Handle tail recursion in CevalFunction

This fixes ticket:4838

Belonging to [master]:
  - OpenModelica/OMCompiler#2300
  - OpenModelica/OpenModelica-testsuite#889

Author: sjoelund

Compiler/FrontEnd/CevalFunction.mo

@@ -1031,12 +1031,16 @@ algorithm
       FCore.Graph env;
       DAE.Exp lhs, rhs, condition;
       DAE.ComponentRef lhs_cref;
-      Values.Value rhs_val;
+      Values.Value rhs_val, v;
       list<DAE.Exp> exps;
       list<Values.Value> vals;
       list<DAE.Statement> statements;
       Absyn.Path path;
+      DAE.Type returnType;
       LoopControl loop_ctrl;
+      DAE.TailCall tailCall;
+      String var;
+      list<String> vars;
 
     case (DAE.STMT_ASSIGN(exp1 = lhs, exp = rhs), cache, env)
       equation
@@ -1100,12 +1104,29 @@ algorithm
       then
         (cache, inEnv, NEXT());
     // Special case for print, and other known calls for now; evaluated even when there is no ST
-    case (DAE.STMT_NORETCALL(exp = rhs as DAE.CALL(path = path, expLst = exps)), _, _)
+    case (DAE.STMT_NORETCALL(exp = rhs as DAE.CALL(path = path, expLst = exps, attr=DAE.CALL_ATTR(ty=returnType, tailCall=tailCall))), _, _)
       algorithm
         (cache, vals) := cevalExpList(exps, inCache, inEnv);
-        (cache, _) := cevalExp(rhs, cache, inEnv);
+        (cache, v) := cevalExp(rhs, cache, inEnv);
+        (cache, env, outLoopControl) := match tailCall
+          case DAE.NO_TAIL() then (cache, inEnv, NEXT());
+          // Handle tail recursion; same as a assigning all outputs followed by a return
+          case DAE.TAIL(outVars={}) then (cache, inEnv, RETURN());
+          case DAE.TAIL(outVars={var})
+            algorithm
+              (cache, env) := assignVariable(ComponentReference.makeUntypedCrefIdent(var), v, cache, inEnv);
+            then (cache, env, RETURN());
+          case DAE.TAIL(outVars=vars)
+            algorithm
+              Values.TUPLE(vals) := v;
+              for val in vals loop
+                var::vars := vars;
+                (cache, env) := assignVariable(ComponentReference.makeUntypedCrefIdent(var), val, cache, inEnv);
+              end for;
+            then (cache, env, RETURN());
+        end match;
       then
-        (cache, inEnv, NEXT());
+        (cache, env, NEXT());
 
     case (DAE.STMT_RETURN(), _, _)
       then

Compiler/FrontEnd/DAE.mo

@@ -1534,6 +1534,7 @@ public uniontype TailCall
   end NO_TAIL;
   record TAIL
     list<String> vars;
+    list<String> outVars;
   end TAIL;
 end TailCall;
 

Compiler/FrontEnd/DAEDump.mo

@@ -1462,8 +1462,15 @@ algorithm
         ();
 
     case (DAE.STMT_NORETCALL(exp = e1),i)
-      equation
+      algorithm
         indent(i);
+        _ := match e1
+          case DAE.CALL(attr=DAE.CALL_ATTR(tailCall=DAE.TAIL()))
+            algorithm
+              Print.printBuf("return ");
+            then ();
+          else ();
+        end match;
         ExpressionDump.printExp(e1);
         Print.printBuf(";\n");
       then
@@ -1716,8 +1723,12 @@ algorithm
     case (DAE.STMT_NORETCALL(exp = e),i)
       equation
         s1 = indentStr(i);
-        s2 = ExpressionDump.printExpStr(e);
-        str = stringAppendList({s1,s2,";\n"});
+        s2 = match e
+          case DAE.CALL(attr=DAE.CALL_ATTR(tailCall=DAE.TAIL())) then "return ";
+          else "";
+        end match;
+        s3 = ExpressionDump.printExpStr(e);
+        str = stringAppendList({s1,s2,s3,";\n"});
       then
         str;
 

Compiler/FrontEnd/InstUtil.mo

@@ -7551,13 +7551,13 @@ protected function optimizeStatementTail2
   output DAE.Exp orhs;
 algorithm
   true:=valueEq(lhsVars,outvars);
-  (orhs,true) := optimizeStatementTail3(path,rhs,invars,source);
+  (orhs,true) := optimizeStatementTail3(path,rhs,invars,lhsVars,source);
 end optimizeStatementTail2;
 
