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

diff --git a/lib/Transforms/IPO/FunctionImport.cpp b/lib/Transforms/IPO/FunctionImport.cpp
index da763b18d4d461b6e7897ab90a0799a04f8afab3..b043687f898925ba8c96a519ecd57309a4ed3040 100644 (file)
--- a/lib/Transforms/IPO/FunctionImport.cpp
+++ b/lib/Transforms/IPO/FunctionImport.cpp
@@ -488,17 +488,14 @@ void llvm::computeDeadSymbols(
   while (!Worklist.empty()) {
     auto VI = Worklist.pop_back_val();
     for (auto &Summary : VI.getSummaryList()) {
-      for (auto Ref : Summary->refs())
+      GlobalValueSummary *Base = Summary.get();
+      if (auto *AS = dyn_cast<AliasSummary>(Base))
+        Base = &AS->getAliasee();
+      for (auto Ref : Base->refs())
         visit(Ref);
-      if (auto *FS = dyn_cast<FunctionSummary>(Summary.get()))
+      if (auto *FS = dyn_cast<FunctionSummary>(Base))
         for (auto Call : FS->calls())
           visit(Call.first);
-      if (auto *AS = dyn_cast<AliasSummary>(Summary.get())) {
-        auto AliaseeGUID = AS->getAliasee().getOriginalName();
-        ValueInfo AliaseeVI = Index.getValueInfo(AliaseeGUID);
-        if (AliaseeVI)
-          visit(AliaseeVI);
-      }
     }
   }
   Index.setWithGlobalValueDeadStripping();

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 (file)
index 0000000..16154d2
--- /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 (file)
index 0000000..d009a48
--- /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
+}