some minor ZAM optimization improvements

src/Expr.cc

@@ -4377,6 +4377,12 @@ bool ListExpr::IsPure() const {
     return true;
 }
 
+bool ListExpr::HasConstantOps() const {
+    loop_over_list(exprs, i) if ( exprs[i]->Tag() != EXPR_CONST ) return false;
+
+    return true;
+}
+
 ValPtr ListExpr::Eval(Frame* f) const {
     std::vector<ValPtr> evs;
 

src/Expr.h

@@ -1273,6 +1273,10 @@ public:
     // Optimization-related:
     ExprPtr Duplicate() override;
 
+    bool IsReduced(Reducer* c) const override;
+    bool WillTransform(Reducer* c) const override;
+    ExprPtr Reduce(Reducer* c, StmtPtr& red_stmt) override;
+
     const std::vector<int>& Map() const { return map; }
 
 protected:
@@ -1362,7 +1366,9 @@ public:
     // Optimization-related:
     ExprPtr Duplicate() override;
 
+    bool IsReduced(Reducer* c) const override;
     bool HasReducedOps(Reducer* c) const override;
+    ExprPtr Reduce(Reducer* c, StmtPtr& red_stmt) override;
 
 protected:
     ValPtr Fold(Val* v1, Val* v2) const override;
@@ -1485,6 +1491,9 @@ public:
     // True if the entire list represents pure values.
     bool IsPure() const override;
 
+    // True if the entire list represents constant values.
+    bool HasConstantOps() const;
+
     ValPtr Eval(Frame* f) const override;
 
     TypePtr InitType() const override;

src/script_opt/Expr.cc

@@ -83,6 +83,11 @@ const RecordCoerceExpr* Expr::AsRecordCoerceExpr() const {
     return (const RecordCoerceExpr*)this;
 }
 
+RecordConstructorExpr* Expr::AsRecordConstructorExpr() {
+    CHECK_TAG(tag, EXPR_RECORD_CONSTRUCTOR, "ExprVal::AsRecordConstructorExpr", expr_name)
+    return (RecordConstructorExpr*)this;
+}
+
 const RecordConstructorExpr* Expr::AsRecordConstructorExpr() const {
     CHECK_TAG(tag, EXPR_RECORD_CONSTRUCTOR, "ExprVal::AsRecordConstructorExpr", expr_name)
     return (const RecordConstructorExpr*)this;
@@ -502,6 +507,11 @@ ExprPtr BinaryExpr::Reduce(Reducer* c, StmtPtr& red_stmt) {
     red_stmt = MergeStmts(red_stmt, std::move(red2_stmt));
 
     auto op1_fold_val = op1->FoldVal();
+
+    if ( ! op1_fold_val && op1->Tag() == EXPR_LIST && op1->AsListExpr()->HasConstantOps() )
+        // We can turn the list into a ListVal.
+        op1_fold_val = op1->Eval(nullptr);
+
     auto op2_fold_val = op2->FoldVal();
     if ( op1_fold_val && op2_fold_val ) {
         auto fold = Fold(op1_fold_val.get(), op2_fold_val.get());
@@ -1909,6 +1919,27 @@ ExprPtr RecordCoerceExpr::Duplicate() {
     return SetSucc(new RecordCoerceExpr(op_dup, GetType<RecordType>()));
 }
 
+bool RecordCoerceExpr::IsReduced(Reducer* c) const {
+    if ( WillTransform(c) )
+        return NonReduced(this);
+
+    return UnaryExpr::IsReduced(c);
+}
+
+bool RecordCoerceExpr::WillTransform(Reducer* c) const { return op->Tag() == EXPR_RECORD_CONSTRUCTOR; }
+
+ExprPtr RecordCoerceExpr::Reduce(Reducer* c, StmtPtr& red_stmt) {
+    if ( WillTransform(c) ) {
+        auto rt = cast_intrusive<RecordType>(type);
+        auto rc_op = op->AsRecordConstructorExpr();
+        auto known_constr = make_intrusive<RecordConstructorExpr>(rt, rc_op->Op());
+        auto red_e = known_constr->Reduce(c, red_stmt);
+        return TransformMe(std::move(red_e), c, red_stmt);
+    }
+
+    return UnaryExpr::Reduce(c, red_stmt);
+}
+
 ExprPtr TableCoerceExpr::Duplicate() {
     auto op_dup = op->Duplicate();
     return SetSucc(new TableCoerceExpr(op_dup, GetType<TableType>()));
@@ -1979,8 +2010,22 @@ ExprPtr InExpr::Duplicate() {
     return SetSucc(new InExpr(op1_d, op2_d));
 }
 
+bool InExpr::IsReduced(Reducer* c) const {
+    if ( op2->Tag() == EXPR_SET_CONSTRUCTOR && op2->GetOp1()->AsListExpr()->HasConstantOps() )
+        return NonReduced(this);
+
+    return BinaryExpr::IsReduced(c);
+}
+
 bool InExpr::HasReducedOps(Reducer* c) const { return op1->HasReducedOps(c) && op2->IsSingleton(c); }
 
+ExprPtr InExpr::Reduce(Reducer* c, StmtPtr& red_stmt) {
+    if ( op2->Tag() == EXPR_SET_CONSTRUCTOR && op2->GetOp1()->AsListExpr()->HasConstantOps() )
+        op2 = make_intrusive<ConstExpr>(op2->Eval(nullptr));
+
+    return BinaryExpr::Reduce(c, red_stmt);
+}
+
 ExprPtr CallExpr::Duplicate() {
     auto func_d = func->Duplicate();
     auto args_d = args->Duplicate()->AsListExprPtr();

src/script_opt/ZAM/AM-Opt.cc

@@ -228,6 +228,14 @@ bool ZAMCompiler::PruneUnused() {
             continue;
         }
 
+        if ( i == insts1.size() - 1 && inst->op == OP_RETURN_X ) {
+            // A non-value return at the very end of the body
+            // doesn't actually do anything.
+            did_prune = true;
+            KillInst(i);
+            continue;
+        }
+
         if ( inst->IsLoad() && ! VarIsUsed(inst->v1) ) {
             did_prune = true;
             KillInst(i);