Index: include/clang/Tooling/Tooling.h
===================================================================
--- include/clang/Tooling/Tooling.h
+++ include/clang/Tooling/Tooling.h
@@ -417,6 +417,27 @@
 /// \param File Either an absolute or relative path.
 std::string getAbsolutePath(StringRef File);
 
+/// \brief Changes CommandLine to contain implicit flags that would have been
+/// defined had the compiler driver been invoked through the path InvokedAs.
+///
+/// For example, when called with \c InvokedAs set to `i686-linux-android-g++`,
+/// the arguments '-target', 'i686-linux-android`, `--driver-mode=g++` will
+/// be inserted after the first argument in \c CommandLine.
+///
+/// This function will not add new `-target` or `--driver-mode` flags if they
+/// are already present in `CommandLine` (even if they have different settings
+/// than would have been inserted).
+///
+/// \pre `llvm::InitializeAllTargets()` has been called.
+///
+/// \param CommandLine the command line used to invoke the compiler driver or
+/// Clang tool, including the path to the executable as \c CommandLine[0].
+/// \param InvokedAs the path to the driver used to infer implicit flags.
+///
+/// \note This will not set \c CommandLine[0] to \c InvokedAs.
+void addTargetAndModeForProgramName(std::vector<std::string> &CommandLine,
+                                    StringRef InvokedAs);
+
 /// \brief Creates a \c CompilerInvocation.
 clang::CompilerInvocation *newInvocation(
     clang::DiagnosticsEngine *Diagnostics,
Index: lib/Tooling/Tooling.cpp
===================================================================
--- lib/Tooling/Tooling.cpp
+++ lib/Tooling/Tooling.cpp
@@ -17,6 +17,7 @@
 #include "clang/Driver/Compilation.h"
 #include "clang/Driver/Driver.h"
 #include "clang/Driver/Tool.h"
+#include "clang/Driver/ToolChain.h"
 #include "clang/Frontend/ASTUnit.h"
 #include "clang/Frontend/CompilerInstance.h"
 #include "clang/Frontend/FrontendDiagnostic.h"
@@ -162,6 +163,31 @@
   return AbsolutePath.str();
 }
 
+void addTargetAndModeForProgramName(std::vector<std::string> &CommandLine,
+                                    StringRef InvokedAs) {
+  if (!CommandLine.empty() && !InvokedAs.empty()) {
+    bool AlreadyHasTarget = false;
+    bool AlreadyHasMode = false;
+    // Skip CommandLine[0].
+    for (auto Token = ++CommandLine.begin(); Token != CommandLine.end();
+         ++Token) {
+      StringRef TokenRef(*Token);
+      AlreadyHasTarget |=
+          (TokenRef == "-target" || TokenRef.startswith("-target="));
+      AlreadyHasMode |= (TokenRef == "--driver-mode" ||
+                         TokenRef.startswith("--driver-mode="));
+    }
+    auto TargetMode =
+        clang::driver::ToolChain::getTargetAndModeFromProgramName(InvokedAs);
+    if (!AlreadyHasMode && !TargetMode.second.empty()) {
+      CommandLine.insert(++CommandLine.begin(), TargetMode.second);
+    }
+    if (!AlreadyHasTarget && !TargetMode.first.empty()) {
+      CommandLine.insert(++CommandLine.begin(), {"-target", TargetMode.first});
+    }
+  }
+}
+
 namespace {
 
 class SingleFrontendActionFactory : public FrontendActionFactory {
Index: unittests/Tooling/ToolingTest.cpp
===================================================================
--- unittests/Tooling/ToolingTest.cpp
+++ unittests/Tooling/ToolingTest.cpp
@@ -18,6 +18,8 @@
 #include "clang/Tooling/Tooling.h"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/Config/llvm-config.h"
+#include "llvm/Support/TargetSelect.h"
+#include "llvm/Support/TargetRegistry.h"
 #include "gtest/gtest.h"
 #include <algorithm>
 #include <string>
@@ -291,6 +293,84 @@
   EXPECT_FALSE(Found);
 }
 
+namespace {
+/// Find a target name such that looking for it in TargetRegistry by that name
+/// returns the same target. We expect that there is at least one target
+/// configured with this property.
+std::string getAnyTarget() {
+  llvm::InitializeAllTargets();
+  for (const auto &Target : llvm::TargetRegistry::targets()) {
+    std::string Error;
+    if (llvm::TargetRegistry::lookupTarget(Target.getName(), Error) ==
+        &Target) {
+      return Target.getName();
+    }
+  }
+  return "";
+}
+}
+
+TEST(addTargetAndModeForProgramName, AddsTargetAndMode) {
+  std::string Target = getAnyTarget();
+  ASSERT_FALSE(Target.empty());
+
+  std::vector<std::string> Args = {"clang", "-foo"};
+  addTargetAndModeForProgramName(Args, "");
+  EXPECT_EQ((std::vector<std::string>{"clang", "-foo"}), Args);
+  addTargetAndModeForProgramName(Args, Target + "-g++");
+  EXPECT_EQ((std::vector<std::string>{"clang", "-target", Target,
+                                      "--driver-mode=g++", "-foo"}),
+            Args);
+}
+
+TEST(addTargetAndModeForProgramName, PathIgnored) {
+  std::string Target = getAnyTarget();
+  ASSERT_FALSE(Target.empty());
+
+  SmallString<32> ToolPath;
+  llvm::sys::path::append(ToolPath, "foo", "bar", Target + "-g++");
+
+  std::vector<std::string> Args = {"clang", "-foo"};
+  addTargetAndModeForProgramName(Args, ToolPath);
+  EXPECT_EQ((std::vector<std::string>{"clang", "-target", Target,
+                                      "--driver-mode=g++", "-foo"}),
+            Args);
+}
+
+TEST(addTargetAndModeForProgramName, IgnoresExistingTarget) {
+  std::string Target = getAnyTarget();
+  ASSERT_FALSE(Target.empty());
+
+  std::vector<std::string> Args = {"clang", "-foo", "-target", "something"};
+  addTargetAndModeForProgramName(Args, Target + "-g++");
+  EXPECT_EQ((std::vector<std::string>{"clang", "--driver-mode=g++", "-foo",
+                                      "-target", "something"}),
+            Args);
+
+  std::vector<std::string> ArgsAlt = {"clang", "-foo", "-target=something"};
+  addTargetAndModeForProgramName(ArgsAlt, Target + "-g++");
+  EXPECT_EQ((std::vector<std::string>{"clang", "--driver-mode=g++", "-foo",
+                                      "-target=something"}),
+            ArgsAlt);
+}
+
+TEST(addTargetAndModeForProgramName, IgnoresExistingMode) {
+  std::string Target = getAnyTarget();
+  ASSERT_FALSE(Target.empty());
+
+  std::vector<std::string> Args = {"clang", "-foo", "--driver-mode=abc"};
+  addTargetAndModeForProgramName(Args, Target + "-g++");
+  EXPECT_EQ((std::vector<std::string>{"clang", "-target", Target, "-foo",
+                                      "--driver-mode=abc"}),
+            Args);
+
+  std::vector<std::string> ArgsAlt = {"clang", "-foo", "--driver-mode", "abc"};
+  addTargetAndModeForProgramName(ArgsAlt, Target + "-g++");
+  EXPECT_EQ((std::vector<std::string>{"clang", "-target", Target, "-foo",
+                                      "--driver-mode", "abc"}),
+            ArgsAlt);
+}
+
 #ifndef LLVM_ON_WIN32
 TEST(ClangToolTest, BuildASTs) {
   FixedCompilationDatabase Compilations("/", std::vector<std::string>());