Index: clangd/ClangdUnit.cpp
===================================================================
--- clangd/ClangdUnit.cpp
+++ clangd/ClangdUnit.cpp
@@ -529,12 +529,22 @@
       IntrusiveRefCntPtr<DiagnosticsEngine> PreambleDiagsEngine =
           CompilerInstance::createDiagnostics(
               &CI->getDiagnosticOpts(), &PreambleDiagnosticsConsumer, false);
+
+      // Skip function bodies when building the preamble to speed up building
+      // the preamble and make it smaller. CI is later reused to build the AST,
+      // so we set SkipFunctionBodies back to false after preamble is built.
+      assert(!CI->getFrontendOpts().SkipFunctionBodies);
+      CI->getFrontendOpts().SkipFunctionBodies = true;
+
       CppFilePreambleCallbacks SerializedDeclsCollector;
       auto BuiltPreamble = PrecompiledPreamble::Build(
           *CI, ContentsBuffer.get(), Bounds, *PreambleDiagsEngine, VFS, PCHs,
           /*StoreInMemory=*/That->StorePreamblesInMemory,
           SerializedDeclsCollector);
 
+      // Preamble is built, restore SkipFunctionBodies.
+      CI->getFrontendOpts().SkipFunctionBodies = false;
+
       if (BuiltPreamble) {
         log(Ctx, "Built preamble of size " + Twine(BuiltPreamble->getSize()) +
                      " for file " + Twine(That->FileName));