diff --git a/clang-tools-extra/clang-tidy/readability/IdentifierNamingCheck.cpp b/clang-tools-extra/clang-tidy/readability/IdentifierNamingCheck.cpp
index eeb0642baa100..9561b2b00904f 100644
--- a/clang-tools-extra/clang-tidy/readability/IdentifierNamingCheck.cpp
+++ b/clang-tools-extra/clang-tidy/readability/IdentifierNamingCheck.cpp
@@ -337,10 +337,10 @@ std::string IdentifierNamingCheck::HungarianNotation::getDeclTypeName(
         Type.replace(Pos, Kw.size(), "");
       }
     }
-    TypeName = Type.erase(0, Type.find_first_not_of(" "));
+    TypeName = Type.erase(0, Type.find_first_not_of(' '));
 
     // Remove template parameters
-    const size_t Pos = Type.find("<");
+    const size_t Pos = Type.find('<');
     if (Pos != std::string::npos) {
       TypeName = Type.erase(Pos, Type.size() - Pos);
     }
@@ -377,14 +377,14 @@ std::string IdentifierNamingCheck::HungarianNotation::getDeclTypeName(
       }
     }
 
-    TypeName = Type.erase(0, Type.find_first_not_of(" "));
+    TypeName = Type.erase(0, Type.find_first_not_of(' '));
     if (!RedundantRemoved) {
-      std::size_t FoundSpace = Type.find(" ");
+      std::size_t FoundSpace = Type.find(' ');
       if (FoundSpace != std::string::npos)
         Type = Type.substr(0, FoundSpace);
     }
 
-    TypeName = Type.erase(0, Type.find_first_not_of(" "));
+    TypeName = Type.erase(0, Type.find_first_not_of(' '));
 
     QualType QT = VD->getType();
     if (!QT.isNull() && QT->isArrayType())
@@ -586,7 +586,7 @@ std::string IdentifierNamingCheck::HungarianNotation::getDataTypePrefix(
       if (PrefixStr.empty())
         PrefixStr = HNOption.DerivedType.lookup("Array");
     } else if (QT->isReferenceType()) {
-      size_t Pos = ModifiedTypeName.find_last_of("&");
+      size_t Pos = ModifiedTypeName.find_last_of('&');
       if (Pos != std::string::npos)
         ModifiedTypeName = ModifiedTypeName.substr(0, Pos);
     }
@@ -653,7 +653,7 @@ std::string IdentifierNamingCheck::HungarianNotation::getEnumPrefix(
   std::string Name = ED->getName().str();
   if (std::string::npos != Name.find("enum")) {
     Name = Name.substr(strlen("enum"), Name.length() - strlen("enum"));
-    Name = Name.erase(0, Name.find_first_not_of(" "));
+    Name = Name.erase(0, Name.find_first_not_of(' '));
   }
 
   static llvm::Regex Splitter(
diff --git a/flang/lib/Semantics/check-io.cpp b/flang/lib/Semantics/check-io.cpp
index 6df5eadc8ae62..1c1b07c422bac 100644
--- a/flang/lib/Semantics/check-io.cpp
+++ b/flang/lib/Semantics/check-io.cpp
@@ -101,7 +101,7 @@ void IoChecker::Enter(const parser::ConnectSpec &spec) {
 // Ignore trailing spaces (12.5.6.2 p1) and convert to upper case
 static std::string Normalize(const std::string &value) {
   auto upper{parser::ToUpperCaseLetters(value)};
-  std::size_t lastNonBlank{upper.find_last_not_of(" ")};
+  std::size_t lastNonBlank{upper.find_last_not_of(' ')};
   upper.resize(lastNonBlank == std::string::npos ? 0 : lastNonBlank + 1);
   return upper;
 }
diff --git a/lldb/source/Plugins/Process/Linux/IntelPTCollector.cpp b/lldb/source/Plugins/Process/Linux/IntelPTCollector.cpp
index 277fec9f7116e..a38b75c9e615f 100644
--- a/lldb/source/Plugins/Process/Linux/IntelPTCollector.cpp
+++ b/lldb/source/Plugins/Process/Linux/IntelPTCollector.cpp
@@ -81,7 +81,7 @@ static std::optional<int> GetCGroupFileDescriptor(lldb::pid_t pid) {
     if (line.find("0:") != 0)
       continue;
 
-    std::string slice = line.substr(line.find_first_of("/"));
+    std::string slice = line.substr(line.find_first_of('/'));
     if (slice.empty())
       return std::nullopt;
     std::string cgroup_file = formatv("/sys/fs/cgroup/{0}", slice);
diff --git a/llvm/lib/Transforms/Instrumentation/DataFlowSanitizer.cpp b/llvm/lib/Transforms/Instrumentation/DataFlowSanitizer.cpp
index bfa748e7a6950..ccb7a37c83d54 100644
--- a/llvm/lib/Transforms/Instrumentation/DataFlowSanitizer.cpp
+++ b/llvm/lib/Transforms/Instrumentation/DataFlowSanitizer.cpp
@@ -1256,7 +1256,7 @@ void DataFlowSanitizer::addGlobalNameSuffix(GlobalValue *GV) {
   size_t Pos = Asm.find(SearchStr);
   if (Pos != std::string::npos) {
     Asm.replace(Pos, SearchStr.size(), ".symver " + GVName + Suffix + ",");
-    Pos = Asm.find("@");
+    Pos = Asm.find('@');
 
     if (Pos == std::string::npos)
       report_fatal_error(Twine("unsupported .symver: ", Asm));