commit 769134dac3f1968495f7341882e6e7c719545ead
author Vitaly Buka <vitalybuka@google.com> Fri Feb 16 23:38:22 2018 +0000
committer Vitaly Buka <vitalybuka@google.com> Fri Feb 16 23:38:22 2018 +0000
tree efcbd618079ef6af5bbd465d08ad7233d81e19e7
parent c35ff824de59904ff7cc8c93620feacae7947c3b

[ThinLTO] Allow indexing to request backend to ignore the module

Summary:
Gold plugin does not add pass to ThinLTO modules without useful symbols.
In this case ThinLTO can't create corresponding index file and some features, like CFI,
cannot be processes by backed correctly without index.
Given that we don't need the backed output we can request it to avoid
processing the module. This is implemented by this patch using new
"SkipModuleByDistributedBackend" flag.

Reviewers: pcc, tejohnson

Subscribers: mehdi_amini, inglorion, eraman, cfe-commits

Differential Revision: https://reviews.llvm.org/D42995

llvm-svn: 325411

llvm/lib/Bitcode/Reader/BitcodeReader.cpp

diff --git a/llvm/lib/Bitcode/Reader/BitcodeReader.cpp b/llvm/lib/Bitcode/Reader/BitcodeReader.cpp
index a6e42b2..f38f7df 100644
--- a/llvm/lib/Bitcode/Reader/BitcodeReader.cpp
+++ b/llvm/lib/Bitcode/Reader/BitcodeReader.cpp
@@ -5186,11 +5186,14 @@
     case bitc::FS_FLAGS: {  // [flags]
       uint64_t Flags = Record[0];
       // Scan flags (set only on the combined index).
-      assert(Flags <= 1 && "Unexpected bits in flag");
+      assert(Flags <= 0x3 && "Unexpected bits in flag");
 
       // 1 bit: WithGlobalValueDeadStripping flag.
       if (Flags & 0x1)
         TheIndex.setWithGlobalValueDeadStripping();
+      // 1 bit: SkipModuleByDistributedBackend flag.
+      if (Flags & 0x2)
+        TheIndex.setSkipModuleByDistributedBackend();
       break;
     }
     case bitc::FS_VALUE_GUID: { // [valueid, refguid]

llvm/lib/Bitcode/Writer/BitcodeWriter.cpp

diff --git a/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp b/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp
index 5a473d6..15c06f5 100644
--- a/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp
+++ b/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp
@@ -3604,10 +3604,13 @@
   Stream.EnterSubblock(bitc::GLOBALVAL_SUMMARY_BLOCK_ID, 3);
   Stream.EmitRecord(bitc::FS_VERSION, ArrayRef<uint64_t>{INDEX_VERSION});
 
-  // Write the index flags. Currently we only write a single flag, the value of
-  // withGlobalValueDeadStripping, which only applies to the combined index.
-  Stream.EmitRecord(bitc::FS_FLAGS,
-                    ArrayRef<uint64_t>{Index.withGlobalValueDeadStripping()});
+  // Write the index flags.
+  uint64_t Flags = 0;
+  if (Index.withGlobalValueDeadStripping())
+    Flags |= 0x1;
+  if (Index.skipModuleByDistributedBackend())
+    Flags |= 0x2;
+  Stream.EmitRecord(bitc::FS_FLAGS, ArrayRef<uint64_t>{Flags});
 
   for (const auto &GVI : valueIds()) {
     Stream.EmitRecord(bitc::FS_VALUE_GUID,