[PATCH] Allow isDereferencablePointer to look through BitCast ConstantExprs

[David Majnemer]

================
Comment at: lib/IR/Value.cpp:502-511
@@ +501,12 @@
+    
+    if (const BitCastInst *BC = dyn_cast<BitCastInst>(V)) {
+      SrcVal = BC->getOperand(0);
+      STy = BC->getSrcTy()->getPointerElementType();
+      DTy = BC->getDestTy()->getPointerElementType();
+    } else if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) {
+      if (CE->getOpcode() == Instruction::BitCast) {
+        SrcVal = CE->getOperand(0);
+        STy = SrcVal->getType()->getPointerElementType();
+        DTy = CE->getType()->getPointerElementType();
+      }
+    }
----------------
I think you can reduce the code duplication by using `Operator`: http://llvm.org/docs/doxygen/html/classllvm_1_1Operator.html

Perhaps:

  if (const auto *BC = dyn_cast<ConcreteOperator<Operator, Instruction::BitCast>>(V)) {
    SrcVal = BC->getOperand(0);
    STy = BC->getSrcTy()->getPointerElementType();
    DTy = BC->getDestTy()->getPointerElementType();
  }

http://reviews.llvm.org/D7411

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