Index: lib/LTO/LTO.cpp
===================================================================
--- lib/LTO/LTO.cpp
+++ lib/LTO/LTO.cpp
@@ -665,6 +665,15 @@
         auto GUID = GlobalValue::getGUID(GlobalValue::getGlobalIdentifier(
             Sym.getIRName(), GlobalValue::ExternalLinkage, ""));
         ThinLTO.PrevailingModuleForGUID[GUID] = BM.getModuleIdentifier();
+
+        // For linker redefined symbols (via --wrap or --defsym) we want to
+        // switch the linkage to `weak` to prevent IPOs from happening.
+        // Find the summary in the module for this very GV and record the new
+        // linkage so that we can switch it when we import the GV.
+        auto S = ThinLTO.CombinedIndex.findSummaryInModule(
+            GUID, BM.getModuleIdentifier());
+        if (S && Res.LinkerRedefined)
+          S->setLinkage(GlobalValue::WeakAnyLinkage);
       }
     }
   }
Index: lib/Transforms/IPO/FunctionImport.cpp
===================================================================
--- lib/Transforms/IPO/FunctionImport.cpp
+++ lib/Transforms/IPO/FunctionImport.cpp
@@ -537,7 +537,11 @@
   };
 
   auto updateLinkage = [&](GlobalValue &GV) {
-    if (!GlobalValue::isWeakForLinker(GV.getLinkage()))
+    // Only rename symbols that are weak for the linker, i.e.
+    // have linkonce or linkonce_odr linkage or have been explicitly
+    // redefined at link time, via, e.g. --wrap or -defsym (in ELF).
+    if (GV.getLinkage() == GlobalValue::AppendingLinkage ||
+        GV.getLinkage() == GlobalValue::ExternalLinkage)
       return;
     // See if the global summary analysis computed a new resolved linkage.
     const auto &GS = DefinedGlobals.find(GV.getGUID());
Index: test/LTO/Resolution/X86/linker-redef-thin.ll
===================================================================
--- /dev/null
+++ test/LTO/Resolution/X86/linker-redef-thin.ll
@@ -0,0 +1,16 @@
+; RUN: opt -module-summmary %s -o %t.o
+; RUN: llvm-lto2 run -o %t1.o %t.o -r %t.o,bar,pr
+; RUN: llvm-readobj -t %t1.o.0 | FileCheck %s
+
+; CHECK: Name: bar
+; CHECK-NEXT: Value:
+; CHECK-NEXT: Size:
+; CHECK-NEXT: Binding: Weak
+; CHECK-NEXT: Type: Function
+
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+define void @bar() {
+  ret void
+}