1 files changed, 94 insertions, 0 deletions
diff --git a/Source/JavaScriptCore/dfg/DFGSSAConversionPhase.h b/Source/JavaScriptCore/dfg/DFGSSAConversionPhase.h
new file mode 100644
index 000000000..027f8156f
--- /dev/null
+++ b/Source/JavaScriptCore/dfg/DFGSSAConversionPhase.h
@@ -0,0 +1,94 @@
+/*
+ * Copyright (C) 2013, 2014 Apple Inc. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
+ * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+ * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE INC. OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
+ * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+ * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
+ * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
+ * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 
+ */
+
+#ifndef DFGSSAConversionPhase_h
+#define DFGSSAConversionPhase_h
+
+#if ENABLE(DFG_JIT)
+
+namespace JSC { namespace DFG {
+
+class Graph;
+
+// Convert ThreadedCPS form into SSA form. This results in a form that has:
+//
+// - Minimal Phi's. We use the the Cytron et al (TOPLAS'91) algorithm for
+//   Phi insertion. Most of the algorithm is implemented in SSACalculator
+//   and Dominators.
+//
+// - No uses of GetLocal/SetLocal except for captured variables and flushes.
+//   After this, any remaining SetLocal means Flush. PhantomLocals become
+//   Phantoms. Nodes may have children that are in another basic block.
+//
+// - MovHints are used for OSR information, and are themselves minimal.
+//   A MovHint will occur at some point after the assigning, and at Phi
+//   points.
+//
+// - Unlike conventional SSA in which Phi functions refer to predecessors
+//   and values, our SSA uses Upsilon functions to indicate values in
+//   predecessors. A merge will look like:
+//
+//   labelA:
+//       a: Thingy(...)
+//       b: Upsilon(^e, @a)
+//       Jump(labelC)
+//
+//   labelB:
+//       c: OtherThingy(...)
+//       d: Upsilon(^e, @c)
+//       Jump(labelC)
+//
+//   labelC:
+//       e: Phi()
+//
+//   Note that the Phi has no children, but the predecessors have Upsilons
+//   that have a weak reference to the Phi (^e instead of @e; we store it
+//   in the OpInfo rather than the AdjacencyList). Think of the Upsilon
+//   as "assigning" to the "variable" associated with the Phi, and that
+//   this is the one place in SSA form where you can have multiple
+//   assignments.
+//
+//   This implies some other loosenings of SSA. For example, an Upsilon
+//   may precede a Phi in the same basic block; this may arise after CFG
+//   simplification. Although it's profitable for CFG simplification (or
+//   some other phase) to remove these, it's not strictly necessary. As
+//   well, this form allows the Upsilon to be in any block that dominates
+//   the predecessor block of the Phi, which allows for block splitting to
+//   ignore the possibility of introducing an extra edge between the Phi
+//   and the predecessor (though normal SSA would allow this, also, with
+//   the caveat that the Phi predecessor block lists would have to be
+//   updated).
+//
+//   Fun fact: Upsilon is so named because it comes before Phi in the
+//   alphabet. It can be written as "Y".
+
+bool performSSAConversion(Graph&);
+
+} } // namespace JSC::DFG
+
+#endif // ENABLE(DFG_JIT)
+
+#endif // DFGSSAConversionPhase_h
+