Fix constant folding for simple binary expression

This change improves constant folding of numeric and
string literals.

Also, we go back generating quadruples instead of
IR-tree-expressions. This is kind of needed to reduce register
pressure in the V4 VM. That is, V4 has typed registers so before
reusing a register we need to look at the type and eventually
dispose its contents (e.g. when a QString or a QUrl is stored
in the register). Unfortunately, we can't effort to have all
these checks in the V4 instructions. So we change `binop'
to generate literals (e.g. CONST or STRING) or a TEMP (aka
a preassigned register that cannot be reused).

For exmaple, the IR code generated for

  Rectangle {
    color: "b" + "l" + ("u" + "e")
    width: 10 + 20 + 30
  }

is

====================
	line: 3	column: 10
L0x811ca10:
	t0 = string_to_color("blue");
	return t0;

====================
	line: 4	column: 10
L0x811ca50:
	return 60;

Change-Id: I4d8482ddab9193d8469bda6461bfb2e5a3eeb197
Reviewed-by: Aaron Kennedy <aaron.kennedy@nokia.com>

1 files changed, 8 insertions, 1 deletions

diff --git a/src/qml/qml/v4/qv4irbuilder.cpp b/src/qml/qml/v4/qv4irbuilder.cpp
index b8210b863f..31ed9a5a6a 100644
--- a/src/qml/qml/v4/qv4irbuilder.cpp
+++ b/src/qml/qml/v4/qv4irbuilder.cpp
@@ -892,7 +892,14 @@ void QV4IRBuilder::binop(AST::BinaryExpression *ast, ExprResult left, ExprResult
         _expr.format = ExprResult::cx;
         _block->CJUMP(_block->BINOP(IR::binaryOperator(ast->op), left, right), _expr.iftrue, _expr.iffalse);
     } else {
-        _expr.code = _block->BINOP(IR::binaryOperator(ast->op), left, right);
+        IR::Expr *e = _block->BINOP(IR::binaryOperator(ast->op), left, right);
+        if (e->asConst() != 0 || e->asString() != 0)
+            _expr.code = e;
+        else {
+            IR::Temp *t = _block->TEMP(e->type);
+            _block->MOVE(t, e);
+            _expr.code = t;
+        }
     }
 }