Fix $random not updating seed (#3238). [Julie Schwartz]

Changes

@@ -30,6 +30,7 @@ Verilator 4.217 devel
 * Fix VL_STREAML_FAST_QQI with 64 bit left-hand-side (#3232) (#3235)
 * Fix $sformat of inputs/outputs (#3236). [Adrien Le Masle]
 * Fix associative array foreach loop (#3229).
+* Fix $random not updating seed (#3238). [Julie Schwartz]
 * Fix splitting of _eval and other top level functions. [Geza Lore, Shunyao CAD]
 
 

include/verilated.cpp

@@ -337,11 +337,17 @@ WDataOutP VL_RANDOM_W(int obits, WDataOutP outwp) VL_MT_SAFE {
     return outwp;
 }
 
-IData VL_RANDOM_SEEDED_II(IData seed) VL_MT_SAFE {
+IData VL_RANDOM_SEEDED_II(IData& seedr) VL_MT_SAFE {
+    // $random - seed is a new seed to apply, then we return new seed
+    Verilated::threadContextp()->randSeed(static_cast<int>(seedr));
+    seedr = VL_RANDOM_I();
+    return VL_RANDOM_I();
+}
+IData VL_URANDOM_SEEDED_II(IData seed) VL_MT_SAFE {
+    // $urandom - seed is a new seed to apply
     Verilated::threadContextp()->randSeed(static_cast<int>(seed));
     return VL_RANDOM_I();
 }
-
 IData VL_RAND_RESET_I(int obits) VL_MT_SAFE {
     if (Verilated::threadContextp()->randReset() == 0) return 0;
     IData data = ~0;

include/verilated_funcs.h

@@ -85,7 +85,8 @@ extern void VL_DBG_MSGF(const char* formatp, ...) VL_ATTR_PRINTF(1) VL_MT_SAFE;
 inline IData VL_RANDOM_I() VL_MT_SAFE { return vl_rand64(); }
 inline QData VL_RANDOM_Q() VL_MT_SAFE { return vl_rand64(); }
 extern WDataOutP VL_RANDOM_W(int obits, WDataOutP outwp);
-extern IData VL_RANDOM_SEEDED_II(IData seed) VL_MT_SAFE;
+extern IData VL_RANDOM_SEEDED_II(IData& seedr) VL_MT_SAFE;
+extern IData VL_URANDOM_SEEDED_II(IData seed) VL_MT_SAFE;
 inline IData VL_URANDOM_RANGE_I(IData hi, IData lo) {
     const vluint64_t rnd = vl_rand64();
     if (VL_LIKELY(hi > lo)) {

src/V3AstNodes.h

@@ -5578,7 +5578,8 @@ public:
     }
     virtual string emitC() override {
         return m_reset ? "VL_RAND_RESET_%nq(%nw, %P)"
-               : seedp()  ? "VL_RANDOM_SEEDED_%nq%lq(%li)"
+                       : seedp() ? (urandom() ? "VL_URANDOM_SEEDED_%nq%lq(%li)"
+                                              : "VL_RANDOM_SEEDED_%nq%lq(%li)")
                                  : isWide() ? "VL_RANDOM_%nq(%nw, %P)"  //
                                             : "VL_RANDOM_%nq()";
     }

src/V3LinkLValue.cpp

@@ -183,6 +183,13 @@ private:
         VL_RESTORER(m_setRefLvalue);
         iterateChildren(nodep);
     }
+    virtual void visit(AstRand* nodep) override {
+        VL_RESTORER(m_setRefLvalue);
+        {
+            if (!nodep->urandom()) m_setRefLvalue = VAccess::WRITE;
+            iterateAndNextNull(nodep->seedp());
+        }
+    }
     virtual void visit(AstReadMem* nodep) override {
         VL_RESTORER(m_setRefLvalue);
         {

test_regress/t/t_sys_rand_seed.v

@@ -6,16 +6,39 @@
 
 module t;
 
+   integer seeda;
+   integer seedb;
+   integer seedc;
    int valuea;
    int valueb;
+   int valuec;
 
    initial begin
-      valuea = $random(10);
+      // $random unlike $urandom updates the value if given
-      valueb = $random(10);
+      seeda = 10;
+      valuea = $random(seeda);
+      seedb = 10;
+      valueb = $random(seedb);
       if (valuea !== valueb) $stop;
+
+      seeda = 10;
+      valuea = $random(seeda);
+      seedb = seeda;
+      valueb = $random(seedb);
+      seedc = seedb;
+      valuec = $random(seedc);
+      if (valuea == valueb && valueb == valuec) $stop;  // May false fail 1 in 1^64
+      if (seeda == seedb && seedb == seedc) $stop;  // May false fail 1 in 1^64
+       
       valuea = $urandom(10);
       valueb = $urandom(10);
       if (valuea !== valueb) $stop;
+
+      valuea = $urandom(10);
+      valueb = $urandom();
+      valuec = $urandom();
+      if (valuea == valueb && valueb == valuec) $stop;  // May false fail 1 in 1^64
+
       $write("*-* All Finished *-*\n");
       $finish;
    end