unsup.v:14:24: Static variable with assignment declaration declared in a loop converted to automatic
    14 |             static int a = 0;
       |                        ^
-                    ... For error description see https://verilator.org/warn/UNSUPPORTED?v=latest
+                    ... For warning description see https://verilator.org/warn/STATICVAR?v=latest
+                    ... Use "/* verilator lint_off STATICVAR */" and lint_on around source to disable this message.
 %Error: Exiting due to