Remove the bitcast (of global values) from load instructions.

Adds the eliding of bitcasts that are used as an argument to
instructions that expect normalized pointers. Currently, the checked
in code only checks normalized pointers for load instructions. Hence,
the restriction to load instructions. As more instructions are
modified to check for normalized pointers, this code will apply
to those instructions.

BUG= https://code.google.com/p/nativeclient/issues/detail?id=3544
R=mseaborn@chromium.org

Review URL: https://codereview.chromium.org/21614002

2 files changed, 28 insertions, 14 deletions

diff --git a/lib/Bitcode/NaCl/Reader/NaClBitcodeReader.cpp b/lib/Bitcode/NaCl/Reader/NaClBitcodeReader.cpp
index 40f8842b3b..ede06b2457 100644
--- a/lib/Bitcode/NaCl/Reader/NaClBitcodeReader.cpp
+++ b/lib/Bitcode/NaCl/Reader/NaClBitcodeReader.cpp
@@ -1315,28 +1315,28 @@ bool NaClBitcodeReader::InstallInstruction(
 }
 
 Value *NaClBitcodeReader::ConvertOpToType(Value *Op, Type *T, BasicBlock *BB) {
-  // Note: Currently only knows how to add inttoptr type conversion, since
-  // this is the only elided instruction in the bitcode writer.
+  // Note: Currently only knows how to add inttoptr and bitcast type
+  // conversions for non-phi nodes, since these are the only elided
+  // instructions in the bitcode writer.
+  //
   // TODO(kschimpf): Generalize this as we expand elided conversions.
-  Value *Conversion = 0;
+  Instruction *Conversion = 0;
   Type *OpTy = Op->getType();
   if (OpTy == T) return Op;
 
-  // Following while loop is only run once. It is used to break on
-  // erroneous conditions.
-  while (true) {
-    if (!OpTy->isIntegerTy()) break;
-    if (!T->isPointerTy()) break;
-    Instruction *I = CastInst::Create(Instruction::IntToPtr, Op, T);
-    if (InstallInstruction(BB, I)) break;
-    Conversion = I;
-    break;
+  if (OpTy->isPointerTy()) {
+    Conversion = new BitCastInst(Op, T);
+  } else if (OpTy->isIntegerTy()) {
+    Conversion = new IntToPtrInst(Op, T);
   }
+
   if (Conversion == 0) {
     std::string Message;
     raw_string_ostream StrM(Message);
     StrM << "Can't convert " << *Op << " to type " << *T << "\n";
     Error(StrM.str());
+  } else {
+    InstallInstruction(BB, Conversion);
   }
   return Conversion;
 }
diff --git a/lib/Bitcode/NaCl/Writer/NaClValueEnumerator.cpp b/lib/Bitcode/NaCl/Writer/NaClValueEnumerator.cpp
index 7da01f005e..11e1161bf8 100644
--- a/lib/Bitcode/NaCl/Writer/NaClValueEnumerator.cpp
+++ b/lib/Bitcode/NaCl/Writer/NaClValueEnumerator.cpp
@@ -450,7 +450,7 @@ static bool AllowsNormalizedPtr(const Value *V, const Instruction *Arg) {
 // Returns true if the bitcode reader and writer can assume that the
 // uses of the given inttotpr I2P allow normalized pointers (as
 // defined in llvm/lib/Transforms/NaCl/ReplacePtrsWithInts.cpp).
-static bool IntToPtrUsesAllowEliding(const Instruction *I2P) {
+static bool AllUsesAllowNormalizedPtr(const Instruction *I2P) {
   for (Value::const_use_iterator u = I2P->use_begin(), e = I2P->use_end();
        u != e; ++u) {
     if (!AllowsNormalizedPtr(cast<Value>(*u), I2P)) return false;
@@ -461,6 +461,12 @@ static bool IntToPtrUsesAllowEliding(const Instruction *I2P) {
   return true;
 }
 
+// Returns true if the value is an InherentPtr (as defined in
+// llvm/lib/Transforms/NaCl/ReplacePtrsWithInts.cpp).
+static inline bool IsInherentPtr(const Value *V) {
+  return isa<AllocaInst>(V) || isa<GlobalValue>(V);
+}
+
 // Note: This function is based on the comments in
 // llvm/lib/Transforms/NaCl/ReplacePtrsWithInts.cpp.
 const Value *NaClValueEnumerator::ElideCasts(const Value *V) {
@@ -470,10 +476,18 @@ const Value *NaClValueEnumerator::ElideCasts(const Value *V) {
     switch (I->getOpcode()) {
     default:
       break;
+    case Instruction::BitCast:
+      if (I->getType()->isPointerTy() &&
+	  AllUsesAllowNormalizedPtr(I) &&
+	  IsInherentPtr(I->getOperand(0))) {
+	return ElideCasts(I->getOperand(0));
+      }
+      break;
     case Instruction::IntToPtr:
-      if (IntToPtrUsesAllowEliding(I)) {
+      if (AllUsesAllowNormalizedPtr(I)) {
         return ElideCasts(I->getOperand(0));
       }
+      break;
     }
   }
   return V;