diff --git a/llvm/include/llvm/IR/InstrTypes.h b/llvm/include/llvm/IR/InstrTypes.h
--- a/llvm/include/llvm/IR/InstrTypes.h
+++ b/llvm/include/llvm/IR/InstrTypes.h
@@ -599,12 +599,6 @@
     BasicBlock *InsertAtEnd  ///< The block to insert the instruction into
   );
 
-  /// Check whether it is valid to call getCastOpcode for these types.
-  static bool isCastable(
-    Type *SrcTy, ///< The Type from which the value should be cast.
-    Type *DestTy ///< The Type to which the value should be cast.
-  );
-
   /// Check whether a bitcast between these types is valid
   static bool isBitCastable(
     Type *SrcTy, ///< The Type from which the value should be cast.
diff --git a/llvm/lib/IR/Instructions.cpp b/llvm/lib/IR/Instructions.cpp
--- a/llvm/lib/IR/Instructions.cpp
+++ b/llvm/lib/IR/Instructions.cpp
@@ -3142,64 +3142,6 @@
   return Create(opcode, C, Ty, Name, InsertAtEnd);
 }
 
-// Check whether it is valid to call getCastOpcode for these types.
-// This routine must be kept in sync with getCastOpcode.
-bool CastInst::isCastable(Type *SrcTy, Type *DestTy) {
-  if (!SrcTy->isFirstClassType() || !DestTy->isFirstClassType())
-    return false;
-
-  if (SrcTy == DestTy)
-    return true;
-
-  if (VectorType *SrcVecTy = dyn_cast<VectorType>(SrcTy))
-    if (VectorType *DestVecTy = dyn_cast<VectorType>(DestTy))
-      if (cast<FixedVectorType>(SrcVecTy)->getNumElements() ==
-          cast<FixedVectorType>(DestVecTy)->getNumElements()) {
-        // An element by element cast.  Valid if casting the elements is valid.
-        SrcTy = SrcVecTy->getElementType();
-        DestTy = DestVecTy->getElementType();
-      }
-
-  // Get the bit sizes, we'll need these
-  TypeSize SrcBits = SrcTy->getPrimitiveSizeInBits();   // 0 for ptr
-  TypeSize DestBits = DestTy->getPrimitiveSizeInBits(); // 0 for ptr
-
-  // Run through the possibilities ...
-  if (DestTy->isIntegerTy()) {               // Casting to integral
-    if (SrcTy->isIntegerTy())                // Casting from integral
-        return true;
-    if (SrcTy->isFloatingPointTy())   // Casting from floating pt
-      return true;
-    if (SrcTy->isVectorTy())          // Casting from vector
-      return DestBits == SrcBits;
-                                      // Casting from something else
-    return SrcTy->isPointerTy();
-  }
-  if (DestTy->isFloatingPointTy()) {  // Casting to floating pt
-    if (SrcTy->isIntegerTy())                // Casting from integral
-      return true;
-    if (SrcTy->isFloatingPointTy())   // Casting from floating pt
-      return true;
-    if (SrcTy->isVectorTy())          // Casting from vector
-      return DestBits == SrcBits;
-                                    // Casting from something else
-    return false;
-  }
-  if (DestTy->isVectorTy())         // Casting to vector
-    return DestBits == SrcBits;
-  if (DestTy->isPointerTy()) {        // Casting to pointer
-    if (SrcTy->isPointerTy())                // Casting from pointer
-      return true;
-    return SrcTy->isIntegerTy();             // Casting from integral
-  }
-  if (DestTy->isX86_MMXTy()) {
-    if (SrcTy->isVectorTy())
-      return DestBits == SrcBits;       // 64-bit vector to MMX
-    return false;
-  }                                    // Casting to something else
-  return false;
-}
-
 bool CastInst::isBitCastable(Type *SrcTy, Type *DestTy) {
   if (!SrcTy->isFirstClassType() || !DestTy->isFirstClassType())
     return false;
@@ -3261,7 +3203,6 @@
 //   castIsValid( getCastOpcode(Val, Ty), Val, Ty)
 // should not assert in castIsValid. In other words, this produces a "correct"
 // casting opcode for the arguments passed to it.
-// This routine must be kept in sync with isCastable.
 Instruction::CastOps
 CastInst::getCastOpcode(
   const Value *Src, bool SrcIsSigned, Type *DestTy, bool DestIsSigned) {
diff --git a/llvm/unittests/IR/InstructionsTest.cpp b/llvm/unittests/IR/InstructionsTest.cpp
--- a/llvm/unittests/IR/InstructionsTest.cpp
+++ b/llvm/unittests/IR/InstructionsTest.cpp
@@ -229,11 +229,6 @@
 
   const Constant *v2ptr32 = Constant::getNullValue(V2Int32PtrTy);
 
-  EXPECT_TRUE(CastInst::isCastable(V8x8Ty, X86MMXTy));
-  EXPECT_TRUE(CastInst::isCastable(X86MMXTy, V8x8Ty));
-  EXPECT_FALSE(CastInst::isCastable(Int64Ty, X86MMXTy));
-  EXPECT_TRUE(CastInst::isCastable(V8x64Ty, V8x8Ty));
-  EXPECT_TRUE(CastInst::isCastable(V8x8Ty, V8x64Ty));
   EXPECT_EQ(CastInst::Trunc, CastInst::getCastOpcode(c64, true, V8x8Ty, true));
   EXPECT_EQ(CastInst::SExt, CastInst::getCastOpcode(c8, true, V8x64Ty, true));
 
@@ -249,7 +244,6 @@
   EXPECT_FALSE(CastInst::isBitCastable(V2Int32PtrTy, V2Int32PtrAS1Ty));
   EXPECT_FALSE(CastInst::isBitCastable(V2Int32PtrAS1Ty, V2Int32PtrTy));
   EXPECT_TRUE(CastInst::isBitCastable(V2Int32PtrAS1Ty, V2Int64PtrAS1Ty));
-  EXPECT_TRUE(CastInst::isCastable(V2Int32PtrAS1Ty, V2Int32PtrTy));
   EXPECT_EQ(CastInst::AddrSpaceCast, CastInst::getCastOpcode(v2ptr32, true,
                                                              V2Int32PtrAS1Ty,
                                                              true));