[llvm] [Analysis] Fix null ptr dereference when using WriteGraph without branch probability info (PR #104102)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-analysis

Author: Tyler Nowicki (TylerNowicki)

<details>
<summary>Changes</summary>

The call to  'CFGInfo->getBPI()->getEdgeProbability(Node, SuccBB);' fails when BPI is not provided. In this case we can give up and not print any edge attributes.

---
Full diff: https://github.com/llvm/llvm-project/pull/104102.diff


1 Files Affected:

- (modified) llvm/include/llvm/Analysis/CFGPrinter.h (+4-3) 


``````````diff
diff --git a/llvm/include/llvm/Analysis/CFGPrinter.h b/llvm/include/llvm/Analysis/CFGPrinter.h
index 7d4d3a574b9e8..cd785331d1f14 100644
--- a/llvm/include/llvm/Analysis/CFGPrinter.h
+++ b/llvm/include/llvm/Analysis/CFGPrinter.h
@@ -265,18 +265,19 @@ struct DOTGraphTraits<DOTFuncInfo *> : public DefaultDOTGraphTraits {
   /// Display the raw branch weights from PGO.
   std::string getEdgeAttributes(const BasicBlock *Node, const_succ_iterator I,
                                 DOTFuncInfo *CFGInfo) {
+    // If BPI is not provided do not display any edge attributes
+    if (!CFGInfo->showEdgeWeights())
+      return "";
+
     unsigned OpNo = I.getSuccessorIndex();
     const Instruction *TI = Node->getTerminator();
     BasicBlock *SuccBB = TI->getSuccessor(OpNo);
     auto BranchProb = CFGInfo->getBPI()->getEdgeProbability(Node, SuccBB);
     double WeightPercent = ((double)BranchProb.getNumerator()) /
                            ((double)BranchProb.getDenominator());
-
     std::string TTAttr =
         formatv("tooltip=\"{0} -> {1}\\nProbability {2:P}\" ", getBBName(Node),
                 getBBName(SuccBB), WeightPercent);
-    if (!CFGInfo->showEdgeWeights())
-      return TTAttr;
 
     if (TI->getNumSuccessors() == 1)
       return TTAttr + "penwidth=2";

``````````

</details>


https://github.com/llvm/llvm-project/pull/104102