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

1 files changed, 71 insertions, 0 deletions

diff --git a/lib/Analysis/PHITransAddr.cpp b/lib/Analysis/PHITransAddr.cpp
new file mode 100644
index 0000000000..ce7eca5d27
--- /dev/null
+++ b/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;
+}