From 3dd728914163cdf3ed9c4e16f99a441721077f4b Mon Sep 17 00:00:00 2001
From: Fangrui Song <i@maskray.me>
Date: Thu, 31 Oct 2019 22:31:03 -0700
Subject: [PATCH] Infer -target and --driver-mode from argv[0]

Fix #511
---
 src/clang_tu.cc | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/src/clang_tu.cc b/src/clang_tu.cc
index b153a8e0..ee99c4d6 100644
--- a/src/clang_tu.cc
+++ b/src/clang_tu.cc
@@ -7,6 +7,7 @@
 #include "platform.hh"
 
 #include <clang/AST/Type.h>
+#include <clang/Driver/Driver.h>
 #include <clang/Lex/Lexer.h>
 #include <llvm/Support/Path.h>
 
@@ -79,6 +80,19 @@ buildCompilerInvocation(const std::string &main, std::vector<const char *> args,
   IntrusiveRefCntPtr<DiagnosticsEngine> diags(
       CompilerInstance::createDiagnostics(new DiagnosticOptions,
                                           new IgnoringDiagConsumer, true));
+
+  // Similar to clang/tools/driver/driver.cpp:insertTargetAndModeArgs but don't
+  // require llvm::InitializeAllTargetInfos().
+  driver::Driver d(args[0], llvm::sys::getDefaultTargetTriple(), *diags);
+  auto target_and_mode =
+      driver::ToolChain::getTargetAndModeFromProgramName(args[0]);
+  if (target_and_mode.DriverMode)
+    args.insert(args.begin() + 1, target_and_mode.DriverMode);
+  if (!target_and_mode.TargetPrefix.empty()) {
+    const char *arr[] = {"-target", target_and_mode.TargetPrefix.c_str()};
+    args.insert(args.begin() + 1, std::begin(arr), std::end(arr));
+  }
+
   std::unique_ptr<CompilerInvocation> ci =
       createInvocationFromCommandLine(args, diags, vfs);
   if (ci) {