[LLD][ThinLTO] Handle GUID collision in import global processing

Summary:
If there are a GUID collision between two globals checking the
summarylist from the import index to make assumption can be dangerous.

Do not assume that a GlobalValue that has a GlobalVarSummary
actually is a GlobalVariable as it can be another GlobalValue with
the same GUID that the summary is connected to.

Patch by Joel Klinghed (the_jk@opera.com)

Reviewers: evgeny777, tejohnson

Reviewed By: tejohnson

Subscribers: tejohnson, dblaikie, MaskRay, mehdi_amini, inglorion, hiraditya, steven_wu, dexonsmith, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D67322

1 files changed, 11 insertions, 5 deletions

diff --git a/llvm/lib/Transforms/Utils/FunctionImportUtils.cpp b/llvm/lib/Transforms/Utils/FunctionImportUtils.cpp
index 76b4635ad50..3109224dc2c 100644
--- a/llvm/lib/Transforms/Utils/FunctionImportUtils.cpp
+++ b/llvm/lib/Transforms/Utils/FunctionImportUtils.cpp
@@ -239,11 +239,17 @@ void FunctionImportGlobalProcessing::processGlobalForThinLTO(GlobalValue &GV) {
   // propagateConstants hasn't been run. We can't internalize GV
   // in such case.
   if (!GV.isDeclaration() && VI && ImportIndex.withGlobalValueDeadStripping()) {
-    const auto &SL = VI.getSummaryList();
-    auto *GVS = SL.empty() ? nullptr : dyn_cast<GlobalVarSummary>(SL[0].get());
-    // At this stage "maybe" is "definitely"
-    if (GVS && (GVS->maybeReadOnly() || GVS->maybeWriteOnly()))
-      cast<GlobalVariable>(&GV)->addAttribute("thinlto-internalize");
+    if (GlobalVariable *V = dyn_cast<GlobalVariable>(&GV)) {
+      // We can have more than one local with the same GUID, in the case of
+      // same-named locals in different but same-named source files that were
+      // compiled in their respective directories (so the source file name
+      // and resulting GUID is the same). Find the one in this module.
+      auto* GVS = dyn_cast<GlobalVarSummary>(
+          ImportIndex.findSummaryInModule(VI, M.getModuleIdentifier()));
+      // At this stage "maybe" is "definitely"
+      if (GVS && (GVS->maybeReadOnly() || GVS->maybeWriteOnly()))
+        V->addAttribute("thinlto-internalize");
+    }
   }
 
   bool DoPromote = false;