V4: Do not invert non-reflexive comparison binops

This is only useful for the few (4) comparisons where we have
specialized instructions, and it's very error-prone.

Change-Id: I37efe94f54ba0adf393d9236df2d13aa6685eb46
Fixes: QTBUG-74476
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>

2 files changed, 46 insertions, 49 deletions

diff --git a/src/qml/compiler/qv4codegen.cpp b/src/qml/compiler/qv4codegen.cpp
index b0bec5b6f2..3fdba08f20 100644
--- a/src/qml/compiler/qv4codegen.cpp
+++ b/src/qml/compiler/qv4codegen.cpp
@@ -1738,59 +1738,46 @@ Codegen::Reference Codegen::binopHelper(QSOperator::Op oper, Reference &left, Re
     return Reference::fromAccumulator(this);
 }
 
-static QSOperator::Op operatorForSwappedOperands(QSOperator::Op oper)
-{
-    switch (oper) {
-    case QSOperator::StrictEqual: return QSOperator::StrictEqual;
-    case QSOperator::StrictNotEqual: return QSOperator::StrictNotEqual;
-    case QSOperator::Equal: return QSOperator::Equal;
-    case QSOperator::NotEqual: return QSOperator::NotEqual;
-    case QSOperator::Gt: return QSOperator::Le;
-    case QSOperator::Ge: return QSOperator::Lt;
-    case QSOperator::Lt: return QSOperator::Ge;
-    case QSOperator::Le: return QSOperator::Gt;
-    default: Q_UNIMPLEMENTED(); return QSOperator::Invalid;
-    }
-}
-
 Codegen::Reference Codegen::jumpBinop(QSOperator::Op oper, Reference &left, Reference &right)
 {
-    if (left.isConstant()) {
-        oper = operatorForSwappedOperands(oper);
-        qSwap(left, right);
-    }
+    // See if we can generate specialized comparison instructions:
+    if (oper == QSOperator::Equal || oper == QSOperator::NotEqual) {
+        // Because == and != are reflexive, we can do the following:
+        if (left.isConstant() && !right.isConstant())
+            qSwap(left, right); // null==a -> a==null
 
-    if (right.isConstant() && (oper == QSOperator::Equal || oper == QSOperator::NotEqual)) {
-        Value c = Value::fromReturnedValue(right.constant);
-        if (c.isNull() || c.isUndefined()) {
-            left.loadInAccumulator();
-            if (oper == QSOperator::Equal) {
-                Instruction::CmpEqNull cmp;
-                bytecodeGenerator->addInstruction(cmp);
-                addCJump();
-                return Reference();
-            } else if (oper == QSOperator::NotEqual) {
-                Instruction::CmpNeNull cmp;
-                bytecodeGenerator->addInstruction(cmp);
-                addCJump();
-                return Reference();
-            }
-        } else if (c.isInt32()) {
-            left.loadInAccumulator();
-            if (oper == QSOperator::Equal) {
-                Instruction::CmpEqInt cmp;
-                cmp.lhs = c.int_32();
-                bytecodeGenerator->addInstruction(cmp);
-                addCJump();
-                return Reference();
-            } else if (oper == QSOperator::NotEqual) {
-                Instruction::CmpNeInt cmp;
-                cmp.lhs = c.int_32();
-                bytecodeGenerator->addInstruction(cmp);
-                addCJump();
-                return Reference();
-            }
+        if (right.isConstant()) {
+            Value c = Value::fromReturnedValue(right.constant);
+            if (c.isNull() || c.isUndefined()) {
+                left.loadInAccumulator();
+                if (oper == QSOperator::Equal) {
+                    Instruction::CmpEqNull cmp;
+                    bytecodeGenerator->addInstruction(cmp);
+                    addCJump();
+                    return Reference();
+                } else if (oper == QSOperator::NotEqual) {
+                    Instruction::CmpNeNull cmp;
+                    bytecodeGenerator->addInstruction(cmp);
+                    addCJump();
+                    return Reference();
+                }
+            } else if (c.isInt32()) {
+                left.loadInAccumulator();
+                if (oper == QSOperator::Equal) {
+                    Instruction::CmpEqInt cmp;
+                    cmp.lhs = c.int_32();
+                    bytecodeGenerator->addInstruction(cmp);
+                    addCJump();
+                    return Reference();
+                } else if (oper == QSOperator::NotEqual) {
+                    Instruction::CmpNeInt cmp;
+                    cmp.lhs = c.int_32();
+                    bytecodeGenerator->addInstruction(cmp);
+                    addCJump();
+                    return Reference();
+                }
 
+            }
         }
     }
 
diff --git a/tests/auto/qml/qjsengine/tst_qjsengine.cpp b/tests/auto/qml/qjsengine/tst_qjsengine.cpp
index 42d8f37ca8..0491ccd473 100644
--- a/tests/auto/qml/qjsengine/tst_qjsengine.cpp
+++ b/tests/auto/qml/qjsengine/tst_qjsengine.cpp
@@ -235,6 +235,8 @@ private slots:
     void importModuleWithLexicallyScopedVars();
     void importExportErrors();
 
+    void equality();
+
 public:
     Q_INVOKABLE QJSValue throwingCppMethod1();
     Q_INVOKABLE void throwingCppMethod2();
@@ -4622,6 +4624,14 @@ void tst_QJSEngine::importExportErrors()
     }
 }
 
+void tst_QJSEngine::equality()
+{
+    QJSEngine engine;
+    QJSValue ok = engine.evaluate("(0 < 0) ? 'ko' : 'ok'");
+    QVERIFY(ok.isString());
+    QCOMPARE(ok.toString(), QString("ok"));
+}
+
 QTEST_MAIN(tst_QJSEngine)
 
 #include "tst_qjsengine.moc"