[ThinLTO] Add an option to disable (thin)lto internalization.

Summary:
LTO and ThinLTO optimizes the IR differently.

One source of differences is the amount of internalizations that
can happen.

Add an option to enable/disable internalization so that other
differences can be studied in isolation. e.g. inlining.

There are other things lto and thinlto do differently, I will add
flags to enable/disable them as needed.

Reviewers: tejohnson, pcc, steven_wu

Subscribers: mehdi_amini, inglorion, steven_wu, dexonsmith, dang, llvm-commits

Differential Revision: https://reviews.llvm.org/D53294

llvm-svn: 346140

1 files changed, 8 insertions, 2 deletions

diff --git a/llvm/lib/LTO/LTO.cpp b/llvm/lib/LTO/LTO.cpp
index 6942cb2..2726b67 100644
--- a/llvm/lib/LTO/LTO.cpp
+++ b/llvm/lib/LTO/LTO.cpp
@@ -56,6 +56,11 @@ static cl::opt<bool>
     DumpThinCGSCCs("dump-thin-cg-sccs", cl::init(false), cl::Hidden,
                    cl::desc("Dump the SCCs in the ThinLTO index's callgraph"));
 
+/// Enable global value internalization in LTO.
+cl::opt<bool> EnableLTOInternalization(
+    "enable-lto-internalization", cl::init(true), cl::Hidden,
+    cl::desc("Enable global value internalization in LTO"));
+
 // Returns a unique hash for the Module considering the current list of
 // export/import and other global analysis results.
 // The hash is produced in \p Key.
@@ -344,7 +349,8 @@ static void thinLTOInternalizeAndPromoteGUID(
     if (isExported(S->modulePath(), GUID)) {
       if (GlobalValue::isLocalLinkage(S->linkage()))
         S->setLinkage(GlobalValue::ExternalLinkage);
-    } else if (!GlobalValue::isLocalLinkage(S->linkage()))
+    } else if (EnableLTOInternalization &&
+               !GlobalValue::isLocalLinkage(S->linkage()))
       S->setLinkage(GlobalValue::InternalLinkage);
   }
 }
@@ -876,7 +882,7 @@ Error LTO::runRegularLTO(AddStreamFn AddStream) {
         continue;
       GV->setUnnamedAddr(R.second.UnnamedAddr ? GlobalValue::UnnamedAddr::Global
                                               : GlobalValue::UnnamedAddr::None);
-      if (R.second.Partition == 0)
+      if (EnableLTOInternalization && R.second.Partition == 0)
         GV->setLinkage(GlobalValue::InternalLinkage);
     }