V4: clarify current vs. next instruction offset in ByteCodeHandler

When executing an interpreter instruction, the code pointer points to
the next instruction. However, sometimes a pointer to the current
instruction is needed. That was hacked-around by having startInstruction
be called before updating the pointer. This is confusing and leads to
unexpected off-by-one-instruction cases.

So now during startInstruction calls and generate_instructionName calls,
there is a currentInstructionOffset() and a nextInstructionOffset() that
do what's on the tin in both places.

Change-Id: Ie8dd35ff0a7d236f008030ef4c29ec3f31c07349
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>

1 files changed, 4 insertions, 2 deletions

diff --git a/src/qml/compiler/qv4bytecodehandler_p.h b/src/qml/compiler/qv4bytecodehandler_p.h
index 5f1121306f..ca6abf3dc3 100644
--- a/src/qml/compiler/qv4bytecodehandler_p.h
+++ b/src/qml/compiler/qv4bytecodehandler_p.h
@@ -91,7 +91,8 @@ public:
 
     void decode(const char *code, uint len);
 
-    int instructionOffset() const { return _offset; }
+    int currentInstructionOffset() const { return _currentOffset; }
+    int nextInstructionOffset() const { return _nextOffset; }
 
     static std::vector<int> collectLabelsInBytecode(const char *code, uint len);
 
@@ -102,7 +103,8 @@ protected:
     virtual void endInstruction(Moth::Instr::Type instr) = 0;
 
 private:
-    int _offset = 0;
+    int _currentOffset = 0;
+    int _nextOffset = 0;
 };
 
 } // Moth namespace