From 651ea5376c57c061ebe183375974e7333d2e0ec3 Mon Sep 17 00:00:00 2001
From: Evan Cheng <evan.cheng@apple.com>
Date: Wed, 2 Dec 2009 22:02:52 +0000
Subject: Skeleton for MachineInstr level SSA updater.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@90353 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/CodeGen/MachineSSAUpdater.cpp | 108 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 108 insertions(+)
 create mode 100644 lib/CodeGen/MachineSSAUpdater.cpp

(limited to 'lib/CodeGen/MachineSSAUpdater.cpp')

diff --git a/lib/CodeGen/MachineSSAUpdater.cpp b/lib/CodeGen/MachineSSAUpdater.cpp
new file mode 100644
index 0000000000..c0eb170cfb
--- /dev/null
+++ b/lib/CodeGen/MachineSSAUpdater.cpp
@@ -0,0 +1,108 @@
+//===- MachineSSAUpdater.cpp - Unstructured SSA Update Tool ---------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements the MachineSSAUpdater class.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/CodeGen/MachineSSAUpdater.h"
+#include "llvm/CodeGen/MachineInstr.h"
+#include "llvm/ADT/DenseMap.h"
+using namespace llvm;
+
+typedef DenseMap<MachineBasicBlock*, unsigned > AvailableValsTy;
+typedef std::vector<std::pair<MachineBasicBlock*, unsigned> >
+                IncomingPredInfoTy;
+
+static AvailableValsTy &getAvailableVals(void *AV) {
+  return *static_cast<AvailableValsTy*>(AV);
+}
+
+static IncomingPredInfoTy &getIncomingPredInfo(void *IPI) {
+  return *static_cast<IncomingPredInfoTy*>(IPI);
+}
+
+
+MachineSSAUpdater::MachineSSAUpdater(SmallVectorImpl<MachineInstr*> *NewPHI)
+  : AV(0), IPI(0), InsertedPHIs(NewPHI) {}
+
+MachineSSAUpdater::~MachineSSAUpdater() {
+  delete &getAvailableVals(AV);
+  delete &getIncomingPredInfo(IPI);
+}
+
+/// Initialize - Reset this object to get ready for a new set of SSA
+/// updates.  ProtoValue is the value used to name PHI nodes.
+void MachineSSAUpdater::Initialize() {
+  if (AV == 0)
+    AV = new AvailableValsTy();
+  else
+    getAvailableVals(AV).clear();
+
+  if (IPI == 0)
+    IPI = new IncomingPredInfoTy();
+  else
+    getIncomingPredInfo(IPI).clear();
+}
+
+/// HasValueForBlock - Return true if the MachineSSAUpdater already has a value for
+/// the specified block.
+bool MachineSSAUpdater::HasValueForBlock(MachineBasicBlock *BB) const {
+  return getAvailableVals(AV).count(BB);
+}
+
+/// AddAvailableValue - Indicate that a rewritten value is available in the
+/// specified block with the specified value.
+void MachineSSAUpdater::AddAvailableValue(MachineBasicBlock *BB, unsigned V) {
+  getAvailableVals(AV)[BB] = V;
+}
+
+/// GetValueAtEndOfBlock - Construct SSA form, materializing a value that is
+/// live at the end of the specified block.
+unsigned MachineSSAUpdater::GetValueAtEndOfBlock(MachineBasicBlock *BB) {
+  return GetValueAtEndOfBlockInternal(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 MachineSSAUpdater::GetValueInMiddleOfBlock(MachineBasicBlock *BB) {
+  return 0;
+}
+
+/// RewriteUse - Rewrite a use of the symbolic value.  This handles PHI nodes,
+/// which use their value in the corresponding predecessor.
+void MachineSSAUpdater::RewriteUse(unsigned &U) {
+}
+
+
+/// GetValueAtEndOfBlockInternal - Check to see if AvailableVals has an entry
+/// for the specified BB and if so, return it.  If not, construct SSA form by
+/// walking predecessors inserting PHI nodes as needed until we get to a block
+/// where the value is available.
+///
+unsigned MachineSSAUpdater::GetValueAtEndOfBlockInternal(MachineBasicBlock *BB){
+  return 0;
+}
-- 
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