Internals: Break unnecessary dependencies in V3Order.

Signed-off-by: Wilson Snyder <wsnyder@wsnyder.org>

src/V3Ast.h

@@ -208,14 +208,37 @@ public:
 	    "COMBO","INITIAL","SETTLE","NEVER"
 	};
 	return names[m_e];
-    };
+    }
     const char* verilogKwd() const {
 	static const char* const names[] = {
 	    "%E-edge", "[any]", "edge", "posedge", "negedge", "[high]","[low]",
 	    "*","[initial]","[settle]","[never]"
 	};
 	return names[m_e];
-    };
+    }
+    // Return true iff this and the other have mutually exclusive transitions
+    bool exclusiveEdge(const AstEdgeType& other) const {
+        switch (m_e) {
+        case AstEdgeType::ET_POSEDGE:
+            switch (other.m_e) {
+            case AstEdgeType::ET_NEGEDGE:  // FALLTHRU
+            case AstEdgeType::ET_LOWEDGE:
+                return true;
+            default: {}
+            }
+            break;
+        case AstEdgeType::ET_NEGEDGE:
+            switch (other.m_e) {
+            case AstEdgeType::ET_POSEDGE:  // FALLTHRU
+            case AstEdgeType::ET_HIGHEDGE:
+                return true;
+            default: {}
+            }
+            break;
+        default: {}
+        }
+        return false;
+    }
     inline AstEdgeType () : m_e(ET_ILLEGAL) {}
     // cppcheck-suppress noExplicitConstructor
     inline AstEdgeType (en _e) : m_e(_e) {}

src/V3Order.cpp

@@ -562,6 +562,7 @@ private:
     void processMoveReadyOne(OrderMoveVertex* vertexp);
     void processMoveDoneOne(OrderMoveVertex* vertexp);
     void processMoveOne(OrderMoveVertex* vertexp, OrderMoveDomScope* domScopep, int level);
+    static bool domainsExclusive(const AstSenTree* fromp, const AstSenTree* top);
 
     string cfuncName(AstNodeModule* modp, AstSenTree* domainp, AstScope* scopep, AstNode* forWhatp) {
 	modp->user3Inc();
@@ -1350,6 +1351,41 @@ void OrderVisitor::processMoveBuildGraph() {
     }
 }
 
