diff --git a/src/clang_tu.cc b/src/clang_tu.cc
index 8fb8403f..f7fb6d0f 100644
--- a/src/clang_tu.cc
+++ b/src/clang_tu.cc
@@ -81,7 +81,7 @@ Range FromTokenRangeDefaulted(const SourceManager &SM, const LangOptions &Lang,
 }
 
 std::unique_ptr<CompilerInvocation>
-BuildCompilerInvocation(std::vector<const char *> args,
+BuildCompilerInvocation(const std::string &main, std::vector<const char *> args,
                         IntrusiveRefCntPtr<llvm::vfs::FileSystem> VFS) {
   std::string save = "-resource-dir=" + g_config->clang.resourceDir;
   args.push_back(save.c_str());
@@ -94,6 +94,9 @@ BuildCompilerInvocation(std::vector<const char *> args,
     CI->getDiagnosticOpts().IgnoreWarnings = true;
     CI->getFrontendOpts().DisableFree = false;
     CI->getLangOpts()->SpellChecking = false;
+    auto &IS = CI->getFrontendOpts().Inputs;
+    if (IS.size())
+      IS[0] = FrontendInputFile(main, IS[0].getKind(), IS[0].isSystem());
   }
   return CI;
 }
diff --git a/src/clang_tu.hh b/src/clang_tu.hh
index f301334f..4adc4632 100644
--- a/src/clang_tu.hh
+++ b/src/clang_tu.hh
@@ -39,7 +39,8 @@ Range FromTokenRangeDefaulted(const clang::SourceManager &SM,
                               Range range);
 
 std::unique_ptr<clang::CompilerInvocation>
-BuildCompilerInvocation(std::vector<const char *> args,
+BuildCompilerInvocation(const std::string &main,
+                        std::vector<const char *> args,
                         llvm::IntrusiveRefCntPtr<llvm::vfs::FileSystem> VFS);
 
 const char *ClangBuiltinTypeName(int);
diff --git a/src/indexer.cc b/src/indexer.cc
index d33299dc..d8631692 100644
--- a/src/indexer.cc
+++ b/src/indexer.cc
@@ -1217,14 +1217,15 @@ void Init() {
 
 std::vector<std::unique_ptr<IndexFile>>
 Index(SemaManager *manager, WorkingFiles *wfiles, VFS *vfs,
-      const std::string &opt_wdir, const std::string &file,
+      const std::string &opt_wdir, const std::string &main,
       const std::vector<const char *> &args,
       const std::vector<std::pair<std::string, std::string>> &remapped,
       bool &ok) {
   ok = true;
   auto PCH = std::make_shared<PCHContainerOperations>();
   llvm::IntrusiveRefCntPtr<llvm::vfs::FileSystem> FS = llvm::vfs::getRealFileSystem();
-  std::shared_ptr<CompilerInvocation> CI = BuildCompilerInvocation(args, FS);
+  std::shared_ptr<CompilerInvocation> CI =
+      BuildCompilerInvocation(main, args, FS);
   // e.g. .s
   if (!CI)
     return {};
@@ -1234,35 +1235,13 @@ Index(SemaManager *manager, WorkingFiles *wfiles, VFS *vfs,
   CI->getLangOpts()->CommentOpts.ParseAllComments =
       g_config->index.comments > 1;
   CI->getLangOpts()->RetainCommentsFromSystemHeaders = true;
-  std::string buf = wfiles->GetContent(file);
+  std::string buf = wfiles->GetContent(main);
   std::vector<std::unique_ptr<llvm::MemoryBuffer>> Bufs;
-  if (buf.size()) {
-    // If there is a completion session, reuse its preamble if exists.
-    bool done_remap = false;
-#if 0
-    std::shared_ptr<CompletionSession> session =
-      manager->TryGetSession(file, false, false);
-    if (session)
-      if (auto preamble = session->GetPreamble()) {
-        Bufs.push_back(llvm::MemoryBuffer::getMemBuffer(buf));
-        auto Bounds = ComputePreambleBounds(*CI->getLangOpts(), Bufs.back().get(), 0);
-        if (preamble->Preamble.CanReuse(*CI, Bufs.back().get(), Bounds,
-                                        FS.get())) {
-          preamble->Preamble.AddImplicitPreamble(*CI, FS, Bufs.back().get());
-          done_remap = true;
-        }
-      }
-#endif
+  if (buf.size())
     for (auto &[filename, content] : remapped) {
-      if (filename == file && done_remap)
-        continue;
       Bufs.push_back(llvm::MemoryBuffer::getMemBuffer(content));
-      CI->getPreprocessorOpts().addRemappedFile(
-          filename == file ? CI->getFrontendOpts().Inputs[0].getFile()
-                           : StringRef(filename),
-          Bufs.back().get());
+      CI->getPreprocessorOpts().addRemappedFile(filename, Bufs.back().get());
     }
-  }
 
