Move Concat balancing from DFG to FuncOpt

This means it applies more widely, e.g. inside sequential logic.

docs/guide/exe_verilator.rst

@@ -591,6 +591,8 @@ Summary:
 
 .. option:: -fno-func-opt
 
+.. option:: -fno-func-opt-balance-cat
+
 .. option:: -fno-func-opt-split-cat
 
 .. option:: -fno-gate

src/CMakeLists.txt

@@ -225,7 +225,6 @@ set(COMMON_SOURCES
     V3Descope.cpp
     V3Dfg.cpp
     V3DfgAstToDfg.cpp
-    V3DfgBalanceTrees.cpp
     V3DfgCache.cpp
     V3DfgDecomposition.cpp
     V3DfgDfgToAst.cpp

src/Makefile_obj.in

@@ -238,7 +238,6 @@ RAW_OBJS_PCH_ASTNOMT = \
 	V3Descope.o \
 	V3Dfg.o \
 	V3DfgAstToDfg.o \
-	V3DfgBalanceTrees.o \
 	V3DfgCache.o \
 	V3DfgDecomposition.o \
 	V3DfgDfgToAst.o \

src/V3Dfg.h

@@ -274,9 +274,6 @@ class DfgVertex VL_NOT_FINAL {
     // Predicate: has 1 or more sinks
     bool hasSinks() const { return m_sinksp != nullptr; }
 
-    // Predicate: has precisely 1 sink
-    bool hasSingleSink() const { return m_sinksp && !m_sinksp->m_nextp; }
-
     // Predicate: has 2 or more sinks
     bool hasMultipleSinks() const { return m_sinksp && m_sinksp->m_nextp; }
 

src/V3DfgOptimizer.cpp

@@ -236,7 +236,7 @@ void V3DfgOptimizer::extract(AstNetlist* netlistp) {
     V3Global::dumpCheckGlobalTree("dfg-extract", 0, dumpTreeEitherLevel() >= 3);
 }
 
-void V3DfgOptimizer::optimize(AstNetlist* netlistp, const string& label, bool lastInvocation) {
+void V3DfgOptimizer::optimize(AstNetlist* netlistp, const string& label) {
     UINFO(2, __FUNCTION__ << ": " << endl);
 
     // NODE STATE
@@ -282,7 +282,7 @@ void V3DfgOptimizer::optimize(AstNetlist* netlistp, const string& label, bool la
         for (auto& component : acyclicComponents) {
             if (dumpDfgLevel() >= 7) component->dumpDotFilePrefixed(ctx.prefix() + "source");
             // Optimize the component
-            V3DfgPasses::optimize(*component, ctx, lastInvocation);
+            V3DfgPasses::optimize(*component, ctx);
             // Add back under the main DFG (we will convert everything back in one go)
             dfg->addGraph(*component);
         }

src/V3DfgOptimizer.h

@@ -29,7 +29,7 @@ namespace V3DfgOptimizer {
 void extract(AstNetlist*) VL_MT_DISABLED;
 
 // Optimize the design
-void optimize(AstNetlist*, const string& label, bool lastInvocation) VL_MT_DISABLED;
+void optimize(AstNetlist*, const string& label) VL_MT_DISABLED;
 }  // namespace V3DfgOptimizer
 
 #endif  // Guard

src/V3DfgPasses.cpp

@@ -42,11 +42,6 @@ V3DfgEliminateVarsContext::~V3DfgEliminateVarsContext() {
                      m_varsRemoved);
 }
 
-V3DfgBalanceTreesContext::~V3DfgBalanceTreesContext() {
-    V3Stats::addStat("Optimizations, DFG " + m_label + " BalanceTrees, concat trees balanced",
-                     m_balancedConcats);
-}
-
 static std::string getPrefix(const std::string& label) {
     if (label.empty()) return "";
     std::string str = VString::removeWhitespace(label);
@@ -337,7 +332,7 @@ void V3DfgPasses::eliminateVars(DfgGraph& dfg, V3DfgEliminateVarsContext& ctx) {
     for (AstVar* const varp : replacedVariables) varp->unlinkFrBack()->deleteTree();
 }
 
-void V3DfgPasses::optimize(DfgGraph& dfg, V3DfgOptimizationContext& ctx, bool lastInvocation) {
+void V3DfgPasses::optimize(DfgGraph& dfg, V3DfgOptimizationContext& ctx) {
     // There is absolutely nothing useful we can do with a graph of size 2 or less
     if (dfg.size() <= 2) return;
 
@@ -365,10 +360,6 @@ void V3DfgPasses::optimize(DfgGraph& dfg, V3DfgOptimizationContext& ctx, bool la
     }
     // Accumulate patterns for reporting
     if (v3Global.opt.stats()) ctx.m_patternStats.accumulate(dfg);
-    // The peephole pass covnerts all trees to right leaning, so only do this on the last DFG run.
-    if (lastInvocation) {
-        apply(4, "balanceTrees", [&]() { balanceTrees(dfg, ctx.m_balanceTreesContext); });
-    }
     apply(4, "regularize", [&]() { regularize(dfg, ctx.m_regularizeContext); });
     if (dumpDfgLevel() >= 8) dfg.dumpDotAllVarConesPrefixed(ctx.prefix() + "optimized");
 }

src/V3DfgPasses.h

@@ -68,17 +68,6 @@ class V3DfgEliminateVarsContext final {
     ~V3DfgEliminateVarsContext() VL_MT_DISABLED;
 };
 
-class V3DfgBalanceTreesContext final {
-    const std::string m_label;  // Label to apply to stats
-
-public:
-    VDouble0 m_balancedConcats;  // Number of temporaries introduced
-
-    explicit V3DfgBalanceTreesContext(const std::string& label)
-        : m_label{label} {}
-    ~V3DfgBalanceTreesContext() VL_MT_DISABLED;
-};
-
 class V3DfgOptimizationContext final {
     const std::string m_label;  // Label to add to stats, etc.
     const std::string m_prefix;  // Prefix to add to file dumps (derived from label)
@@ -103,7 +92,6 @@ class V3DfgOptimizationContext final {
     V3DfgPeepholeContext m_peepholeContext{m_label};
     V3DfgRegularizeContext m_regularizeContext{m_label};
     V3DfgEliminateVarsContext m_eliminateVarsContext{m_label};
-    V3DfgBalanceTreesContext m_balanceTreesContext{m_label};
 
     V3DfgPatternStats m_patternStats;
 
@@ -124,7 +112,7 @@ namespace V3DfgPasses {
 DfgGraph* astToDfg(AstModule&, V3DfgOptimizationContext&) VL_MT_DISABLED;
 
 // Optimize the given DfgGraph
-void optimize(DfgGraph&, V3DfgOptimizationContext&, bool lastInvocation) VL_MT_DISABLED;
+void optimize(DfgGraph&, V3DfgOptimizationContext&) VL_MT_DISABLED;
 
 // Convert DfgGraph back into Ast, and insert converted graph back into its parent module.
 // Returns the parent module.
@@ -146,8 +134,6 @@ void regularize(DfgGraph&, V3DfgRegularizeContext&) VL_MT_DISABLED;
 void removeUnused(DfgGraph&) VL_MT_DISABLED;
 // Eliminate (remove or replace) redundant variables. Also removes resulting unused logic.
 void eliminateVars(DfgGraph&, V3DfgEliminateVarsContext&) VL_MT_DISABLED;
-// Make computation trees balanced
-void balanceTrees(DfgGraph&, V3DfgBalanceTreesContext&) VL_MT_DISABLED;
 
 }  // namespace V3DfgPasses