[ThinLTO] Scan all variants of vague symbol for reachability.

Summary:
Alias can make one (but not all) live, we still need to scan all others if this symbol is reachable
from somewhere else.

Reviewers: tejohnson, grimar

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

Differential Revision: https://reviews.llvm.org/D56117

llvm-svn: 350269

1 files changed, 8 insertions, 3 deletions

diff --git a/llvm/lib/Transforms/IPO/FunctionImport.cpp b/llvm/lib/Transforms/IPO/FunctionImport.cpp
index 531a7c19e36..1223a23512e 100644
--- a/llvm/lib/Transforms/IPO/FunctionImport.cpp
+++ b/llvm/lib/Transforms/IPO/FunctionImport.cpp
@@ -777,9 +777,14 @@ void llvm::computeDeadSymbols(
     VI = updateValueInfoForIndirectCalls(Index, VI);
     if (!VI)
       return;
-    for (auto &S : VI.getSummaryList())
-      if (S->isLive())
-        return;
+
+    // We need to make sure all variants of the symbol are scanned, alias can
+    // make one (but not all) alive.
+    if (llvm::all_of(VI.getSummaryList(),
+                     [](const std::unique_ptr<llvm::GlobalValueSummary> &S) {
+                       return S->isLive();
+                     }))
+      return;
 
     // We only keep live symbols that are known to be non-prevailing if any are
     // available_externally, linkonceodr, weakodr. Those symbols are discarded