[CSSPGO][NFC] Fix a debug dump issue.

[hoy]

Summary

During context promotion, intermediate nodes that are on a call path but do not come with a profile can be promoted together with their parent nodes. Do not print sample context string for such nodes since they do not have profile.

[wenlei]

The printing and the wording were intentional - here we're promoting a context, and it doesn't have to be a context with profile. I wanted to capture the tree transformation, not limited to nodes with profile.

[hoy]

In D99441#2653814, @wenlei wrote:

The printing and the wording were intentional - here we're promoting a context, and it doesn't have to be a context with profile. I wanted to capture the tree transformation, not limited to nodes with profile.

I see. If there's a descendent node with a profile along the current path, the tree transformation can be captured by the promotion of the descendent later? The printing AVs because of a null ToNode->getFunctionSamples().

[wenlei]

In D99441#2653927, @hoy wrote:

In D99441#2653814, @wenlei wrote:

The printing and the wording were intentional - here we're promoting a context, and it doesn't have to be a context with profile. I wanted to capture the tree transformation, not limited to nodes with profile.

I see. If there's a descendent node with a profile along the current path, the tree transformation can be captured by the promotion of the descendent later? The printing AVs because of a null ToNode->getFunctionSamples().

Oh, I didn't notice the AV. In that case, avoid AV is more important. Thanks for the fix.

llvm/lib/Transforms/IPO/SampleContextTracker.cpp

ContextTrieNode &SampleContextTracker::promoteMergeContextSamplesTree(
   if (!ToNode) {
     // Do not delete node to move from its parent here because
     // caller is iterating over children of that parent node.
     ToNode = &ToNodeParent.moveToChildContext(
         NewCallSiteLoc, std::move(FromNode), ContextStrToRemove, false);
   } else {
     // Destination node exists, merge samples for the context tree
     mergeContextNode(FromNode, *ToNode, ContextStrToRemove);
-    LLVM_DEBUG(dbgs() << "  Context promoted and merged to: "
-                      << ToNode->getFunctionSamples()->getContext() << "\n");
+    LLVM_DEBUG({
+      if (ToNode->getFunctionSamples())
+        dbgs() << "  Context promoted and merged to: "
+               << ToNode->getFunctionSamples()->getContext() << "\n";
+    });
 
     // Recursively promote and merge children
     for (auto &It : FromNode.getAllChildContext()) {
       ContextTrieNode &FromChildNode = It.second;
       promoteMergeContextSamplesTree(FromChildNode, *ToNode,
                                      ContextStrToRemove);
     }