InstrProf: Make profile variables private to reduce binary size overhead

When we instrument a program for profiling, we copy the linkage of an
instrumented function so that our datastructures merge in the same way
as the function. This avoids redundant copies for things like
linkonce, but ends up emitting names we never need to reference for
normal and internal symbols. Promoting internal and external linkage
to private for these variables reduces the size overhead of profiling
drastically.

llvm-svn: 232799

1 files changed, 6 insertions, 2 deletions

diff --git a/clang/lib/CodeGen/CodeGenPGO.cpp b/clang/lib/CodeGen/CodeGenPGO.cpp
index a88335d0ac7..557828db0d0 100644
--- a/clang/lib/CodeGen/CodeGenPGO.cpp
+++ b/clang/lib/CodeGen/CodeGenPGO.cpp
@@ -58,12 +58,16 @@ void CodeGenPGO::setFuncName(llvm::Function *Fn) {
 }
 
 void CodeGenPGO::createFuncNameVar(llvm::GlobalValue::LinkageTypes Linkage) {
-  // Usually, we want to match the function's linkage, but
-  // available_externally and extern_weak both have the wrong semantics.
+  // We generally want to match the function's linkage, but available_externally
+  // and extern_weak both have the wrong semantics, and anything that doesn't
+  // need to link across compilation units doesn't need to be visible at all.
   if (Linkage == llvm::GlobalValue::ExternalWeakLinkage)
     Linkage = llvm::GlobalValue::LinkOnceAnyLinkage;
   else if (Linkage == llvm::GlobalValue::AvailableExternallyLinkage)
     Linkage = llvm::GlobalValue::LinkOnceODRLinkage;
+  else if (Linkage == llvm::GlobalValue::InternalLinkage ||
+           Linkage == llvm::GlobalValue::ExternalLinkage)
+    Linkage = llvm::GlobalValue::PrivateLinkage;
 
   auto *Value =
       llvm::ConstantDataArray::getString(CGM.getLLVMContext(), FuncName, false);