diff --git a/clang-tools-extra/clang-tidy/bugprone/UncheckedOptionalAccessCheck.cpp b/clang-tools-extra/clang-tidy/bugprone/UncheckedOptionalAccessCheck.cpp
index 183beb6bfb87d..0a0e212f345ed 100644
--- a/clang-tools-extra/clang-tidy/bugprone/UncheckedOptionalAccessCheck.cpp
+++ b/clang-tools-extra/clang-tidy/bugprone/UncheckedOptionalAccessCheck.cpp
@@ -13,10 +13,8 @@
 #include "clang/Analysis/FlowSensitive/DataflowAnalysis.h"
 #include "clang/Analysis/FlowSensitive/Models/UncheckedOptionalAccessModel.h"
 #include "clang/Basic/SourceLocation.h"
+#include "llvm/ADT/SmallVector.h"
 #include "llvm/Support/Error.h"
-#include <memory>
-#include <optional>
-#include <vector>
 
 namespace clang::tidy::bugprone {
 using ast_matchers::MatchFinder;
@@ -54,7 +52,7 @@ void UncheckedOptionalAccessCheck::check(
   UncheckedOptionalAccessDiagnoser Diagnoser(ModelOptions);
   // FIXME: Allow user to set the (defaulted) SAT iterations max for
   // `diagnoseFunction` with config options.
-  if (llvm::Expected<std::vector<SourceLocation>> Locs =
+  if (llvm::Expected<llvm::SmallVector<SourceLocation>> Locs =
           dataflow::diagnoseFunction<UncheckedOptionalAccessModel,
                                      SourceLocation>(*FuncDecl, *Result.Context,
                                                      Diagnoser))
diff --git a/clang/include/clang/Analysis/FlowSensitive/DataflowAnalysis.h b/clang/include/clang/Analysis/FlowSensitive/DataflowAnalysis.h
index abd34f4092212..dd1a685cb48ba 100644
--- a/clang/include/clang/Analysis/FlowSensitive/DataflowAnalysis.h
+++ b/clang/include/clang/Analysis/FlowSensitive/DataflowAnalysis.h
@@ -31,6 +31,7 @@
 #include "llvm/ADT/Any.h"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/STLFunctionalExtras.h"
+#include "llvm/ADT/SmallVector.h"
 #include "llvm/Support/Errc.h"
 #include "llvm/Support/Error.h"
 
@@ -246,9 +247,9 @@ runDataflowAnalysis(
 /// - This limit is still low enough to keep runtimes acceptable (on typical
 ///   machines) in cases where we hit the limit.
 template <typename AnalysisT, typename Diagnostic>
-llvm::Expected<std::vector<Diagnostic>> diagnoseFunction(
+llvm::Expected<llvm::SmallVector<Diagnostic>> diagnoseFunction(
     const FunctionDecl &FuncDecl, ASTContext &ASTCtx,
-    llvm::function_ref<std::vector<Diagnostic>(
+    llvm::function_ref<llvm::SmallVector<Diagnostic>(
         const CFGElement &, ASTContext &,
         const TransferStateForDiagnostics<typename AnalysisT::Lattice> &)>
         Diagnoser,
@@ -263,7 +264,7 @@ llvm::Expected<std::vector<Diagnostic>> diagnoseFunction(
   DataflowAnalysisContext AnalysisContext(std::move(OwnedSolver));
   Environment Env(AnalysisContext, FuncDecl);
   AnalysisT Analysis(ASTCtx);
-  std::vector<Diagnostic> Diagnostics;
+  llvm::SmallVector<Diagnostic> Diagnostics;
   if (llvm::Error Err =
           runTypeErasedDataflowAnalysis(
               *Context, Analysis, Env,
diff --git a/clang/include/clang/Analysis/FlowSensitive/Models/UncheckedOptionalAccessModel.h b/clang/include/clang/Analysis/FlowSensitive/Models/UncheckedOptionalAccessModel.h
index 76a567f1399cd..aeaf75b215422 100644
--- a/clang/include/clang/Analysis/FlowSensitive/Models/UncheckedOptionalAccessModel.h
+++ b/clang/include/clang/Analysis/FlowSensitive/Models/UncheckedOptionalAccessModel.h
@@ -21,7 +21,7 @@
 #include "clang/Analysis/FlowSensitive/DataflowEnvironment.h"
 #include "clang/Analysis/FlowSensitive/NoopLattice.h"
 #include "clang/Basic/SourceLocation.h"
-#include <vector>
+#include "llvm/ADT/SmallVector.h"
 
 namespace clang {
 namespace dataflow {
@@ -74,14 +74,14 @@ class UncheckedOptionalAccessDiagnoser {
   UncheckedOptionalAccessDiagnoser(
       UncheckedOptionalAccessModelOptions Options = {});
 
