Merging r276015:

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r276015 | vedantk | 2016-07-19 13:16:08 -0700 (Tue, 19 Jul 2016) | 7 lines

[tsan] Don't instrument __llvm_gcov_global_state_pred or __llvm_gcda*

r274801 did not go far enough to allow gcov+tsan to cooperate. With this
commit it's possible to run the following code without false positives:

  std::thread T1(fib), T2(fib);
  T1.join(); T2.join();
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git-svn-id: https://llvm.org/svn/llvm-project/llvm/branches/release_39@276810 91177308-0d34-0410-b5e6-96231b3b80d8

Author: zmodem

lib/Transforms/Instrumentation/ThreadSanitizer.cpp

@@ -272,8 +272,9 @@ static bool shouldInstrumentReadWriteFromAddress(Value *Addr) {
         return false;
     }
 
-    // Check if the global is in a GCOV counter array.
-    if (GV->getName().startswith("__llvm_gcov_ctr"))
+    // Check if the global is private gcov data.
+    if (GV->getName().startswith("__llvm_gcov") ||
+        GV->getName().startswith("__llvm_gcda"))
       return false;
   }
 

test/Instrumentation/ThreadSanitizer/do-not-instrument-memory-access.ll

@@ -13,6 +13,8 @@ target triple = "x86_64-apple-macosx10.9"
 
 @__llvm_gcov_ctr = internal global [1 x i64] zeroinitializer
 @__llvm_gcov_ctr.1 = internal global [1 x i64] zeroinitializer
+@__llvm_gcov_global_state_pred = internal global i32 0
+@__llvm_gcda_foo = internal global i32 0
 
 define i32 @test_gep() sanitize_thread {
 entry:
@@ -42,5 +44,16 @@ entry:
   ret i32 undef
 }
 
+define void @test_load() sanitize_thread {
+entry:
+  %0 = load i32, i32* @__llvm_gcov_global_state_pred
+  store i32 1, i32* @__llvm_gcov_global_state_pred
+
+  %1 = load i32, i32* @__llvm_gcda_foo
+  store i32 1, i32* @__llvm_gcda_foo
+
+  ret void
+}
+
 ; CHECK-NOT: {{call void @__tsan_write}}
 ; CHECK: __tsan_init