[ThinLTO] Fix printing of aliases for distributed backend indexes

Summary:
When we import an alias (which will import a copy of the aliasee), but
aren't going to import the aliasee directly, the distributed backend
index will not contain the aliasee summary. Handle this in the summary
assembly printer by printing "null" as the aliasee.

Reviewers: davidxl, dexonsmith

Subscribers: mehdi_amini, inglorion, eraman, steven_wu, llvm-commits

Differential Revision: https://reviews.llvm.org/D48699

llvm-svn: 336160

Author: teresajohnson

llvm/lib/IR/AsmWriter.cpp

@@ -2788,8 +2788,14 @@ static const char *getSummaryKindName(GlobalValueSummary::SummaryKind SK) {
 }
 
 void AssemblyWriter::printAliasSummary(const AliasSummary *AS) {
-  Out << ", aliasee: ^"
-      << Machine.getGUIDSlot(SummaryToGUIDMap[&AS->getAliasee()]);
+  Out << ", aliasee: ";
+  // The indexes emitted for distributed backends may not include the
+  // aliasee summary (only if it is being imported directly). Handle
+  // that case by just emitting "null" as the aliasee.
+  if (AS->hasAliasee())
+    Out << "^" << Machine.getGUIDSlot(SummaryToGUIDMap[&AS->getAliasee()]);
+  else
+    Out << "null";
 }
 
 void AssemblyWriter::printGlobalVarSummary(const GlobalVarSummary *GS) {

llvm/test/ThinLTO/X86/distributed_indexes.ll

@@ -40,6 +40,12 @@
 ; BACKEND2-NEXT: <COMBINED_ALIAS
 ; BACKEND2-NEXT: </GLOBALVAL_SUMMARY_BLOCK
 
+; Make sure that when the alias is imported as a copy of the aliasee, but the
+; aliasee is not being imported by itself, that we can still print the summary.
+; The aliasee should be "null".
+; RUN: llvm-dis %t1.bc.thinlto.bc -o - | FileCheck %s --check-prefix=DIS
+; DIS: aliasee: null
+
 declare void @g(...)
 declare void @analias(...)