[PATCH] D42995: [ThinLTO] Allow indexing to request backend to ignore the module

[Vitaly Buka via Phabricator via cfe-commits]

This revision was automatically updated to reflect the committed changes.
Closed by commit rC325411: [ThinLTO] Allow indexing to request backend to ignore the module (authored by vitalybuka, committed by ).

Changed prior to commit:
  https://reviews.llvm.org/D42995?vs=134657&id=134755#toc

Repository:
  rC Clang

https://reviews.llvm.org/D42995

Files:
  lib/CodeGen/BackendUtil.cpp
  test/CodeGen/Inputs/thinlto-distributed-backend-skip.bc
  test/CodeGen/thinlto-distributed-backend-skip.ll


Index: test/CodeGen/thinlto-distributed-backend-skip.ll
===================================================================
--- test/CodeGen/thinlto-distributed-backend-skip.ll
+++ test/CodeGen/thinlto-distributed-backend-skip.ll
@@ -0,0 +1,21 @@
+; REQUIRES: x86-registered-target
+
+; Check that ThinLTO backend respects "SkipModuleByDistributedBackend"
+; flag which can be set by indexing.
+
+; RUN: opt -thinlto-bc -o %t.o %s
+
+; RUN: %clang_cc1 -triple x86_64-grtev4-linux-gnu \
+; RUN:   -fthinlto-index=%S/Inputs/thinlto-distributed-backend-skip.bc \
+; RUN:   -emit-llvm -o - -x ir %t.o | FileCheck %s
+
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-grtev4-linux-gnu"
+
+; CHECK: "empty"
+; CHECK: target triple =
+; CHECK-NOT: @main
+define i32 @main() {
+entry:
+  ret i32 0
+}
Index: lib/CodeGen/BackendUtil.cpp
===================================================================
--- lib/CodeGen/BackendUtil.cpp
+++ lib/CodeGen/BackendUtil.cpp
@@ -1153,6 +1153,7 @@
                               const llvm::DataLayout &TDesc, Module *M,
                               BackendAction Action,
                               std::unique_ptr<raw_pwrite_stream> OS) {
+  std::unique_ptr<llvm::Module> EmptyModule;
   if (!CGOpts.ThinLTOIndexFile.empty()) {
     // If we are performing a ThinLTO importing compile, load the function index
     // into memory and pass it into runThinLTOBackend, which will run the
@@ -1170,11 +1171,22 @@
     // A null CombinedIndex means we should skip ThinLTO compilation
     // (LLVM will optionally ignore empty index files, returning null instead
     // of an error).
-    bool DoThinLTOBackend = CombinedIndex != nullptr;
-    if (DoThinLTOBackend) {
-      runThinLTOBackend(CombinedIndex.get(), M, HeaderOpts, CGOpts, TOpts,
-                        LOpts, std::move(OS), CGOpts.SampleProfileFile, Action);
-      return;
+    if (CombinedIndex) {
+      if (!CombinedIndex->skipModuleByDistributedBackend()) {
+        runThinLTOBackend(CombinedIndex.get(), M, HeaderOpts, CGOpts, TOpts,
+                          LOpts, std::move(OS), CGOpts.SampleProfileFile,
+                          Action);
+        return;
+      }
+      // Distributed indexing detected that nothing from the module is needed
+      // for the final linking. So we can skip the compilation. We sill need to
+      // output an empty object file to make sure that a linker does not fail
+      // trying to read it. Also for some features, like CFI, we must skip
+      // the compilation as CombinedIndex does not contain all required
+      // information.
+      EmptyModule = llvm::make_unique<llvm::Module>("empty", M->getContext());
+      EmptyModule->setTargetTriple(M->getTargetTriple());
+      M = EmptyModule.get();
     }
   }
 


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