-  std::vector<SourceLocation>
+  llvm::SmallVector<SourceLocation>
   operator()(const CFGElement &Elt, ASTContext &Ctx,
              const TransferStateForDiagnostics<NoopLattice> &State) {
     return DiagnoseMatchSwitch(Elt, Ctx, State.Env);
   }
 
 private:
-  CFGMatchSwitch<const Environment, std::vector<SourceLocation>>
+  CFGMatchSwitch<const Environment, llvm::SmallVector<SourceLocation>>
       DiagnoseMatchSwitch;
 };
 
diff --git a/clang/lib/Analysis/FlowSensitive/Models/UncheckedOptionalAccessModel.cpp b/clang/lib/Analysis/FlowSensitive/Models/UncheckedOptionalAccessModel.cpp
index e40bd3d0199bd..f61f26ff27804 100644
--- a/clang/lib/Analysis/FlowSensitive/Models/UncheckedOptionalAccessModel.cpp
+++ b/clang/lib/Analysis/FlowSensitive/Models/UncheckedOptionalAccessModel.cpp
@@ -34,7 +34,6 @@
 #include <memory>
 #include <optional>
 #include <utility>
-#include <vector>
 
 namespace clang {
 namespace dataflow {
@@ -913,8 +912,8 @@ auto buildTransferMatchSwitch() {
       .Build();
 }
 
-std::vector<SourceLocation> diagnoseUnwrapCall(const Expr *ObjectExpr,
-                                               const Environment &Env) {
+llvm::SmallVector<SourceLocation> diagnoseUnwrapCall(const Expr *ObjectExpr,
+                                                     const Environment &Env) {
   if (auto *OptionalVal = getValueBehindPossiblePointer(*ObjectExpr, Env)) {
     auto *Prop = OptionalVal->getProperty("has_value");
     if (auto *HasValueVal = cast_or_null<BoolValue>(Prop)) {
@@ -935,7 +934,8 @@ auto buildDiagnoseMatchSwitch(
   // lot of duplicated work (e.g. string comparisons), consider providing APIs
   // that avoid it through memoization.
   auto IgnorableOptional = ignorableOptional(Options);
-  return CFGMatchSwitchBuilder<const Environment, std::vector<SourceLocation>>()
+  return CFGMatchSwitchBuilder<const Environment,
+                               llvm::SmallVector<SourceLocation>>()
       // optional::value
       .CaseOfCFGStmt<CXXMemberCallExpr>(
           valueCall(IgnorableOptional),
diff --git a/clang/unittests/Analysis/FlowSensitive/TypeErasedDataflowAnalysisTest.cpp b/clang/unittests/Analysis/FlowSensitive/TypeErasedDataflowAnalysisTest.cpp
index af34a2afd2468..3fc1bb6692acf 100644
--- a/clang/unittests/Analysis/FlowSensitive/TypeErasedDataflowAnalysisTest.cpp
+++ b/clang/unittests/Analysis/FlowSensitive/TypeErasedDataflowAnalysisTest.cpp
@@ -98,7 +98,7 @@ TEST(DataflowAnalysisTest, DiagnoseFunctionDiagnoserCalledOnEachElement) {
       cast<FunctionDecl>(findValueDecl(AST->getASTContext(), "target"));
   auto Diagnoser = [](const CFGElement &Elt, ASTContext &,
                       const TransferStateForDiagnostics<NoopLattice> &) {
-    std::vector<std::string> Diagnostics(1);
+    llvm::SmallVector<std::string> Diagnostics(1);
     llvm::raw_string_ostream OS(Diagnostics.front());
     Elt.dumpToStream(OS);
     return Diagnostics;