diff --git a/lld/MachO/Driver.cpp b/lld/MachO/Driver.cpp
--- a/lld/MachO/Driver.cpp
+++ b/lld/MachO/Driver.cpp
@@ -1472,14 +1472,15 @@
 
     gatherInputSections();
 
-    if (config->deadStrip)
-      markLive();
-
     // ICF assumes that all literals have been folded already, so we must run
     // foldIdenticalLiterals before foldIdenticalSections.
     foldIdenticalLiterals();
     if (config->icfLevel != ICFLevel::none)
       foldIdenticalSections();
+    registerCompactUnwindSections();
+
+    if (config->deadStrip)
+      markLive();
 
     // Write to an output file.
     if (target->wordSize == 8)
diff --git a/lld/MachO/InputFiles.h b/lld/MachO/InputFiles.h
--- a/lld/MachO/InputFiles.h
+++ b/lld/MachO/InputFiles.h
@@ -105,6 +105,7 @@
   const uint32_t modTime;
   std::vector<ConcatInputSection *> debugSections;
   ArrayRef<llvm::MachO::data_in_code_entry> dataInCodeEntries;
+  void registerCompactUnwind();
 
 private:
   template <class LP> void parse();
@@ -120,7 +121,9 @@
                         SubsectionMap &);
   void parseDebugInfo();
   void parseDataInCode();
-  void registerCompactUnwind();
+
+  // FIXME: not thread-safe?
+  bool doneCUReg = false;
 };
 
 // command-line -sectcreate file
@@ -212,6 +215,8 @@
 
 extern llvm::SetVector<InputFile *> inputFiles;
 
+void registerCompactUnwindSections();
+
 llvm::Optional<MemoryBufferRef> readFile(StringRef path);
 
 namespace detail {
diff --git a/lld/MachO/InputFiles.cpp b/lld/MachO/InputFiles.cpp
--- a/lld/MachO/InputFiles.cpp
+++ b/lld/MachO/InputFiles.cpp
@@ -65,6 +65,7 @@
 #include "llvm/LTO/LTO.h"
 #include "llvm/Support/Endian.h"
 #include "llvm/Support/MemoryBuffer.h"
+#include "llvm/Support/Parallel.h"
 #include "llvm/Support/Path.h"
 #include "llvm/Support/TarWriter.h"
 #include "llvm/TextAPI/Architecture.h"
@@ -93,6 +94,7 @@
 }
 
 SetVector<InputFile *> macho::inputFiles;
+
 std::unique_ptr<TarWriter> macho::tar;
 int InputFile::idCount = 0;
 
@@ -173,6 +175,14 @@
   return true;
 }
 
+void macho::registerCompactUnwindSections() {
+  parallelForEach(inputFiles, [](InputFile *file) {
+    if (ObjFile *objFile = dyn_cast_or_null<ObjFile>(file)) {
+      objFile->registerCompactUnwind();
+    }
+  });
+}
+
 // Open a given file path and return it as a memory-mapped file.
 Optional<MemoryBufferRef> macho::readFile(StringRef path) {
   ErrorOr<std::unique_ptr<MemoryBuffer>> mbOrErr = MemoryBuffer::getFile(path);
@@ -832,7 +842,6 @@
   parseDebugInfo();
   if (config->emitDataInCodeInfo)
     parseDataInCode();
-  registerCompactUnwind();
 }
 
 void ObjFile::parseDebugInfo() {
@@ -875,6 +884,7 @@
 
 // Create pointers from symbols to their associated compact unwind entries.
 void ObjFile::registerCompactUnwind() {
+  assert(!doneCUReg);
   // First, locate the __compact_unwind section.
   SubsectionMap *cuSubsecMap = nullptr;
   for (SubsectionMap &map : subsections) {
@@ -914,12 +924,14 @@
       // The relocation should point at the exact address of a symbol (with no
       // addend).
       if (it == referentIsec->symbols.end() || (*it)->value != add) {
-        assert(referentIsec->wasCoalesced);
+        assert(config->icfLevel == ICFLevel::none ||
+               referentIsec->wasCoalesced);
         continue;
       }
       (*it)->compactUnwind = isec;
     }
   }
+  doneCUReg = true;
 }
 
 // The path can point to either a dylib or a .tbd file.
diff --git a/lld/test/MachO/weak-sym.s b/lld/test/MachO/weak-sym.s
new file mode 100644
--- /dev/null
+++ b/lld/test/MachO/weak-sym.s
@@ -0,0 +1,43 @@
+# REQUIRES: x86
+# RUN: rm -rf %t; split-file %s %t
+
+# RUN: llvm-mc -filetype=obj -triple=x86_64-apple-iossimulator %t/lib_def.s -o %t/lib_def.o
+# RUN: llvm-mc -filetype=obj -triple=x86_64-apple-iossimulator %t/lib_weak.s -o %t/lib_weak.o
+# RUN: %lld -dylib -lSystem -dynamic  -platform_version ios-simulator 13.0.0 14.5 %t/lib_def.o %t/lib_weak.o -o %t/out.dylib
+
+#--- lib_def.s
+.section __TEXT,__text,regular,pure_instructions
+
+.globl  _uprv_getICUData_core
+
+_uprv_getICUData_core:
+  .cfi_startproc
+        pushq   %rbp
+        .cfi_def_cfa_offset 16
+        .cfi_offset %rbp, -16
+        movq    %rsp, %rbp
+        .cfi_def_cfa_register %rbp
+        popq    %rbp
+        retq
+        .cfi_endproc
+
+.subsections_via_symbols
+
+#--- lib_weak.s
+.section        __TEXT,__text,regular,pure_instructions
+
+.globl  _uprv_getICUData_core
+.weak_definition _uprv_getICUData_core
+
+_uprv_getICUData_core:
+  .cfi_startproc
+        pushq   %rbp
+        .cfi_def_cfa_offset 16
+        .cfi_offset %rbp, -16
+        movq    %rsp, %rbp
+        .cfi_def_cfa_register %rbp
+        popq    %rbp
+        retq
+        .cfi_endproc
+
+.subsections_via_symbols