Optimize duplicate JumpBlocks away (#4028)

src/V3AstNodeOther.h

@@ -2779,7 +2779,7 @@ public:
     bool isFirstInMyListOfStatements(AstNode* n) const override { return n == stmtsp(); }
 };
 class AstJumpBlock final : public AstNodeStmt {
-    // Block of code including a JumpGo and JumpLabel
+    // Block of code including a single JumpLabel, and 0+ JumpGo's to that label
     // Parents:  {statement list}
     // Children: {statement list, with JumpGo and JumpLabel below}
     // @astgen op1 := stmtsp : List[AstNode]

src/V3Const.cpp

@@ -3207,7 +3207,7 @@ private:
 
     void visit(AstJumpGo* nodep) override {
         iterateChildren(nodep);
-        // Jump to label where label immediately follows label is not useful
+        // Jump to label where label immediately follows this go is not useful
         if (nodep->labelp() == VN_CAST(nodep->nextp(), JumpLabel)) {
             VL_DO_DANGLING(nodep->unlinkFrBack()->deleteTree(), nodep);
             // Keep the label, might be other jumps pointing to it, gets cleaned later

src/V3LinkJump.cpp

@@ -35,6 +35,7 @@
 #include "V3LinkJump.h"
 
 #include "V3Ast.h"
+#include "V3AstUserAllocator.h"
 #include "V3Global.h"
 
 #include <algorithm>
@@ -46,6 +47,12 @@ VL_DEFINE_DEBUG_FUNCTIONS;
 
 class LinkJumpVisitor final : public VNVisitor {
 private:
+    // NODE STATE
+    //  AstNode::user1()    -> AstJumpLabel*, for this block if endOfIter
+    //  AstNode::user2()    -> AstJumpLabel*, for this block if !endOfIter
+    const VNUser1InUse m_user1InUse;
+    const VNUser2InUse m_user2InUse;
+
     // STATE
     AstNodeModule* m_modp = nullptr;  // Current module
     AstNodeFTask* m_ftaskp = nullptr;  // Current function/task
@@ -61,6 +68,13 @@ private:
         UINFO(4, "Create label for " << nodep << endl);
         if (VN_IS(nodep, JumpLabel)) return VN_AS(nodep, JumpLabel);  // Done
 
+        // Made it previously?  We always jump to the end, so this works out
+        if (endOfIter) {
+            if (nodep->user1p()) return VN_AS(nodep->user1p(), JumpLabel);
+        } else {
+            if (nodep->user2p()) return VN_AS(nodep->user2p(), JumpLabel);
+        }
+
         AstNode* underp = nullptr;
         bool under_and_next = true;
         if (VN_IS(nodep, NodeBlock)) {
@@ -125,6 +139,11 @@ private:
             }
             // Label goes last
             blockp->addEndStmtsp(labelp);
+            if (endOfIter) {
+                nodep->user1p(labelp);
+            } else {
+                nodep->user2p(labelp);
+            }
             return labelp;
         }
     }

src/V3Simulate.h

@@ -103,7 +103,7 @@ private:
     bool m_isOutputter;  // Creates output
     int m_instrCount;  ///< Number of nodes
     int m_dataCount;  ///< Bytes of data
-    AstJumpGo* m_jumpp;  ///< Jump label we're branching from
+    AstJumpGo* m_jumpp = nullptr;  ///< Jump label we're branching from
     // Simulating:
     std::unordered_map<const AstNodeDType*, std::deque<AstConst*>>
         m_constps;  ///< Lists of all AstConst* allocated per dtype

test_regress/t/t_debug_emitv.out

@@ -337,14 +337,12 @@ module Vt_debug_emitv_sub;
     function f;
         input signed int [31:0]  v;
         begin : label0
-            begin : label0
+            if ((v == 'sh0)) begin
-                if ((v == 'sh0)) begin
+                f = 'sh21;
-                    f = 'sh21;
-                    disable label0;
-                end
-                f = ({32'h1{{31'h0, v[2]}}} + 32'h1);
                 disable label0;
             end
+            f = ({32'h1{{31'h0, v[2]}}} + 32'h1);
+            disable label0;
         end
     endfunction
     signed real r;