[ThinLTO] Enable importing of aliases as copy of aliasee

Summary:
This implements a missing feature to allow importing of aliases, which
was previously disabled because alias cannot be available_externally.
We instead import an alias as a copy of its aliasee.

Some additional work was required in the IndexBitcodeWriter for the
distributed build case, to ensure that the aliasee has a value id
in the distributed index file (i.e. even when it is not being
imported directly).

This is a performance win in codes that have many aliases, e.g. C++
applications that have many constructor and destructor aliases.

Reviewers: pcc

Subscribers: mehdi_amini, inglorion, eraman, llvm-commits

Differential Revision: https://reviews.llvm.org/D40747

llvm-svn: 320895

1 files changed, 2 insertions, 2 deletions

diff --git a/llvm/lib/Bitcode/Reader/BitcodeReader.cpp b/llvm/lib/Bitcode/Reader/BitcodeReader.cpp
index eafe911ed87..95291a1caf9 100644
--- a/llvm/lib/Bitcode/Reader/BitcodeReader.cpp
+++ b/llvm/lib/Bitcode/Reader/BitcodeReader.cpp
@@ -5202,6 +5202,7 @@ Error ModuleSummaryIndexBitcodeReader::parseEntireSummary(unsigned ID) {
       if (!AliaseeInModule)
         return error("Alias expects aliasee summary to be parsed");
       AS->setAliasee(AliaseeInModule);
+      AS->setAliaseeGUID(AliaseeGUID);
 
       auto GUID = getValueInfoFromValueId(ValueID);
       AS->setOriginalName(GUID.second);
@@ -5288,9 +5289,8 @@ Error ModuleSummaryIndexBitcodeReader::parseEntireSummary(unsigned ID) {
           getValueInfoFromValueId(AliaseeValueId).first.getGUID();
       auto AliaseeInModule =
           TheIndex.findSummaryInModule(AliaseeGUID, AS->modulePath());
-      if (!AliaseeInModule)
-        return error("Alias expects aliasee summary to be parsed");
       AS->setAliasee(AliaseeInModule);
+      AS->setAliaseeGUID(AliaseeGUID);
 
       ValueInfo VI = getValueInfoFromValueId(ValueID).first;
       LastSeenGUID = VI.getGUID();