Allow defining Labels as destinations for Jumps

Those Labels can be linked to a code location further ahead.

Change-Id: I82f1a719654162db0e0abb46df602ee2e01154da
Reviewed-by: Erik Verbruggen <erik.verbruggen@qt.io>
Reviewed-by: Lars Knoll <lars.knoll@qt.io>

2 files changed, 25 insertions, 8 deletions

diff --git a/src/qml/compiler/qv4bytecodegenerator.cpp b/src/qml/compiler/qv4bytecodegenerator.cpp
index 444d8385d4..6ccdeef777 100644
--- a/src/qml/compiler/qv4bytecodegenerator.cpp
+++ b/src/qml/compiler/qv4bytecodegenerator.cpp
@@ -72,13 +72,15 @@ QByteArray BytecodeGenerator::finalize()
     // resolve jumps
 //    qDebug() << "resolving jumps";
     for (const auto &j : jumps) {
-        Q_ASSERT(j.linkedInstruction != -1);
+        Q_ASSERT(j.linkedLabel != -1);
+        int linkedInstruction = labels.at(j.linkedLabel);
+        Q_ASSERT(linkedInstruction != -1);
         int offset = instructionOffsets.at(j.instructionIndex) + j.offset;
 //        qDebug() << "offset data is at" << offset;
         char *c = code.data() + offset;
-        ptrdiff_t linkedInstruction = instructionOffsets.at(j.linkedInstruction) - offset;
-//        qDebug() << "linked instruction" << j.linkedInstruction << "at " << instructionOffsets.at(j.linkedInstruction);
-        memcpy(c, &linkedInstruction, sizeof(ptrdiff_t));
+        ptrdiff_t linkedInstructionOffset = instructionOffsets.at(linkedInstruction) - offset;
+//        qDebug() << "linked instruction" << linkedInstruction << "at " << instructionOffsets.at(linkedInstruction);
+        memcpy(c, &linkedInstructionOffset, sizeof(ptrdiff_t));
     }
 
     return code;
diff --git a/src/qml/compiler/qv4bytecodegenerator_p.h b/src/qml/compiler/qv4bytecodegenerator_p.h
index 384fb22aa3..383b27e8d1 100644
--- a/src/qml/compiler/qv4bytecodegenerator_p.h
+++ b/src/qml/compiler/qv4bytecodegenerator_p.h
@@ -56,7 +56,13 @@ public:
         : function(function) {}
 
     struct Label {
+        BytecodeGenerator *generator;
         int index;
+
+        void link() {
+            Q_ASSERT(generator->labels[index] == -1);
+            generator->labels[index] = generator->instructions.size();
+        }
     };
 
     struct Jump {
@@ -74,13 +80,21 @@ public:
             link(generator->label());
         }
         void link(Label l) {
-            Q_ASSERT(generator->jumps[index].linkedInstruction == -1);
-            generator->jumps[index].linkedInstruction = l.index;
+            Q_ASSERT(generator->jumps[index].linkedLabel == -1);
+            generator->jumps[index].linkedLabel = l.index;
         }
     };
 
     Label label() {
-        return { instructions.size() };
+        Label l = { this, labels.size() };
+        labels.append(instructions.size());
+        return l;
+    }
+
+    Label newLabel() {
+        Label l = { this, labels.size() };
+        labels.append(-1);
+        return l;
     }
 
     template<int InstrT>
@@ -145,7 +159,7 @@ private:
     struct JumpData {
         int instructionIndex;
         int offset;
-        int linkedInstruction = -1;
+        int linkedLabel = -1;
     };
 
     struct I {
@@ -154,6 +168,7 @@ private:
     };
 
     QVector<I> instructions;
+    QVector<int> labels;
     QVector<JumpData> jumps;
     IR::Function *function; // ### remove me at some point
 };