[PGO] Do not emit runtime hook user function for Linux

Clang driver now injects -u<hook_var> flag in the linker 
command line, in which case user function is not needed 
any more.

Differential Revision: http://reviews.llvm.org/D14033

llvm-svn: 251612

1 files changed, 5 insertions, 0 deletions

diff --git a/llvm/lib/Transforms/Instrumentation/InstrProfiling.cpp b/llvm/lib/Transforms/Instrumentation/InstrProfiling.cpp
index 55fd86f7172..493c70e8fd6 100644
--- a/llvm/lib/Transforms/Instrumentation/InstrProfiling.cpp
+++ b/llvm/lib/Transforms/Instrumentation/InstrProfiling.cpp
@@ -288,6 +288,11 @@ void InstrProfiling::emitRegistration() {
 
 void InstrProfiling::emitRuntimeHook() {
 
+  // We expect the linker to be invoked with -u<hook_var> flag for linux,
+  // for which case there is no need to emit the user function.
+  if (Triple(M->getTargetTriple()).isOSLinux())
+    return;
+
   // If the module's provided its own runtime, we don't need to do anything.
   if (M->getGlobalVariable(getInstrProfRuntimeHookVarName())) return;