+bool OrderVisitor::domainsExclusive(const AstSenTree* fromp,
+                                    const AstSenTree* top) {
+    // Return 'true' if we can prove that both 'from' and 'to' cannot both
+    // be active on the same eval pass, or false if we can't prove this.
+    //
+    // For now, this only detects the case of 'always @(posedge clk)'
+    // and 'always @(negedge clk)' being exclusive.
+    //
+    // Are there any other cases we need to handle? Maybe not,
+    // because these are not exclusive:
+    //   always @(posedge A or posedge B)
+    //   always @(negedge A)
+    //
+    // ... unless you know more about A and B, which sounds hard.
+    const AstSenItem* fromSenListp = fromp->sensesp()->castSenItem();
+    const AstSenItem* toSenListp = top->sensesp()->castSenItem();
+    // If clk gating is ever reenabled, we may need to update this to handle
+    // AstSenGate also.
+    if (!fromSenListp) fromp->v3fatalSrc("sensitivity list item is not an AstSenItem");
+    if (!toSenListp) top->v3fatalSrc("sensitivity list item is not an AstSenItem");
+
+    if (fromSenListp->nextp()) return false;
+    if (toSenListp->nextp()) return false;
+
+    const AstNodeVarRef* fromVarrefp = fromSenListp->varrefp();
+    const AstNodeVarRef* toVarrefp = toSenListp->varrefp();
+    if (!fromVarrefp || !toVarrefp) return false;
+
+    // We know nothing about the relationship between different clocks here,
+    // so give up on proving anything.
+    if (fromVarrefp->varScopep() != toVarrefp->varScopep()) return false;
+
+    return fromSenListp->edgeType().exclusiveEdge(toSenListp->edgeType());
+}
+
 void OrderVisitor::processMoveBuildGraphIterate (OrderMoveVertex* moveVxp, V3GraphVertex* vertexp, int weightmin) {
     // Search forward from given logic vertex, making new edges based on moveVxp
     for (V3GraphEdge* edgep = vertexp->outBeginp(); edgep; edgep=edgep->outNextp()) {
@@ -1357,6 +1393,26 @@ void OrderVisitor::processMoveBuildGraphIterate (OrderMoveVertex* moveVxp, V3Gra
             int weight = weightmin;
             if (weight==0 || weight>edgep->weight()) weight=edgep->weight();
             if (OrderLogicVertex* toLVertexp = dynamic_cast<OrderLogicVertex*>(edgep->top())) {
+                //  "Initial" and "settle" domains run at time 0 and never
+                //  again. Everything else runs at time >0 and never before.
+                //  Ignore deps that cross the time-zero/nonzero boundary.
+                //  We'll never run both vertices in the same eval() pass
+                //  so there's no need to order them.
+                bool toInitial = (toLVertexp->domainp()->hasInitial()
+                                  || toLVertexp->domainp()->hasSettle());
+                bool fromInitial = (moveVxp->logicp()->domainp()->hasInitial()
+                                    || moveVxp->logicp()->domainp()->hasSettle());
+                if (toInitial != fromInitial) {
+                    continue;
+                }
+                // Sometimes we get deps between 'always @(posedge clk)' and
+                // 'always @(negedge clk)' domains. Discard these. We'll never
+                // evaluate both logic vertices on the same eval() pass so
+                // there's no need to order them.
+                if (domainsExclusive(moveVxp->logicp()->domainp(),
+                                     toLVertexp->domainp())) {
+                    continue;
+                }
                 // Path from vertexp to a logic vertex; new edge
                 // Note we use the last edge's weight, not some function of multiple edges
                 new OrderEdge(&m_pomGraph, moveVxp, toLVertexp->moveVxp(), weight);

test_regress/t/t_case_huge.pl

@@ -13,7 +13,7 @@ compile (
 
 if ($Self->{vlt}) {
     file_grep ($Self->{stats}, qr/Optimizations, Tables created\s+(\d+)/i, 10);
-    file_grep ($Self->{stats}, qr/Optimizations, Combined CFuncs\s+(\d+)/i, 9);
+    file_grep ($Self->{stats}, qr/Optimizations, Combined CFuncs\s+(\d+)/i, 8);
 }
 
 execute (

test_regress/t/t_inst_tree_inl0_pub1.pl

@@ -36,7 +36,7 @@ sub checkRelativeRefs {
 if ($Self->{vlt}) {
     # We expect to combine sequent functions across multiple instances of
     # l2, l3, l4, l5. If this number drops, please confirm this has not broken.
-    file_grep ($Self->{stats}, qr/Optimizations, Combined CFuncs\s+(\d+)/i, 59);
+    file_grep ($Self->{stats}, qr/Optimizations, Combined CFuncs\s+(\d+)/i, 52);
 
     # Expect absolute refs in CFuncs for t (top module) and l1 (because it
     # has only one instance)

test_regress/t/t_inst_tree_inl0_pub1_norelcfuncs.pl

@@ -16,7 +16,7 @@ compile (
 if ($Self->{vlt}) {
     # Fewer optimizations than t_inst_tree_inl0_pub1 which allows
     # relative CFuncs:
-    file_grep ($Self->{stats}, qr/Optimizations, Combined CFuncs\s+(\d+)/i, 16);
+    file_grep ($Self->{stats}, qr/Optimizations, Combined CFuncs\s+(\d+)/i, 31);
 
     # Should not find any 'this->' except some 'this->__VlSymsp'
     my @files = `ls $Self->{obj_dir}/*.cpp`;