1 files changed, 96 insertions, 0 deletions
diff --git a/src/main/java/com/seaofnodes/simple/parser/ControlFlow.java b/src/main/java/com/seaofnodes/simple/parser/ControlFlow.java
new file mode 100644
index 00000000..caa73076
--- /dev/null
+++ b/src/main/java/com/seaofnodes/simple/parser/ControlFlow.java
@@ -0,0 +1,96 @@
+package com.seaofnodes.simple.parser;
+
+import com.seaofnodes.simple.node.*;
+import com.seaofnodes.simple.parser.Parser.ParseException;
+import com.seaofnodes.simple.type.*;
+
+import static com.seaofnodes.simple.util.Utils.TODO;
+
+/** Shared guarded branch/merge construction for if, ?:, && and ||. */
+final class ControlFlow {
+    private final Parser P;
+
+    ControlFlow(Parser P) { this.P = P; }
+
+    // Parse a conditional expression, merging results.
+    Node conditional( Node pred, String fside ) {
+        // IfNode takes current control and predicate
+        pred.keep();
+        Node ifNode = new IfNode(P.ctrl(), pred).peephole();
+        // Setup projection nodes
+        CFGNode ifT = new CProjNode(ifNode.  keep(), 0, "True" ).peephole().keep();
+        CFGNode ifF = new CProjNode(ifNode.unkeep(), 1, "False").peephole().keep();
+        // In if true branch, the ifT proj node becomes the ctrl
+        // But first clone the scope and set it as current
+        ScopeNode fScope = P._scope.dup(); // Duplicate current scope
+        fScope.ctrl(ifF);       // The pending arm already starts at False
+        P._xScopes.push(fScope); // For graph visualization we need all scopes
+
+        // Parse the true side
+        P.ctrl(ifT.unkeep());     // set ctrl token to ifTrue projection
+        P._scope.addGuards(ifT,pred,false); // Up-cast predicate
+        // Parse true-side flavor
+        Node lhs = switch( fside ) {
+        case "else" -> P.statements.parseStatement(); // if( pred )  stmts;
+        case ":"    -> P.expressions.parseAssignment();      //     pred ?  asgn;
+        case "&&"   -> P.expressions.parseLogical();   //     pred && expr
+        case "||"   -> pred;             //     pred || expr_is_ignored
+        default     -> throw TODO();
+        };
+        lhs.keep();
+        P._scope.removeGuards(ifT);
+
+        // See if a one-sided def was made: "if(pred) int x = 1;" and throw.
+        // See if any forward-refs were made, and copy them to the other side:
+        // "pred ? n*fact(n-1) : 1"
+        fScope.balanceIf(P._scope);
+
+        ScopeNode tScope = P._scope;
+
+        // Parse the false side
+        P._scope = fScope;        // Restore scope, then parse else block if any
+        ifF.unkeep();           // fScope already owns the false control
+        // Up-cast predicate, even if not else clause, because predicate can
+        // remain true if the true clause exits: `if( !ptr ) return 0; return ptr.fld;`
+        P._scope.addGuards(ifF,pred,true);
+        // Parse false-side flavor
+        boolean doRHS = false;  // RHS is optional for if/else and trinary
+        Node rhs = switch( fside ) {
+        case "else" -> (doRHS = P.match(fside)) ? P.statements.parseStatement() : P.con(lhs._type.makeZero());
+        case ":"    -> (doRHS = P.match(fside)) ? P.expressions.parseAssignment()      : P.con(lhs._type.makeZero());
+        case "&&"   -> P.con(lhs._type.makeZero()); // pred && expr_is_ignored
+        case "||"   -> P.expressions.parseLogical();            // pred || expr
+        default     -> throw TODO();
+        };
+        rhs.keep();
+        P._scope.removeGuards(ifF);
+        // The RHS of `||` is parsed on the false side, so retain its updated
+        // control, memory and locals just as an explicit else arm does.
+        if( doRHS || fside.equals("||") )
+            fScope = P._scope;
+        pred.unkeep();
+
+        // Check the trinary widening int/flt
+        if( !fside.equals("else") ) {
+            rhs = P.conversions.widenInt( rhs.unkeep(), lhs._type ).keep();
+            lhs = P.conversions.widenInt( lhs.unkeep(), rhs._type ).keep();
+        }
+
+        P._scope = tScope;
+        P._xScopes.pop();       // Discard pushed from graph display
+        // See if a one-sided def was made: "if(pred) int x = 1;" and throw.
+        // See if any forward-refs were made, and copy them to the other side:
+        // "pred ? n*fact(n-1) : 1"
+        tScope.balanceIf(fScope);
+
+        // Merge results
+        RegionNode r = P.ctrl(tScope.mergeScopes(fScope,P.loc()));
+        Node ret = P.peep(new PhiNode("",r,lhs.unkeep(),rhs.unkeep()));
+        // Immediately fail e.g. `arg ? 7 : ptr`
+        ParseException err;
+        if( !fside.equals("else") && (err = ret.err()) !=null ) throw err;
+        ret.keep();
+        r.peephole();
+        return ret.unkeep();
+    }
+}