diff --git a/llvm/include/llvm/TableGen/Record.h b/llvm/include/llvm/TableGen/Record.h
index 2853a471b67fc6..b71aa0a8905632 100644
--- a/llvm/include/llvm/TableGen/Record.h
+++ b/llvm/include/llvm/TableGen/Record.h
@@ -20,6 +20,7 @@
 #include "llvm/ADT/FoldingSet.h"
 #include "llvm/ADT/PointerIntPair.h"
 #include "llvm/ADT/SmallVector.h"
+#include "llvm/ADT/StringExtras.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/Support/Casting.h"
 #include "llvm/Support/ErrorHandling.h"
@@ -1866,8 +1867,6 @@ struct LessRecordFieldName {
 };
 
 struct LessRecordRegister {
-  static bool ascii_isdigit(char x) { return x >= '0' && x <= '9'; }
-
   struct RecordParts {
     SmallVector<std::pair< bool, StringRef>, 4> Parts;
 
@@ -1878,18 +1877,18 @@ struct LessRecordRegister {
       size_t Len = 0;
       const char *Start = Rec.data();
       const char *Curr = Start;
-      bool isDigitPart = ascii_isdigit(Curr[0]);
+      bool IsDigitPart = isDigit(Curr[0]);
       for (size_t I = 0, E = Rec.size(); I != E; ++I, ++Len) {
-        bool isDigit = ascii_isdigit(Curr[I]);
-        if (isDigit != isDigitPart) {
-          Parts.push_back(std::make_pair(isDigitPart, StringRef(Start, Len)));
+        bool IsDigit = isDigit(Curr[I]);
+        if (IsDigit != IsDigitPart) {
+          Parts.push_back(std::make_pair(IsDigitPart, StringRef(Start, Len)));
           Len = 0;
           Start = &Curr[I];
-          isDigitPart = ascii_isdigit(Curr[I]);
+          IsDigitPart = isDigit(Curr[I]);
         }
       }
       // Push the last part.
-      Parts.push_back(std::make_pair(isDigitPart, StringRef(Start, Len)));
+      Parts.push_back(std::make_pair(IsDigitPart, StringRef(Start, Len)));
     }
 
     size_t size() { return Parts.size(); }
diff --git a/llvm/lib/CodeGen/AsmPrinter/AsmPrinterInlineAsm.cpp b/llvm/lib/CodeGen/AsmPrinter/AsmPrinterInlineAsm.cpp
index 3a51134b494eaa..4a67b0bc2c4d40 100644
--- a/llvm/lib/CodeGen/AsmPrinter/AsmPrinterInlineAsm.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/AsmPrinterInlineAsm.cpp
@@ -234,7 +234,8 @@ static void EmitMSInlineAsmStr(const char *AsmStr, const MachineInstr *MI,
 
       const char *IDStart = LastEmitted;
       const char *IDEnd = IDStart;
-      while (*IDEnd >= '0' && *IDEnd <= '9') ++IDEnd;
+      while (isDigit(*IDEnd))
+        ++IDEnd;
 
       unsigned Val;
       if (StringRef(IDStart, IDEnd-IDStart).getAsInteger(10, Val))
@@ -399,7 +400,8 @@ static void EmitGCCInlineAsmStr(const char *AsmStr, const MachineInstr *MI,
 
       const char *IDStart = LastEmitted;
       const char *IDEnd = IDStart;
-      while (*IDEnd >= '0' && *IDEnd <= '9') ++IDEnd;
+      while (isDigit(*IDEnd))
+        ++IDEnd;
 
