Subzero: Control whether deleted instructions are retained.

src/IceCfg.h

Index: src/IceCfg.h
diff --git a/src/IceCfg.h b/src/IceCfg.h
index d3aabe93915ef29435bd761e4d876beab91145de..88178fd1b5c0a17fb0b11f6d38b3d0de4224fb37 100644
--- a/src/IceCfg.h
+++ b/src/IceCfg.h
@@ -185,6 +185,14 @@ public:
   /// predecessor and successor edges, in the form of CfgNode::InEdges[] and
   /// CfgNode::OutEdges[].
   void computeInOutEdges();
+  /// Renumber the non-deleted instructions in the Cfg.  This needs to be done
+  /// in preparation for live range analysis.  The instruction numbers in a
+  /// block must be monotonically increasing.  The range of instruction numbers
+  /// in a block, from lowest to highest, must not overlap with the range of any
+  /// other block.
+  ///
+  /// Also, if the configuration specifies to do so, remove/unlink all deleted
+  /// instructions from the Cfg, to speed up later passes over the instructions.
   void renumberInstructions();
   void placePhiLoads();
   void placePhiStores();