PGO: Don't define instrumentation data available_externally

Variables with available_externally linkage can be dropped at will.
This causes link errors, since there are still references to the
instrumentation!  linkonce_odr is almost equivalent, so use that
instead.

As a drive-by fix (I don't have an Elf system, so I'm not sure how to
write a testcase), use linkonce linkage for the instrumentation of
extern_weak functions.

<rdar://problem/15943240>

llvm-svn: 204408

1 files changed, 15 insertions, 0 deletions

diff --git a/clang/lib/CodeGen/CodeGenPGO.cpp b/clang/lib/CodeGen/CodeGenPGO.cpp
index 0dfecfc36cd..99109f42e41 100644
--- a/clang/lib/CodeGen/CodeGenPGO.cpp
+++ b/clang/lib/CodeGen/CodeGenPGO.cpp
@@ -824,7 +824,22 @@ void CodeGenPGO::assignRegionCounters(const Decl *D, llvm::Function *Fn) {
   if (!D)
     return;
   setFuncName(Fn);
+
+  // Set the linkage for variables based on the function linkage.  Usually, we
+  // want to match it, but available_externally and extern_weak both have the
+  // wrong semantics.
   VarLinkage = Fn->getLinkage();
+  switch (VarLinkage) {
+  case llvm::GlobalValue::ExternalWeakLinkage:
+    VarLinkage = llvm::GlobalValue::LinkOnceAnyLinkage;
+    break;
+  case llvm::GlobalValue::AvailableExternallyLinkage:
+    VarLinkage = llvm::GlobalValue::LinkOnceODRLinkage;
+    break;
+  default:
+    break;
+  }
+
   mapRegionCounters(D);
   if (InstrumentRegions)
     emitCounterVariables();