diff --git a/llvm/lib/Transforms/Instrumentation/ThreadSanitizer.cpp b/llvm/lib/Transforms/Instrumentation/ThreadSanitizer.cpp
--- a/llvm/lib/Transforms/Instrumentation/ThreadSanitizer.cpp
+++ b/llvm/lib/Transforms/Instrumentation/ThreadSanitizer.cpp
@@ -72,6 +72,10 @@
     "tsan-distinguish-volatile", cl::init(false),
     cl::desc("Emit special instrumentation for accesses to volatiles"),
     cl::Hidden);
+static cl::opt<bool>  ClInstrumentReadBeforeWrite(
+    "tsan-instrument-read-before-write", cl::init(false),
+    cl::desc("Do not eliminate read instrumentation for read-before-writes"),
+    cl::Hidden);
 
 STATISTIC(NumInstrumentedReads, "Number of instrumented reads");
 STATISTIC(NumInstrumentedWrites, "Number of instrumented writes");
@@ -413,7 +417,7 @@
       Value *Addr = Load->getPointerOperand();
       if (!shouldInstrumentReadWriteFromAddress(I->getModule(), Addr))
         continue;
-      if (WriteTargets.count(Addr)) {
+      if (!ClInstrumentReadBeforeWrite && WriteTargets.count(Addr)) {
         // We will write to this temp, so no reason to analyze the read.
         NumOmittedReadsBeforeWrite++;
         continue;
diff --git a/llvm/test/Instrumentation/ThreadSanitizer/read_before_write.ll b/llvm/test/Instrumentation/ThreadSanitizer/read_before_write.ll
--- a/llvm/test/Instrumentation/ThreadSanitizer/read_before_write.ll
+++ b/llvm/test/Instrumentation/ThreadSanitizer/read_before_write.ll
@@ -1,4 +1,5 @@
 ; RUN: opt < %s -tsan -S | FileCheck %s
+; RUN: opt < %s -tsan -tsan-instrument-read-before-write -S | FileCheck %s --check-prefixes=CHECK,CHECK-UNOPT
 
 target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64-S128"
 
@@ -11,6 +12,7 @@
 }
 ; CHECK: define void @IncrementMe
 ; CHECK-NOT: __tsan_read
+; CHECK-UNOPT: __tsan_read
 ; CHECK: __tsan_write
 ; CHECK: ret void