add the start of a class used to handle phi translation in memdep and

gvn (this is just a skeleton so far).  This will ultimately be used
to fix a nasty miscompilation with GVN.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@90518 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/Analysis/PHITransAddr.h

@@ -0,0 +1,91 @@
+//===- PHITransAddr.h - PHI Translation for Addresses -----------*- 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 PHITransAddr class.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_ANALYSIS_PHITRANSADDR_H
+#define LLVM_ANALYSIS_PHITRANSADDR_H
+
+#include "llvm/Instruction.h"
+#include "llvm/ADT/SmallVector.h"
+
+namespace llvm {
+  class DominatorTree;
+  class TargetData;
+  
+/// PHITransAddr - An address value which tracks and handles phi translation.
+/// As we walk "up" the CFG through predecessors, we need to ensure that the
+/// address we're tracking is kept up to date.  For example, if we're analyzing
+/// an address of "&A[i]" and walk through the definition of 'i' which is a PHI
+/// node, we *must* phi translate i to get "&A[j]" or else we will analyze an
+/// incorrect pointer in the predecessor block.
+///
+/// This is designed to be a relatively small object that lives on the stack and
+/// is copyable.
+///
+class PHITransAddr {
+  /// Addr - The actual address we're analyzing.
+  Value *Addr;
+  
+  /// InstInputs - The inputs for our symbolic address.
+  SmallVector<Instruction*, 4> InstInputs;
+public:
+  PHITransAddr(Value *addr) : Addr(addr) {
+    // If the address is an instruction, the whole thing is considered an input.
+    if (Instruction *I = dyn_cast<Instruction>(Addr))
+      InstInputs.push_back(I);
+  }
+  
+  /// NeedsPHITranslationFromBlock - Return true if moving from the specified
+  /// BasicBlock to its predecessors requires PHI translation.
+  bool NeedsPHITranslationFromBlock(BasicBlock *BB) const {
+    // We do need translation if one of our input instructions is defined in
+    // this block.
+    for (unsigned i = 0, e = InstInputs.size(); i != e; ++i)
+      if (InstInputs[i]->getParent() == BB)
+        return true;
+    return false;
+  }
+  
+  /// IsPHITranslatable - If this needs PHI translation, return true if we have
+  /// some hope of doing it.  This should be used as a filter to avoid calling
+  /// GetPHITranslatedValue in hopeless situations.
+  bool IsPHITranslatable() const;
+  
+  /// GetPHITranslatedValue - Given a computation that satisfied the
+  /// isPHITranslatable predicate, see if we can translate the computation into
+  /// the specified predecessor block.  If so, return that value, otherwise
+  /// return null.
+  Value *GetPHITranslatedValue(Value *InVal, BasicBlock *CurBB,
+                               BasicBlock *Pred, const TargetData *TD) const;
+  
+  /// GetAvailablePHITranslatePointer - Return the value computed by
+  /// PHITranslatePointer if it dominates PredBB, otherwise return null.
+  Value *GetAvailablePHITranslatedValue(Value *V,
+                                        BasicBlock *CurBB, BasicBlock *PredBB,
+                                        const TargetData *TD,
+                                        const DominatorTree &DT) const;
+  
+  /// InsertPHITranslatedPointer - Insert a computation of the PHI translated
+  /// version of 'V' for the edge PredBB->CurBB into the end of the PredBB
+  /// block.  All newly created instructions are added to the NewInsts list.
+  /// This returns null on failure.
+  ///
+  Value *InsertPHITranslatedPointer(Value *InVal, BasicBlock *CurBB,
+                                    BasicBlock *PredBB, const TargetData *TD,
+                                    const DominatorTree &DT,
+                                 SmallVectorImpl<Instruction*> &NewInsts) const;
+    
+};
+
+} // end namespace llvm
+
+#endif

lib/Analysis/PHITransAddr.cpp

@@ -0,0 +1,71 @@
+//===- PHITransAddr.cpp - PHI Translation for Addresses -------------------===//
+//
+//                     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 PHITransAddr class.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Analysis/PHITransAddr.h"
+#include "llvm/Analysis/Dominators.h"
+using namespace llvm;
+
+/// IsPHITranslatable - If this needs PHI translation, return true if we have
+/// some hope of doing it.  This should be used as a filter to avoid calling
+/// GetPHITranslatedValue in hopeless situations.
+bool PHITransAddr::IsPHITranslatable() const {
+  return true; // not a good filter.
+}
+
+/// GetPHITranslatedValue - Given a computation that satisfied the
+/// isPHITranslatable predicate, see if we can translate the computation into
+/// the specified predecessor block.  If so, return that value, otherwise
+/// return null.
+Value *PHITransAddr::GetPHITranslatedValue(Value *InVal, BasicBlock *CurBB,
+                                           BasicBlock *Pred,
+                                           const TargetData *TD) const {
+  // Not a great implementation.
+  return 0;
+}
+
+/// GetAvailablePHITranslatePointer - Return the value computed by
+/// PHITranslatePointer if it dominates PredBB, otherwise return null.
+Value *PHITransAddr::
+GetAvailablePHITranslatedValue(Value *V,
+                               BasicBlock *CurBB, BasicBlock *PredBB,
+                               const TargetData *TD,
+                               const DominatorTree &DT) const {
+  // See if PHI translation succeeds.
+  V = GetPHITranslatedValue(V, CurBB, PredBB, TD);
+  if (V == 0) return 0;
+  
+  // Make sure the value is live in the predecessor.
+  if (Instruction *Inst = dyn_cast_or_null<Instruction>(V))
+    if (!DT.dominates(Inst->getParent(), PredBB))
+      return 0;
+  return V;
+}
+
+/// InsertPHITranslatedPointer - Insert a computation of the PHI translated
+/// version of 'V' for the edge PredBB->CurBB into the end of the PredBB
+/// block.  All newly created instructions are added to the NewInsts list.
+/// This returns null on failure.
+///
+Value *PHITransAddr::
+InsertPHITranslatedPointer(Value *InVal, BasicBlock *CurBB,
+                           BasicBlock *PredBB, const TargetData *TD,
+                           const DominatorTree &DT,
+                           SmallVectorImpl<Instruction*> &NewInsts) const {
+  // See if we have a version of this value already available and dominating
+  // PredBB.  If so, there is no need to insert a new copy.
+  if (Value *Res = GetAvailablePHITranslatedValue(InVal, CurBB, PredBB, TD, DT))
+    return Res;
+
+  // Not a great implementation.
+  return 0;
+}