V4: Generate labels for backward jumps

When analyzing the bytecode from top-to-bottom in a single pass, we
don't know when a jump back to previously seen code occurs. For example,
in the baseline JIT we would already have generated code for some
bytecode when we see a jump back (like at the end of a loop body), and
we can't go back and insert a label to jump to.

As JavaScript has no goto's, the only backward jumps are at the end of
loops, so there are very few cases where we need to actually generate
labels.

This was previously handled by analyzing the bytecode twice: once to
collect all jump targets, and then second pass over the bytecode to do
the actual JITting (which would use the jump targets to insert labels).
We can now do that with one single pass. So the trade-off is to store
4 bytes more per function plus 4 bytes for each loop, instead of having
to analyze all functions only to find where all jumps are each time that
function is JITted.

Change-Id: I3abfcb69f65851a397dbd4a9762ea5e9e57495f6
Reviewed-by: Ulf Hermann <ulf.hermann@qt.io>

1 files changed, 11 insertions, 4 deletions

diff --git a/src/qml/compiler/qv4compileddata_p.h b/src/qml/compiler/qv4compileddata_p.h
index 52c8e9f651..7197b4cde8 100644
--- a/src/qml/compiler/qv4compileddata_p.h
+++ b/src/qml/compiler/qv4compileddata_p.h
@@ -73,7 +73,7 @@
 QT_BEGIN_NAMESPACE
 
 // Bump this whenever the compiler data structures change in an incompatible way.
-#define QV4_DATA_STRUCTURE_VERSION 0x1a
+#define QV4_DATA_STRUCTURE_VERSION 0x1b
 
 class QIODevice;
 class QQmlPropertyCache;
@@ -302,9 +302,14 @@ struct Function
     typedef quint16_le TraceInfoCount;
     TraceInfoCount nTraceInfos;
     static constexpr TraceInfoCount NoTracing() { return TraceInfoCount::max(); }
+
+    quint32_le nLabelInfos;
+    size_t labelInfosOffset() const { return dependingScopePropertiesOffset() + nDependingScopeProperties; }
+
     // Keep all unaligned data at the end
     quint8 flags;
     quint8 padding1;
+    quint16 padding2;
 
     //    quint32 formalsIndex[nFormals]
     //    quint32 localsIndex[nLocals]
@@ -321,12 +326,14 @@ struct Function
     const quint32_le *formalsEnd() const { return formalsTable() + nFormals; }
     // ---
 
+    const quint32_le *labelInfoTable() const { return reinterpret_cast<const quint32_le *>(reinterpret_cast<const char *>(this) + labelInfosOffset()); }
+
     const char *code() const { return reinterpret_cast<const char *>(this) + codeOffset; }
 
     inline bool hasQmlDependencies() const { return nDependingIdObjects > 0 || nDependingContextProperties > 0 || nDependingScopeProperties > 0; }
 
-    static int calculateSize(int nFormals, int nLocals, int nLines, int nInnerfunctions, int nIdObjectDependencies, int nPropertyDependencies, int codeSize) {
-        int trailingData = (nFormals + nLocals + nInnerfunctions +  nIdObjectDependencies +
+    static int calculateSize(int nFormals, int nLocals, int nLines, int nInnerfunctions, int nIdObjectDependencies, int nPropertyDependencies, int labelInfoSize, int codeSize) {
+        int trailingData = (nFormals + nLocals + nInnerfunctions +  nIdObjectDependencies + labelInfoSize +
                 2 * nPropertyDependencies)*sizeof (quint32) + nLines*sizeof(CodeOffsetToLine);
         size_t size = align(align(sizeof(Function)) + size_t(trailingData)) + align(codeSize);
         Q_ASSERT(size < INT_MAX);
@@ -337,7 +344,7 @@ struct Function
         return (a + 7) & ~size_t(7);
     }
 };
-static_assert(sizeof(Function) == 56, "Function structure needs to have the expected size to be binary compatible on disk when generated by host compiler and loaded by target");
+static_assert(sizeof(Function) == 60, "Function structure needs to have the expected size to be binary compatible on disk when generated by host compiler and loaded by target");
 
 struct Method {
     enum Type {