diff --git a/llvm/include/llvm/IR/DerivedTypes.h b/llvm/include/llvm/IR/DerivedTypes.h
--- a/llvm/include/llvm/IR/DerivedTypes.h
+++ b/llvm/include/llvm/IR/DerivedTypes.h
@@ -520,12 +520,6 @@
     return EC;
   }
 
-  /// Return the minimum number of bits in the Vector type.
-  /// Returns zero when the vector is a vector of pointers.
-  unsigned getBitWidth() const {
-    return getNumElements() * getElementType()->getPrimitiveSizeInBits();
-  }
-
   /// Methods for support type inquiry through isa, cast, and dyn_cast.
   static bool classof(const Type *T) {
     return T->getTypeID() == FixedVectorTyID ||
diff --git a/llvm/lib/IR/Type.cpp b/llvm/lib/IR/Type.cpp
--- a/llvm/lib/IR/Type.cpp
+++ b/llvm/lib/IR/Type.cpp
@@ -68,20 +68,23 @@
     return false;
 
   // Vector -> Vector conversions are always lossless if the two vector types
-  // have the same size, otherwise not.  Also, 64-bit vector types can be
+  // have the same size, otherwise not.  Also, 64-bit fixed vector types can be
   // converted to x86mmx.
-  if (auto *thisPTy = dyn_cast<VectorType>(this)) {
-    if (auto *thatPTy = dyn_cast<VectorType>(Ty))
-      return thisPTy->getBitWidth() == thatPTy->getBitWidth();
-    if (Ty->getTypeID() == Type::X86_MMXTyID &&
-        thisPTy->getBitWidth() == 64)
+  if (isa<VectorType>(this)) {
+    TypeSize ThisTypeSize = getPrimitiveSizeInBits();
+    if (isa<VectorType>(Ty))
+      return ThisTypeSize == Ty->getPrimitiveSizeInBits();
+    if (Ty->getTypeID() == Type::X86_MMXTyID && !ThisTypeSize.isScalable() &&
+        ThisTypeSize.getFixedSize() == 64)
       return true;
   }
 
   if (this->getTypeID() == Type::X86_MMXTyID)
-    if (auto *thatPTy = dyn_cast<VectorType>(Ty))
-      if (thatPTy->getBitWidth() == 64)
+    if (isa<FixedVectorType>(Ty)) {
+      TypeSize ThatTypeSize = Ty->getPrimitiveSizeInBits();
+      if (ThatTypeSize.getFixedSize() == 64)
         return true;
+    }
 
   // At this point we have only various mismatches of the first class types
   // remaining and ptr->ptr. Just select the lossless conversions. Everything
@@ -126,7 +129,10 @@
   case Type::FixedVectorTyID:
   case Type::ScalableVectorTyID: {
     const VectorType *VTy = cast<VectorType>(this);
-    return TypeSize(VTy->getBitWidth(), isa<ScalableVectorType>(VTy));
+    ElementCount EC = VTy->getElementCount();
+    TypeSize ETS = VTy->getElementType()->getPrimitiveSizeInBits();
+    assert(!ETS.isScalable() && "Vector type should have fixed-width elements");
+    return {ETS.getFixedSize() * EC.Min, EC.Scalable};
   }
   default: return TypeSize::Fixed(0);
   }