   DiagnosticConsumer DC;
   auto Clang = std::make_unique<CompilerInstance>(PCH);
@@ -1291,20 +1270,20 @@ Index(SemaManager *manager, WorkingFiles *wfiles, VFS *vfs,
   {
     llvm::CrashRecoveryContext CRC;
     auto parse = [&]() {
-                   if (!Action->BeginSourceFile(*Clang, Clang->getFrontendOpts().Inputs[0]))
-                     return;
-                   if (!Action->Execute())
-                     return;
-                   Action->EndSourceFile();
-                   ok = true;
-                 };
+      if (!Action->BeginSourceFile(*Clang, Clang->getFrontendOpts().Inputs[0]))
+        return;
+      if (!Action->Execute())
+        return;
+      Action->EndSourceFile();
+      ok = true;
+    };
     if (!CRC.RunSafely(parse)) {
-      LOG_S(ERROR) << "clang crashed for " << file;
+      LOG_S(ERROR) << "clang crashed for " << main;
       return {};
     }
   }
   if (!ok) {
-    LOG_S(ERROR) << "failed to index " << file;
+    LOG_S(ERROR) << "failed to index " << main;
     return {};
   }
   for (auto &Buf : Bufs)
@@ -1315,7 +1294,7 @@ Index(SemaManager *manager, WorkingFiles *wfiles, VFS *vfs,
     if (!it.second.db)
       continue;
     std::unique_ptr<IndexFile> &entry = it.second.db;
-    entry->import_file = file;
+    entry->import_file = main;
     entry->args = args;
     for (auto &[_, it] : entry->uid2lid_and_path)
       entry->lid2path.emplace_back(it.first, std::move(it.second));
diff --git a/src/pipeline.cc b/src/pipeline.cc
index c7b8e204..d4a3f788 100644
--- a/src/pipeline.cc
+++ b/src/pipeline.cc
@@ -17,6 +17,7 @@
 #include <rapidjson/document.h>
 #include <rapidjson/writer.h>
 
+#include <llvm/Support/Path.h>
 #include <llvm/Support/Process.h>
 #include <llvm/Support/Threading.h>
 using namespace llvm;
@@ -110,9 +111,11 @@ bool CacheInvalid(VFS *vfs, IndexFile *prev, const std::string &path,
     }
   }
 
+  // For inferred files, allow -o a a.cc -> -o b b.cc
+  std::string stem = sys::path::stem(path);
   bool changed = prev->args.size() != args.size();
   for (size_t i = 0; !changed && i < args.size(); i++)
-    if (strcmp(prev->args[i], args[i]))
+    if (strcmp(prev->args[i], args[i]) && sys::path::stem(args[i]) != stem)
       changed = true;
   if (changed)
     LOG_S(INFO) << "args changed for " << path
@@ -195,7 +198,8 @@ bool Indexer_Parse(SemaManager *completion, WorkingFiles *wfiles,
   }
 
   // must_exist is currently unused.
-  Project::Entry entry = project->FindEntry(request.path, false);
+  Project::Entry entry =
+      project->FindEntry(request.path, true, request.must_exist);
   if (request.must_exist && entry.filename.empty())
     return true;
   if (request.args.size())
diff --git a/src/project.cc b/src/project.cc
index b4347174..c96eac1e 100644
--- a/src/project.cc
+++ b/src/project.cc
@@ -411,17 +411,24 @@ void Project::Load(const std::string &root) {
   }
 }
 