       unsigned Val;
       if (StringRef(IDStart, IDEnd-IDStart).getAsInteger(10, Val))
diff --git a/llvm/lib/CodeGen/TargetLoweringBase.cpp b/llvm/lib/CodeGen/TargetLoweringBase.cpp
index f639f7295b57f0..7aa569147da488 100644
--- a/llvm/lib/CodeGen/TargetLoweringBase.cpp
+++ b/llvm/lib/CodeGen/TargetLoweringBase.cpp
@@ -2077,7 +2077,7 @@ static bool parseRefinementStep(StringRef In, size_t &Position,
   // step parameter.
   if (RefStepString.size() == 1) {
     char RefStepChar = RefStepString[0];
-    if (RefStepChar >= '0' && RefStepChar <= '9') {
+    if (isDigit(RefStepChar)) {
       Value = RefStepChar - '0';
       return true;
     }
diff --git a/llvm/lib/DebugInfo/Symbolize/Symbolize.cpp b/llvm/lib/DebugInfo/Symbolize/Symbolize.cpp
index 4c3f3a3767e1d4..da157a5a255497 100644
--- a/llvm/lib/DebugInfo/Symbolize/Symbolize.cpp
+++ b/llvm/lib/DebugInfo/Symbolize/Symbolize.cpp
@@ -589,10 +589,8 @@ StringRef demanglePE32ExternCFunc(StringRef SymbolName) {
   if (Front != '?') {
     size_t AtPos = SymbolName.rfind('@');
     if (AtPos != StringRef::npos &&
-        all_of(drop_begin(SymbolName, AtPos + 1),
-               [](char C) { return C >= '0' && C <= '9'; })) {
+        all_of(drop_begin(SymbolName, AtPos + 1), isDigit))
       SymbolName = SymbolName.substr(0, AtPos);
-    }
   }
 
   // Remove any ending '@' for vectorcall.
diff --git a/llvm/lib/IR/AsmWriter.cpp b/llvm/lib/IR/AsmWriter.cpp
index 2b2456c3b479f0..69abf8769e4b2d 100644
--- a/llvm/lib/IR/AsmWriter.cpp
+++ b/llvm/lib/IR/AsmWriter.cpp
@@ -1368,9 +1368,8 @@ static void WriteConstantInternal(raw_ostream &Out, const Constant *CV,
         // "Inf" or NaN, that atof will accept, but the lexer will not.  Check
         // that the string matches the "[-+]?[0-9]" regex.
         //
-        assert(((StrVal[0] >= '0' && StrVal[0] <= '9') ||
-                ((StrVal[0] == '-' || StrVal[0] == '+') &&
-                 (StrVal[1] >= '0' && StrVal[1] <= '9'))) &&
+        assert((isDigit(StrVal[0]) || ((StrVal[0] == '-' || StrVal[0] == '+') &&
+                                       isDigit(StrVal[1]))) &&
                "[-+]?[0-9] regex does not match!");
         // Reparse stringized version!
         if (APFloat(APFloat::IEEEdouble(), StrVal).convertToDouble() == Val) {
diff --git a/llvm/lib/ProfileData/SampleProfReader.cpp b/llvm/lib/ProfileData/SampleProfReader.cpp
index e8ac06d8637ff7..c42931174bc038 100644
--- a/llvm/lib/ProfileData/SampleProfReader.cpp
+++ b/llvm/lib/ProfileData/SampleProfReader.cpp
@@ -144,7 +144,7 @@ static bool ParseLine(const StringRef &Input, LineType &LineTy, uint32_t &Depth,
   }
 
   StringRef Rest = Input.substr(n1 + 2);
-  if (Rest[0] >= '0' && Rest[0] <= '9') {
+  if (isDigit(Rest[0])) {
     LineTy = LineType::BodyProfile;
     size_t n3 = Rest.find(' ');
     if (n3 == StringRef::npos) {
diff --git a/llvm/lib/Support/Triple.cpp b/llvm/lib/Support/Triple.cpp
index 1483684dd8e591..4f483c965282d6 100644
--- a/llvm/lib/Support/Triple.cpp
+++ b/llvm/lib/Support/Triple.cpp
@@ -1038,7 +1038,7 @@ StringRef Triple::getOSAndEnvironmentName() const {
 }
 
 static unsigned EatNumber(StringRef &Str) {
-  assert(!Str.empty() && Str[0] >= '0' && Str[0] <= '9' && "Not a number");
+  assert(!Str.empty() && isDigit(Str[0]) && "Not a number");
   unsigned Result = 0;
 
   do {
@@ -1047,7 +1047,7 @@ static unsigned EatNumber(StringRef &Str) {
 
     // Eat the digit.
     Str = Str.substr(1);
-  } while (!Str.empty() && Str[0] >= '0' && Str[0] <= '9');
+  } while (!Str.empty() && isDigit(Str[0]));
 
   return Result;
 }