[msan] Put msan constructor in a comdat.

MSan adds a constructor to each translation unit that calls
__msan_init, and does nothing else. The idea is to run __msan_init
before any instrumented code. This results in multiple constructors
and multiple .init_array entries in the final binary, one per
translation unit. This is absolutely unnecessary; one would be
enough.

This change moves the constructors to a comdat group in order to drop
the extra ones.

llvm-svn: 260632

1 files changed, 3 insertions, 1 deletions

diff --git a/llvm/lib/Transforms/Instrumentation/MemorySanitizer.cpp b/llvm/lib/Transforms/Instrumentation/MemorySanitizer.cpp
index b26a4b55505..6ebf6e20a4a 100644
--- a/llvm/lib/Transforms/Instrumentation/MemorySanitizer.cpp
+++ b/llvm/lib/Transforms/Instrumentation/MemorySanitizer.cpp
@@ -540,8 +540,10 @@ bool MemorySanitizer::doInitialization(Module &M) {
       createSanitizerCtorAndInitFunctions(M, kMsanModuleCtorName, kMsanInitName,
                                           /*InitArgTypes=*/{},
                                           /*InitArgs=*/{});
+  Comdat *MsanCtorComdat = M.getOrInsertComdat(kMsanModuleCtorName);
+  MsanCtorFunction->setComdat(MsanCtorComdat);
 
-  appendToGlobalCtors(M, MsanCtorFunction, 0);
+  appendToGlobalCtors(M, MsanCtorFunction, 0, MsanCtorFunction);
 
   if (TrackOrigins)
     new GlobalVariable(M, IRB.getInt32Ty(), true, GlobalValue::WeakODRLinkage,