-Project::Entry Project::FindEntry(const std::string &path,
+Project::Entry Project::FindEntry(const std::string &path, bool can_redirect,
                                   bool must_exist) {
   Project::Folder *best_folder = nullptr;
   const Entry *best = nullptr;
   std::lock_guard lock(mtx);
   for (auto &[root, folder] : root2folder) {
+    // The entry may have different filename but it doesn't matter when building
+    // CompilerInvocation. The main filename is specified separately.
     auto it = folder.path2entry_index.find(path);
     if (it != folder.path2entry_index.end()) {
       Project::Entry &entry = folder.entries[it->second];
-      if (!must_exist || entry.filename == path)
+      if (can_redirect || entry.filename == path)
         return entry;
+      if (entry.compdb_size) {
+        best_folder = &folder;
+        best = &entry;
+      }
+      break;
     }
   }
 
@@ -471,7 +478,7 @@ out:
             best_folder = &folder;
           }
         }
-      }
+    }
   }
 
   ret.is_inferred = true;
@@ -485,14 +492,6 @@ out:
     ret.root = best->root;
     ret.directory = best->directory;
     ret.args = best->args;
-    std::string base_name = sys::path::filename(best->filename);
-    for (const char *&arg : ret.args) {
-      try {
-        if (arg == best->filename || sys::path::filename(arg) == base_name)
-          arg = Intern(path);
-      } catch (...) {
-      }
-    }
     ret.args.resize(best->compdb_size);
     if (extra && extra->size())
       ret.args.insert(ret.args.end(), extra->begin() + 1, extra->end());
diff --git a/src/project.hh b/src/project.hh
index 0434f402..472cb32a 100644
--- a/src/project.hh
+++ b/src/project.hh
@@ -56,7 +56,7 @@ struct Project {
 
   // Lookup the CompilationEntry for |filename|. If no entry was found this
   // will infer one based on existing project structure.
-  Entry FindEntry(const std::string &path, bool can_be_inferred);
+  Entry FindEntry(const std::string &path, bool can_redirect, bool must_exist);
 
   // If the client has overridden the flags, or specified them for a file
   // that is not in the compilation_database.json make sure those changes
diff --git a/src/sema_manager.cc b/src/sema_manager.cc
index 006c82be..afbc3a6f 100644
--- a/src/sema_manager.cc
+++ b/src/sema_manager.cc
@@ -409,7 +409,7 @@ void *PreambleMain(void *manager_) {
     IntrusiveRefCntPtr<llvm::vfs::FileSystem> FS =
         stat_cache->Producer(session->FS);
     if (std::unique_ptr<CompilerInvocation> CI =
-            BuildCompilerInvocation(session->file.args, FS))
+            BuildCompilerInvocation(task.path, session->file.args, FS))
       BuildPreamble(*session, *CI, FS, task, std::move(stat_cache));
 
     if (task.from_diag) {
@@ -449,7 +449,7 @@ void *CompletionMain(void *manager_) {
     IntrusiveRefCntPtr<llvm::vfs::FileSystem> FS =
         preamble ? preamble->stat_cache->Consumer(session->FS) : session->FS;
     std::unique_ptr<CompilerInvocation> CI =
-        BuildCompilerInvocation(session->file.args, FS);
+        BuildCompilerInvocation(task->path, session->file.args, FS);
     if (!CI)
       continue;
     auto &FOpts = CI->getFrontendOpts();
@@ -551,7 +551,7 @@ void *DiagnosticMain(void *manager_) {
     }
 
     std::unique_ptr<CompilerInvocation> CI =
-        BuildCompilerInvocation(session->file.args, FS);
+        BuildCompilerInvocation(task.path, session->file.args, FS);
     if (!CI)
       continue;
     // If main file is a header, add -Wno-unused-function
@@ -696,7 +696,7 @@ SemaManager::EnsureSession(const std::string &path, bool *created) {
   std::shared_ptr<ccls::Session> session = sessions.Get(path);
   if (!session) {
     session = std::make_shared<ccls::Session>(
-        project_->FindEntry(path, true), wfiles, PCH);
+        project_->FindEntry(path, false, false), wfiles, PCH);
     std::string line;
     if (LOG_V_ENABLED(1)) {
       line = "\n ";