From: Austin Clements <aclements@csail.mit.edu>
Date: Mon, 10 Aug 2009 23:27:54 +0000 (-0700)
Subject: Implement switch statement.  Can now extract effects from
X-Git-Tag: weekly.2009-11-06~919
X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=64193fcaa2f7351e83f3bc7fd40ac8def2148834;p=gostls13.git

Implement switch statement.  Can now extract effects from
non-addressable expressions.

R=rsc
APPROVED=rsc
DELTA=241  (202 added, 15 deleted, 24 changed)
OCL=32790
CL=32995
---

diff --git a/usr/austin/eval/expr.go b/usr/austin/eval/expr.go
index 4988224739..6168dfc417 100644
--- a/usr/austin/eval/expr.go
+++ b/usr/austin/eval/expr.go
@@ -546,6 +546,10 @@ func (a *exprCompiler) DoFloatLit(x *ast.FloatLit) {
 }
 
 func (a *exprCompiler) doString(s string) {
+	// Ideal strings don't have a named type but they are
+	// compatible with type string.
+
+	// TODO(austin) Use unnamed string type.
 	a.t = StringType;
 	a.evalString = func(*Frame) string { return s };
 }
@@ -678,7 +682,10 @@ func (a *exprCompiler) DoSelectorExpr(x *ast.SelectorExpr) {
 		// If it's a struct type, check fields and embedded types
 		var builder func(*exprCompiler);
 		if t, ok := t.(*StructType); ok {
-			for i, f := range t.Elems {
+			// TODO(austin) Work around := range bug
+			var i int;
+			var f StructField;
+			for i, f = range t.Elems {
 				var this *exprCompiler;
 				var sub func(*exprCompiler);
 				switch {
@@ -1465,31 +1472,47 @@ func (a *compiler) compileExpr(b *block, expr ast.Expr, constant bool) *exprComp
 // extractEffect separates out any effects that the expression may
 // have, returning a function that will perform those effects and a
 // new exprCompiler that is guaranteed to be side-effect free.  These
-// are the moral equivalents of "temp := &expr" and "*temp".  Because
-// this creates a temporary variable, the caller should create a
-// temporary block for the compilation of this expression and the
-// evaluation of the results.
-//
-// Implementation limit: The expression must be addressable.
-func (a *exprCompiler) extractEffect() (func(f *Frame), *exprCompiler) {
-	if a.evalAddr == nil {
-		// This is a much easier case, but the code is
-		// completely different.
-		log.Crash("extractEffect only implemented for addressable expressions");
-	}
-
-	// Create temporary
+// are the moral equivalents of "temp := expr" and "temp" (or "temp :=
+// &expr" and "*temp" for addressable exprs).  Because this creates a
+// temporary variable, the caller should create a temporary block for
+// the compilation of this expression and the evaluation of the
+// results.
+func (a *exprCompiler) extractEffect(errOp string) (func(f *Frame), *exprCompiler) {
+	// Create "&a" if a is addressable
+	rhs := a;
+	if a.evalAddr != nil {
+		rhs = a.copy();
+		rhs.t = NewPtrType(a.t);
+		rhs.genUnaryAddrOf(a);
+	}
+
+	// Create temp
 	tempBlock := a.block;
-	tempType := NewPtrType(a.t);
+	ac, ok := a.checkAssign(a.pos, []*exprCompiler{rhs}, errOp, "");
+	if !ok {
+		return nil, nil;
+	}
+	if len(ac.rmt.Elems) != 1 {
+		a.diag("multi-valued expression not allowed in %s", errOp);
+		return nil, nil;
+	}
+	tempType := ac.rmt.Elems[0];
+	if tempType.isIdeal() {
+		// It's too bad we have to duplicate this rule.
+		switch {
+		case tempType.isInteger():
+			tempType = IntType;
+		case tempType.isFloat():
+			tempType = FloatType;
+		default:
+			log.Crashf("unexpected ideal type %v", tempType);
+		}
+	}
 	temp := tempBlock.DefineSlot(tempType);
 	tempIdx := temp.Index;
 