 protected function optimizeStatementTail3
   input Absyn.Path path;
   input DAE.Exp rhs;
-  input list<String> vars;
+  input list<String> vars, lhsVars;
   input DAE.ElementSource source;
   output DAE.Exp orhs;
   output Boolean isTailRecursive;
@@ -7585,18 +7585,18 @@ algorithm
         if Flags.isSet(Flags.TAIL) then
           Error.addSourceMessage(Error.COMPILER_NOTIFICATION,{str},ElementSource.getElementSourceFileInfo(source));
         end if;
-        attr.tailCall = DAE.TAIL(vars);
+        attr.tailCall = DAE.TAIL(vars,lhsVars);
         call.attr = attr;
       then (call,true);
     case (_,DAE.IFEXP(e1,e2,e3),_,_)
       equation
-        (e2,b1) = optimizeStatementTail3(path,e2,vars,source);
-        (e3,b2) = optimizeStatementTail3(path,e3,vars,source);
+        (e2,b1) = optimizeStatementTail3(path,e2,vars,lhsVars,source);
+        (e3,b2) = optimizeStatementTail3(path,e3,vars,lhsVars,source);
         true = b1 or b2;
       then (DAE.IFEXP(e1,e2,e3),true);
     case (_,DAE.MATCHEXPRESSION(matchType as DAE.MATCH(_) /*TODO:matchcontinue*/,inputs,aliases,localDecls,cases,et),_,_)
       equation
-        cases = optimizeStatementTailMatchCases(path,cases,false,{},vars,source);
+        cases = optimizeStatementTailMatchCases(path,cases,false,{},vars,lhsVars,source);
       then (DAE.MATCHEXPRESSION(matchType,inputs,aliases,localDecls,cases,et),true);
     else (rhs,false);
   end matchcontinue;
@@ -7607,7 +7607,7 @@ protected function optimizeStatementTailMatchCases
   input list<DAE.MatchCase> inCases;
   input Boolean changed;
   input list<DAE.MatchCase> inAcc;
-  input list<String> vars;
+  input list<String> vars, lhsVars;
   input DAE.ElementSource source;
   output list<DAE.MatchCase> ocases;
 algorithm
@@ -7627,18 +7627,18 @@ algorithm
     case (_,{},true,acc,_,_) then listReverse(acc);
     case (_,DAE.CASE(patterns,patternGuard,localDecls,body,SOME(exp),resultInfo,jump,info)::cases,_,acc,_,_)
       equation
-        (exp,true) = optimizeStatementTail3(path,exp,vars,source);
+        (exp,true) = optimizeStatementTail3(path,exp,vars,lhsVars,source);
         case_ = DAE.CASE(patterns,patternGuard,localDecls,body,SOME(exp),resultInfo,jump,info);
-      then optimizeStatementTailMatchCases(path,cases,true,case_::acc,vars,source);
+      then optimizeStatementTailMatchCases(path,cases,true,case_::acc,vars,lhsVars,source);
     case (_,DAE.CASE(patterns,patternGuard,localDecls,body,SOME(DAE.TUPLE({})),resultInfo,jump,info)::cases,_,acc,_,_)
       equation
         DAE.STMT_NORETCALL(exp,sourceStmt) = List.last(body);
-        (exp,true) = optimizeStatementTail3(path,exp,vars,source);
+        (exp,true) = optimizeStatementTail3(path,exp,vars,lhsVars,source);
         body = List.set(body,listLength(body),DAE.STMT_NORETCALL(exp,sourceStmt));
         case_ = DAE.CASE(patterns,patternGuard,localDecls,body,SOME(DAE.TUPLE({})),resultInfo,jump,info);
-      then optimizeStatementTailMatchCases(path,cases,true,case_::acc,vars,source);
+      then optimizeStatementTailMatchCases(path,cases,true,case_::acc,vars,lhsVars,source);
     case (_,case_::cases,_,acc,_,_)
-      then optimizeStatementTailMatchCases(path,cases,changed,case_::acc,vars,source);
+      then optimizeStatementTailMatchCases(path,cases,changed,case_::acc,vars,lhsVars,source);
   end matchcontinue;
 end optimizeStatementTailMatchCases;
 

Compiler/Template/DAEDumpTV.mo

@@ -1391,6 +1391,20 @@ package DAE
   end SUM;
 
   end Exp;
+
+  uniontype CallAttributes
+    record CALL_ATTR
+      TailCall tailCall "Input variables of the function if the call is tail-recursive";
+    end CALL_ATTR;
+  end CallAttributes;
+
+  uniontype TailCall
+    record NO_TAIL
+    end NO_TAIL;
+    record TAIL
+    end TAIL;
+  end TailCall;
+
 end DAE;
 
 package SCodeDump

Compiler/Template/DAEDumpTpl.tpl

@@ -698,8 +698,11 @@ template dumpNoRetCall(DAE.Exp call_exp, DAE.ElementSource src)
 ::=
   let call_str = dumpExp(call_exp)
   let src_str = dumpSource(src)
+  let tail_str = match call_exp
+    case CALL(attr=CALL_ATTR(tailCall=TAIL(__))) then "return "
+    else ""
   <<
-  <%call_str%><%src_str%>;
+  <%tail_str%><%call_str%><%src_str%>;
   >>
 end dumpNoRetCall;