diff --git a/llvm/include/llvm/Demangle/ItaniumDemangle.h b/llvm/include/llvm/Demangle/ItaniumDemangle.h
--- a/llvm/include/llvm/Demangle/ItaniumDemangle.h
+++ b/llvm/include/llvm/Demangle/ItaniumDemangle.h
@@ -2349,7 +2349,7 @@
 #endif
       char num[FloatData<Float>::max_demangled_size] = {0};
       int n = snprintf(num, sizeof(num), FloatData<Float>::spec, value);
-      OB += StringView(num, num + n);
+      OB += StringView(num, n);
     }
   }
 };
@@ -2477,7 +2477,7 @@
   }
 
   bool consumeIf(StringView S) {
-    if (StringView(First, Last).startsWith(S)) {
+    if (StringView(First, Last - First).startsWith(S)) {
       First += S.size();
       return true;
     }
@@ -2933,7 +2933,7 @@
     return nullptr;
   if (numLeft() < Length || Length == 0)
     return nullptr;
-  StringView Name(First, First + Length);
+  StringView Name(First, Length);
   First += Length;
   if (Name.startsWith("_GLOBAL__N"))
     return make<NameType>("(anonymous namespace)");
@@ -3470,7 +3470,7 @@
     return StringView();
   while (numLeft() != 0 && std::isdigit(*First))
     ++First;
-  return StringView(Tmp, First);
+  return StringView(Tmp, First - Tmp);
 }
 
 // <positive length number> ::= [0-9]*
@@ -3491,7 +3491,7 @@
   size_t Int = 0;
   if (parsePositiveInteger(&Int) || numLeft() < Int)
     return StringView();
-  StringView R(First, First + Int);
+  StringView R(First, Int);
   First += Int;
   return R;
 }
@@ -5143,7 +5143,7 @@
   const size_t N = FloatData<Float>::mangled_size;
   if (numLeft() <= N)
     return nullptr;
-  StringView Data(First, First + N);
+  StringView Data(First, N);
   for (char C : Data)
     if (!std::isxdigit(C))
       return nullptr;
@@ -5463,7 +5463,7 @@
     if (Encoding == nullptr)
       return nullptr;
     if (look() == '.') {
-      Encoding = make<DotSuffix>(Encoding, StringView(First, Last));
+      Encoding = make<DotSuffix>(Encoding, StringView(First, Last - First));
       First = Last;
     }
     if (numLeft() != 0)
diff --git a/llvm/include/llvm/Demangle/StringView.h b/llvm/include/llvm/Demangle/StringView.h
--- a/llvm/include/llvm/Demangle/StringView.h
+++ b/llvm/include/llvm/Demangle/StringView.h
@@ -31,8 +31,6 @@
 
   template <size_t N>
   StringView(const char (&Str)[N]) : First(Str), Last(Str + N - 1) {}
-  StringView(const char *First_, const char *Last_)
-      : First(First_), Last(Last_) {}
   StringView(const char *First_, size_t Len)
       : First(First_), Last(First_ + Len) {}
   StringView(const char *Str) : First(Str), Last(Str + std::strlen(Str)) {}
diff --git a/llvm/include/llvm/Demangle/Utility.h b/llvm/include/llvm/Demangle/Utility.h
--- a/llvm/include/llvm/Demangle/Utility.h
+++ b/llvm/include/llvm/Demangle/Utility.h
@@ -64,7 +64,7 @@
     if (isNeg)
       *--TempPtr = '-';
 
-    return operator+=(StringView(TempPtr, Temp.data() + Temp.size()));
+    return operator+=(StringView(TempPtr, Temp.data() + Temp.size() - TempPtr));
   }
 
 public:
diff --git a/llvm/lib/Demangle/MicrosoftDemangle.cpp b/llvm/lib/Demangle/MicrosoftDemangle.cpp
--- a/llvm/lib/Demangle/MicrosoftDemangle.cpp
+++ b/llvm/lib/Demangle/MicrosoftDemangle.cpp
@@ -779,7 +779,7 @@
   //    either.
   MangledName.consumeFront("??_R4@");
 
-  StringView MD5(Start, MangledName.begin());
+  StringView MD5(Start, MangledName.begin() - Start);
   SymbolNode *S = Arena.alloc<SymbolNode>(NodeKind::Md5Symbol);
   S->Name = synthesizeQualifiedName(Arena, MD5);
 
diff --git a/llvm/lib/Demangle/RustDemangle.cpp b/llvm/lib/Demangle/RustDemangle.cpp
--- a/llvm/lib/Demangle/RustDemangle.cpp
+++ b/llvm/lib/Demangle/RustDemangle.cpp
@@ -1122,7 +1122,7 @@
         return false;
       // Code points are padded with zeros while decoding is in progress.
       char UTF8[4] = {C};
-      Output += StringView(UTF8, UTF8 + 4);
+      Output += StringView(UTF8, 4);
     }
     // Skip over the delimiter.
     ++InputIdx;