ThinLTO: Correctly follow aliasee references when dead stripping.

We were previously handling aliases during dead stripping by adding
the aliased global's "original name" GUID to the worklist. This will
lead to incorrect behaviour if the global has local linkage because
the original name GUID will not correspond to the global's GUID in
the summary.

Because an alias is just another name for the global that it
references, there is no need to mark the referenced global as used,
or to follow references from any other copies of the global. So all
we need to do is to follow references from the aliasee's summary
instead of the alias.

Differential Revision: https://reviews.llvm.org/D37789

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@313157 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 24 insertions, 0 deletions

diff --git a/test/LTO/Resolution/X86/Inputs/dead-strip-alias.ll b/test/LTO/Resolution/X86/Inputs/dead-strip-alias.ll
new file mode 100644
index 00000000000..16154d2c45b
--- /dev/null
+++ b/test/LTO/Resolution/X86/Inputs/dead-strip-alias.ll
@@ -0,0 +1,4 @@
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+@external = global i8 42
diff --git a/test/LTO/Resolution/X86/dead-strip-alias.ll b/test/LTO/Resolution/X86/dead-strip-alias.ll
new file mode 100644
index 00000000000..d009a484e4f
--- /dev/null
+++ b/test/LTO/Resolution/X86/dead-strip-alias.ll
@@ -0,0 +1,20 @@
+; RUN: opt -module-summary -o %t %s
+; RUN: opt -module-summary -o %t2 %S/Inputs/dead-strip-alias.ll
+; RUN: llvm-lto2 run %t -r %t,main,px -r %t,alias,p -r %t,external, \
+; RUN:               %t2 -r %t2,external,p \
+; RUN: -save-temps -o %t3
+; RUN: llvm-nm %t3.1 | FileCheck %s
+
+; CHECK: D external
+
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+@alias = alias i8*, i8** @internal
+
+@internal = internal global i8* @external
+@external = external global i8
+
+define i8** @main() {
+  ret i8** @alias
+}