-	// Generate "temp := &e"
-	addr := a.copy();
-	addr.t = tempType;
-	addr.genUnaryAddrOf(a);
-
-	assign := a.compileAssign(a.pos, tempType, []*exprCompiler{addr}, "", "");
+	// Create "temp := rhs"
+	assign := ac.compile(tempType);
 	if assign == nil {
 		log.Crashf("compileAssign type check failed");
 	}
@@ -1500,15 +1523,17 @@ func (a *exprCompiler) extractEffect() (func(f *Frame), *exprCompiler) {
 		assign(tempVal, f);
 	};
 
-	// Generate "*temp"
+	// Generate "temp" or "*temp"
 	getTemp := a.copy();
 	getTemp.t = tempType;
 	getTemp.genIdentOp(0, tempIdx);
+	if a.evalAddr == nil {
+		return effect, getTemp;
+	}
 
 	deref := a.copy();
 	deref.t = a.t;
 	deref.genStarOp(getTemp);
-
 	return effect, deref;
 }
 
diff --git a/usr/austin/eval/stmt.go b/usr/austin/eval/stmt.go
index 2bd7f8574e..2b401a1ba5 100644
--- a/usr/austin/eval/stmt.go
+++ b/usr/austin/eval/stmt.go
@@ -394,23 +394,26 @@ func (a *stmtCompiler) DoIncDecStmt(s *ast.IncDecStmt) {
 		return;
 	}
 
-	effect, l := l.extractEffect();
-
-	one := l.copy();
-	one.pos = s.Pos();
-	one.t = IdealIntType;
-	one.evalIdealInt = func() *bignum.Integer { return bignum.Int(1) };
-
 	var op token.Token;
+	var desc string;
 	switch s.Tok {
 	case token.INC:
 		op = token.ADD;
+		desc = "increment statement";
 	case token.DEC:
 		op = token.SUB;
+		desc = "decrement statement";
 	default:
 		log.Crashf("Unexpected IncDec token %v", s.Tok);
 	}
 
+	effect, l := l.extractEffect(desc);
+
+	one := l.copy();
+	one.pos = s.Pos();
+	one.t = IdealIntType;
+	one.evalIdealInt = func() *bignum.Integer { return bignum.Int(1) };
+
 	binop := l.copy();
 	binop.pos = s.Pos();
 	binop.doBinaryExpr(op, l, one);
@@ -673,7 +676,7 @@ func (a *stmtCompiler) doAssignOp(s *ast.AssignStmt) {
 		return;
 	}
 
-	effect, l := l.extractEffect();
+	effect, l := l.extractEffect("operator-assignment");
 
 	binop := r.copy();
 	binop.pos = s.TokPos;
@@ -822,7 +825,8 @@ func (a *stmtCompiler) DoBranchStmt(s *ast.BranchStmt) {
 		a.flow.putGoto(s.Pos(), l.name, a.block);
 
 	case token.FALLTHROUGH:
-		log.Crash("fallthrough not implemented");
+		a.diag("fallthrough outside switch");
+		return;
 
 	default:
 		log.Crash("Unexpected branch token %v", s.Tok);
@@ -910,11 +914,169 @@ func (a *stmtCompiler) DoIfStmt(s *ast.IfStmt) {
 }
 
 func (a *stmtCompiler) DoCaseClause(s *ast.CaseClause) {
-	log.Crash("Not implemented");
+	a.diag("case clause outside switch");
 }
 
