Skeleton for MachineInstr level SSA updater.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@90353 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 99 insertions, 0 deletions

diff --git a/include/llvm/CodeGen/MachineSSAUpdater.h b/include/llvm/CodeGen/MachineSSAUpdater.h
new file mode 100644
index 0000000000..a785ab8cfa
--- /dev/null
+++ b/include/llvm/CodeGen/MachineSSAUpdater.h
@@ -0,0 +1,99 @@
+//===-- MachineSSAUpdater.h - Unstructured SSA Update Tool ------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file declares the MachineSSAUpdater class.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CODEGEN_MACHINESSAUPDATER_H
+#define LLVM_CODEGEN_MACHINESSAUPDATER_H
+
+namespace llvm {
+  class MachineBasicBlock;
+  class MachineInstr;
+  template<typename T> class SmallVectorImpl;
+
+/// SSAUpdater - This class updates SSA form for a set of values defined in
+/// multiple blocks.  This is used when code duplication or another unstructured
+/// transformation wants to rewrite a set of uses of one value with uses of a
+/// set of values.
+class MachineSSAUpdater {
+  /// AvailableVals - This keeps track of which value to use on a per-block
+  /// basis.  When we insert PHI nodes, we keep track of them here.
+  //typedef DenseMap<MachineBasicBlock*, unsigned > AvailableValsTy;
+  void *AV;
+
+  /// IncomingPredInfo - We use this as scratch space when doing our recursive
+  /// walk.  This should only be used in GetValueInBlockInternal, normally it
+  /// should be empty.
+  //std::vector<std::pair<MachineBasicBlock*, unsigned > > IncomingPredInfo;
+  void *IPI;
+
+  /// InsertedPHIs - If this is non-null, the MachineSSAUpdater adds all PHI
+  /// nodes that it creates to the vector.
+  SmallVectorImpl<MachineInstr*> *InsertedPHIs;
+public:
+  /// MachineSSAUpdater constructor.  If InsertedPHIs is specified, it will be
+  /// filled in with all PHI Nodes created by rewriting.
+  explicit MachineSSAUpdater(SmallVectorImpl<MachineInstr*> *InsertedPHIs = 0);
+  ~MachineSSAUpdater();
+
+  /// Initialize - Reset this object to get ready for a new set of SSA
+  /// updates.
+  void Initialize();
+
+  /// AddAvailableValue - Indicate that a rewritten value is available at the
+  /// end of the specified block with the specified value.
+  void AddAvailableValue(MachineBasicBlock *BB, unsigned V);
+
+  /// HasValueForBlock - Return true if the MachineSSAUpdater already has a
+  /// value for the specified block.
+  bool HasValueForBlock(MachineBasicBlock *BB) const;
+
+  /// GetValueAtEndOfBlock - Construct SSA form, materializing a value that is
+  /// live at the end of the specified block.
+  unsigned GetValueAtEndOfBlock(MachineBasicBlock *BB);
+
+  /// GetValueInMiddleOfBlock - Construct SSA form, materializing a value that
+  /// is live in the middle of the specified block.
+  ///
+  /// GetValueInMiddleOfBlock is the same as GetValueAtEndOfBlock except in one
+  /// important case: if there is a definition of the rewritten value after the
+  /// 'use' in BB.  Consider code like this:
+  ///
+  ///      X1 = ...
+  ///   SomeBB:
+  ///      use(X)
+  ///      X2 = ...
+  ///      br Cond, SomeBB, OutBB
+  ///
+  /// In this case, there are two values (X1 and X2) added to the AvailableVals
+  /// set by the client of the rewriter, and those values are both live out of
+  /// their respective blocks.  However, the use of X happens in the *middle* of
+  /// a block.  Because of this, we need to insert a new PHI node in SomeBB to
+  /// merge the appropriate values, and this value isn't live out of the block.
+  ///
+  unsigned GetValueInMiddleOfBlock(MachineBasicBlock *BB);
+
+  /// RewriteUse - Rewrite a use of the symbolic value.  This handles PHI nodes,
+  /// which use their value in the corresponding predecessor.  Note that this
+  /// will not work if the use is supposed to be rewritten to a value defined in
+  /// the same block as the use, but above it.  Any 'AddAvailableValue's added
+  /// for the use's block will be considered to be below it.
+  void RewriteUse(unsigned &U);
+
+private:
+  unsigned GetValueAtEndOfBlockInternal(MachineBasicBlock *BB);
+  void operator=(const MachineSSAUpdater&); // DO NOT IMPLEMENT
+  MachineSSAUpdater(const MachineSSAUpdater&);     // DO NOT IMPLEMENT
+};
+
+} // End llvm namespace
+
+#endif