Implement an efficient and fully general SSA update mechanism that

works on unstructured CFGs.  This implements PR217, our oldest open PR.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@83705 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 71 insertions, 0 deletions

diff --git a/include/llvm/Transforms/Utils/SSAUpdater.h b/include/llvm/Transforms/Utils/SSAUpdater.h
new file mode 100644
index 0000000000..5e11984bf3
--- /dev/null
+++ b/include/llvm/Transforms/Utils/SSAUpdater.h
@@ -0,0 +1,71 @@
+//===-- SSAUpdater.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 SSAUpdater class.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_TRANSFORMS_UTILS_SSAUPDATER_H
+#define LLVM_TRANSFORMS_UTILS_SSAUPDATER_H
+
+namespace llvm {
+  class Value;
+  class BasicBlock;
+  class Use;
+  
+/// 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 SSAUpdater {
+  /// 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.  We use
+  /// WeakVH's for the value of the map because we RAUW PHI nodes when we
+  /// eliminate them, and want the WeakVH to track this.
+  //typedef DenseMap<BasicBlock*, TrackingVH<Value> > AvailableValsTy;
+  void *AV;
+  
+  /// PrototypeValue is an arbitrary representative value, which we derive names
+  /// and a type for PHI nodes.
+  Value *PrototypeValue;
+  
+  /// 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<BasicBlock*, TrackingVH<Value> > > IncomingPredInfo;
+  void *IPI;
+public:
+  SSAUpdater();
+  ~SSAUpdater();
+  
+  /// Initialize - Reset this object to get ready for a new set of SSA
+  /// updates.  ProtoValue is the value used to name PHI nodes.
+  void Initialize(Value *ProtoValue);
+  
+  /// AddAvailableValue - Indicate that a rewritten value is available in the
+  /// specified block with the specified value.
+  void AddAvailableValue(BasicBlock *BB, Value *V);
+  
+  /// GetValueInBlock - Construct SSA form, materializing a value in the
+  /// specified block.
+  Value *GetValueInBlock(BasicBlock *BB);
+  
+  /// RewriteUse - Rewrite a use of the symbolic value.  This handles PHI nodes,
+  /// which use their value in the corresponding predecessor.
+  void RewriteUse(Use &U);
+  
+private:
+  Value *GetValueInBlockInternal(BasicBlock *BB);
+  void operator=(const SSAUpdater&); // DO NOT IMPLEMENT
+  SSAUpdater(const SSAUpdater&);     // DO NOT IMPLEMENT
+};
+
+} // End llvm namespace
+
+#endif