[ThinLTO] Add Visibility bits to GlobalValueSummary::GVFlags

Imported functions and variable get the visibility from the module supplying the
definition.  However, non-imported definitions do not get the visibility from
(ELF) the most constraining visibility among all modules (Mach-O) the visibility
of the prevailing definition.

This patch

* adds visibility bits to GlobalValueSummary::GVFlags
* computes the result visibility and propagates it to all definitions

Protected/hidden can imply dso_local which can enable some optimizations (this
is stronger than GVFlags::DSOLocal because the implied dso_local can be
leveraged for ELF -shared while default visibility dso_local has to be cleared
for ELF -shared).

Note: we don't have summaries for declarations, so for ELF if a declaration has
the most constraining visibility, the result visibility may not be that one.

Differential Revision: https://reviews.llvm.org/D92900

1 files changed, 14 insertions, 0 deletions

diff --git a/llvm/lib/IR/ModuleSummaryIndex.cpp b/llvm/lib/IR/ModuleSummaryIndex.cpp
index 5d21ca7..df3e801 100644
--- a/llvm/lib/IR/ModuleSummaryIndex.cpp
+++ b/llvm/lib/IR/ModuleSummaryIndex.cpp
@@ -40,6 +40,18 @@ constexpr uint32_t FunctionSummary::ParamAccess::RangeWidth;
 FunctionSummary FunctionSummary::ExternalNode =
     FunctionSummary::makeDummyFunctionSummary({});
 
+GlobalValue::VisibilityTypes ValueInfo::getELFVisibility() const {
+  bool HasProtected = false;
+  for (const auto &S : make_pointee_range(getSummaryList())) {
+    if (S.getVisibility() == GlobalValue::HiddenVisibility)
+      return GlobalValue::HiddenVisibility;
+    if (S.getVisibility() == GlobalValue::ProtectedVisibility)
+      HasProtected = true;
+  }
+  return HasProtected ? GlobalValue::ProtectedVisibility
+                      : GlobalValue::DefaultVisibility;
+}
+
 bool ValueInfo::isDSOLocal() const {
   // Need to check all summaries are local in case of hash collisions.
   return getSummaryList().size() &&
@@ -564,6 +576,8 @@ void ModuleSummaryIndex::exportToDot(
         if (Flags.Live && hasConstantFlag(SummaryIt.second))
           A.addComment("constant");
       }
+      if (Flags.Visibility)
+        A.addComment("visibility");
       if (Flags.DSOLocal)
         A.addComment("dsoLocal");
       if (Flags.CanAutoHide)