 func (a *stmtCompiler) DoSwitchStmt(s *ast.SwitchStmt) {
-	log.Crash("Not implemented");
+	// Create implicit scope around switch
+	bc := a.enterChild();
+	defer bc.exit();
+
+	// Compile init statement, if any
+	if s.Init != nil {
+		bc.compileStmt(s.Init);
+	}
+
+	// Compile condition, if any, and extract its effects
+	var cond *exprCompiler;
+	condbc := bc.enterChild();
+	bad := false;
+	if s.Tag != nil {
+		e := condbc.compileExpr(condbc.block, s.Tag, false);
+		if e == nil {
+			bad = true;
+		} else {
+			var effect func(f *Frame);
+			effect, cond = e.extractEffect("switch");
+			if effect == nil {
+				bad = true;
+			}
+			a.push(func(v *vm) { effect(v.f) });
+		}
+	}
+
+	// Count cases
+	ncases := 0;
+	hasDefault := false;
+	for i, c := range s.Body.List {
+		clause, ok := c.(*ast.CaseClause);
+		if !ok {
+			a.diagAt(clause, "switch statement must contain case clauses");
+			bad = true;
+			continue;
+		}
+		if clause.Values == nil {
+			if hasDefault {
+				a.diagAt(clause, "switch statement contains more than one default case");
+				bad = true;
+			}
+			hasDefault = true;
+		} else {
+			ncases += len(clause.Values);
+		}
+	}
+
+	// Compile case expressions
+	cases := make([]func(f *Frame) bool, ncases);
+	i := 0;
+	for _, c := range s.Body.List {
+		clause, ok := c.(*ast.CaseClause);
+		if !ok {
+			continue;
+		}
+		for _, v := range clause.Values {
+			e := condbc.compileExpr(condbc.block, v, false);
+			switch {
+			case e == nil:
+				bad = true;
+			case cond == nil && !e.t.isBoolean():
+				a.diagAt(v, "'case' condition must be boolean");
+				bad = true;
+			case cond == nil:
+				cases[i] = e.asBool();
+			case cond != nil:
+				// Create comparison
+				compare := e.copy();
+				// TOOD(austin) This produces bad error messages
+				compare.doBinaryExpr(token.EQL, cond, e);
+				if compare.t == nil {
+					bad = true;
+				} else {
+					cases[i] = compare.asBool();
+				}
+			}
+			i++;
+		}
+	}
+
+	// Emit condition
+	casePCs := make([]*uint, ncases+1);
+	endPC := badPC;
+
+	if !bad {
+		a.flow.put(false, false, casePCs);
+		a.push(func(v *vm) {
+			for i, c := range cases {
+				if c(v.f) {
+					v.pc = *casePCs[i];
+					return;
+				}
+			}
+			v.pc = *casePCs[ncases];
+		});
+	}
+	condbc.exit();
+
+	// Compile cases
+	i = 0;
+	for _, c := range s.Body.List {
+		clause, ok := c.(*ast.CaseClause);
+		if !ok {
+			continue;
+		}
+
+		// Save jump PC's
+		pc := a.nextPC();
+		if clause.Values != nil {
+			for _, v := range clause.Values {
+				casePCs[i] = &pc;
+				i++;
+			}
+		} else {
+			// Default clause
+			casePCs[ncases] = &pc;
+		}
+
+		// Compile body
+		fall := false;
+		for j, s := range clause.Body {
+			if br, ok := s.(*ast.BranchStmt); ok && br.Tok == token.FALLTHROUGH {
+				println("Found fallthrough");
+				// It may be used only as the final
+				// non-empty statement in a case or
+				// default clause in an expression
+				// "switch" statement.
+				for _, s2 := range clause.Body[j+1:len(clause.Body)] {
+					// XXX(Spec) 6g also considers
+					// empty blocks to be empty
+					// statements.
+					if _, ok := s2.(*ast.EmptyStmt); !ok {
+						a.diagAt(s, "fallthrough statement must be final statement in case");
+						bad = true;
+						break;
+					}
+				}
+				fall = true;
+			} else {
+				bc.compileStmt(s);
+			}
+		}
+		// Jump out of switch, unless there was a fallthrough
+		if !fall {
+			a.flow.put1(false, &endPC);
+			a.push(func(v *vm) { v.pc = endPC });
+		}
+	}
+
+	// Get end PC
+	endPC = a.nextPC();
+	if !hasDefault {
+		casePCs[ncases] = &endPC;
+	}
+
+	if !bad {
+		a.err = false;
+	}
 }
 
 func (a *stmtCompiler) DoTypeCaseClause(s *ast.TypeCaseClause) {