diff --git a/llvm/lib/Transforms/IPO/SampleProfile.cpp b/llvm/lib/Transforms/IPO/SampleProfile.cpp
--- a/llvm/lib/Transforms/IPO/SampleProfile.cpp
+++ b/llvm/lib/Transforms/IPO/SampleProfile.cpp
@@ -143,6 +143,12 @@
              "callsite and function as having 0 samples. Otherwise, treat "
              "un-sampled callsites and functions conservatively as unknown. "));
 
+static cl::opt<bool> ProfileSampleBlockAccurate(
+    "profile-sample-block-accurate", cl::Hidden, cl::init(false),
+    cl::desc("If the sample profile is accurate, we will mark all un-sampled "
+             "branches and calls as having 0 samples. Otherwise, treat "
+             "them conservatively as unknown. "));
+
 static cl::opt<bool> ProfileAccurateForSymsInList(
     "profile-accurate-for-symsinlist", cl::Hidden, cl::ZeroOrMore,
     cl::init(true),
@@ -1529,7 +1535,7 @@
                             {static_cast<uint32_t>(BlockWeights[BB])}));
         }
       }
-    } else if (OverwriteExistingWeights) {
+    } else if (OverwriteExistingWeights || ProfileSampleBlockAccurate) {
       // Set profile metadata (possibly annotated by LTO prelink) to zero or
       // clear it for cold code.
       for (auto &I : BB->getInstList()) {