diff --git a/llvm/lib/ProfileData/SampleProfReader.cpp b/llvm/lib/ProfileData/SampleProfReader.cpp
--- a/llvm/lib/ProfileData/SampleProfReader.cpp
+++ b/llvm/lib/ProfileData/SampleProfReader.cpp
@@ -656,7 +656,7 @@
     if (hasSecFlag(Entry, SecProfSummaryFlags::SecFlagFullContext))
       FunctionSamples::ProfileIsCSFlat = ProfileIsCSFlat = true;
     if (hasSecFlag(Entry, SecProfSummaryFlags::SecFlagIsCSNested))
-      FunctionSamples::ProfileIsCSNested = ProfileIsCSNested;
+      FunctionSamples::ProfileIsCSNested = ProfileIsCSNested = true;
     if (hasSecFlag(Entry, SecProfSummaryFlags::SecFlagFSDiscriminator))
       FunctionSamples::ProfileIsFS = ProfileIsFS = true;
     break;
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
@@ -1542,6 +1542,10 @@
       continue;
     }
 
+    // Do not merge a context that is already duplicated into the base profile.
+    if (FS->getContext().hasAttribute(sampleprof::ContextDuplicatedIntoBase))
+      continue;
+
     if (ProfileMergeInlinee) {
       // A function call can be replicated by optimizations like callsite
       // splitting or jump threading and the replicates end up sharing the