1 files changed, 28 insertions, 38 deletions

diff --git a/lib/IR/Value.cpp b/lib/IR/Value.cpp
index d734e4e..35c241a 100644
--- a/lib/IR/Value.cpp
+++ b/lib/IR/Value.cpp
@@ -17,6 +17,7 @@
 #include "llvm/ADT/SmallString.h"
 #include "llvm/IR/Constant.h"
 #include "llvm/IR/Constants.h"
+#include "llvm/IR/DataLayout.h"
 #include "llvm/IR/DerivedTypes.h"
 #include "llvm/IR/GetElementPtrTypeIterator.h"
 #include "llvm/IR/InstrTypes.h"
@@ -38,13 +39,12 @@ using namespace llvm;
 
 static inline Type *checkType(Type *Ty) {
   assert(Ty && "Value defined with a null type: Error!");
-  return const_cast<Type*>(Ty);
+  return Ty;
 }
 
 Value::Value(Type *ty, unsigned scid)
-  : SubclassID(scid), HasValueHandle(0),
-    SubclassOptionalData(0), SubclassData(0), VTy((Type*)checkType(ty)),
-    UseList(nullptr), Name(nullptr) {
+    : VTy(checkType(ty)), UseList(nullptr), Name(nullptr), SubclassID(scid),
+      HasValueHandle(0), SubclassOptionalData(0), SubclassData(0) {
   // FIXME: Why isn't this in the subclass gunk??
   // Note, we cannot call isa<CallInst> before the CallInst has been
   // constructed.
@@ -214,7 +214,7 @@ void Value::setName(const Twine &NewName) {
     // then reallocated.
 
     // Create the new name.
-    Name = ValueName::Create(NameRef.begin(), NameRef.end());
+    Name = ValueName::Create(NameRef);
     Name->setValue(this);
     return;
   }
@@ -301,27 +301,6 @@ void Value::takeName(Value *V) {
     ST->reinsertValue(this);
 }
 
-static GlobalObject &findReplacementForAliasUse(Value &C) {
-  if (auto *GO = dyn_cast<GlobalObject>(&C))
-    return *GO;
-  if (auto *GA = dyn_cast<GlobalAlias>(&C))
-    return *GA->getAliasee();
-  auto *CE = cast<ConstantExpr>(&C);
-  assert(CE->getOpcode() == Instruction::BitCast ||
-         CE->getOpcode() == Instruction::GetElementPtr ||
-         CE->getOpcode() == Instruction::AddrSpaceCast);
-  if (CE->getOpcode() == Instruction::GetElementPtr)
-    assert(cast<GEPOperator>(CE)->hasAllZeroIndices());
-  return findReplacementForAliasUse(*CE->getOperand(0));
-}
-
-static void replaceAliasUseWith(Use &U, Value *New) {
-  GlobalObject &Replacement = findReplacementForAliasUse(*New);
-  assert(&cast<GlobalObject>(*U) != &Replacement &&
-         "replaceAliasUseWith cannot form an alias cycle");
-  U.set(&Replacement);
-}
-
 #ifndef NDEBUG
 static bool contains(SmallPtrSet<ConstantExpr *, 4> &Cache, ConstantExpr *Expr,
                      Constant *C) {
@@ -373,10 +352,6 @@ void Value::replaceAllUsesWith(Value *New) {
     // Must handle Constants specially, we cannot call replaceUsesOfWith on a
     // constant because they are uniqued.
     if (auto *C = dyn_cast<Constant>(U.getUser())) {
-      if (isa<GlobalAlias>(C)) {
-        replaceAliasUseWith(U, New);
-        continue;
-      }
       if (!isa<GlobalValue>(C)) {
         C->replaceUsesOfWithOnConstant(this, New, &U);
         continue;
@@ -498,18 +473,33 @@ Value *Value::stripInBoundsOffsets() {
 
 /// isDereferenceablePointer - Test if this value is always a pointer to
 /// allocated and suitably aligned memory for a simple load or store.
-static bool isDereferenceablePointer(const Value *V,
+static bool isDereferenceablePointer(const Value *V, const DataLayout *DL,
                                      SmallPtrSet<const Value *, 32> &Visited) {
   // Note that it is not safe to speculate into a malloc'd region because
   // malloc may return null.
-  // It's also not always safe to follow a bitcast, for example:
-  //   bitcast i8* (alloca i8) to i32*
-  // would result in a 4-byte load from a 1-byte alloca. Some cases could
-  // be handled using DataLayout to check sizes and alignments though.
 
   // These are obviously ok.
   if (isa<AllocaInst>(V)) return true;
 
+  // It's not always safe to follow a bitcast, for example:
+  //   bitcast i8* (alloca i8) to i32*
+  // would result in a 4-byte load from a 1-byte alloca. However,
+  // if we're casting from a pointer from a type of larger size
+  // to a type of smaller size (or the same size), and the alignment
+  // is at least as large as for the resulting pointer type, then
+  // we can look through the bitcast.
+  if (DL)
+    if (const BitCastInst* BC = dyn_cast<BitCastInst>(V)) {
+      Type *STy = BC->getSrcTy()->getPointerElementType(),
+           *DTy = BC->getDestTy()->getPointerElementType();
+      if (STy->isSized() && DTy->isSized() &&
+          (DL->getTypeStoreSize(STy) >=
+           DL->getTypeStoreSize(DTy)) &&
+          (DL->getABITypeAlignment(STy) >=
+           DL->getABITypeAlignment(DTy)))
+        return isDereferenceablePointer(BC->getOperand(0), DL, Visited);
+    }
+
   // Global variables which can't collapse to null are ok.
   if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(V))
     return !GV->hasExternalWeakLinkage();
@@ -523,7 +513,7 @@ static bool isDereferenceablePointer(const Value *V,
     // Conservatively require that the base pointer be fully dereferenceable.
     if (!Visited.insert(GEP->getOperand(0)))
       return false;
-    if (!isDereferenceablePointer(GEP->getOperand(0), Visited))
+    if (!isDereferenceablePointer(GEP->getOperand(0), DL, Visited))
       return false;
     // Check the indices.
     gep_type_iterator GTI = gep_type_begin(GEP);
@@ -559,9 +549,9 @@ static bool isDereferenceablePointer(const Value *V,
 
 /// isDereferenceablePointer - Test if this value is always a pointer to
 /// allocated and suitably aligned memory for a simple load or store.
-bool Value::isDereferenceablePointer() const {
+bool Value::isDereferenceablePointer(const DataLayout *DL) const {
   SmallPtrSet<const Value *, 32> Visited;
-  return ::isDereferenceablePointer(this, Visited);
+  return ::isDereferenceablePointer(this, DL, Visited);
 }
 
 /// DoPHITranslation - If this value is a PHI node with CurBB as its parent,