[llvm] [DFAJumpThreading] Prevent pass from using too much memory. (PR #145482)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-transforms

Author: Bushev Dmitry (dybv-sc)

<details>
<summary>Changes</summary>

The limit 'dfa-max-num-paths' that is used to control number of enumerated paths was not checked against inside getPathsFromStateDefMap. It may lead to large memory consumption for complex enough switch statements.

---
Full diff: https://github.com/llvm/llvm-project/pull/145482.diff


1 Files Affected:

- (modified) llvm/lib/Transforms/Scalar/DFAJumpThreading.cpp (+8) 


``````````diff
diff --git a/llvm/lib/Transforms/Scalar/DFAJumpThreading.cpp b/llvm/lib/Transforms/Scalar/DFAJumpThreading.cpp
index 938aab5879044..ac7af712bcf12 100644
--- a/llvm/lib/Transforms/Scalar/DFAJumpThreading.cpp
+++ b/llvm/lib/Transforms/Scalar/DFAJumpThreading.cpp
@@ -618,6 +618,8 @@ struct AllSwitchPaths {
 
     VisitedBlocks UniqueBlocks;
     for (auto *IncomingBB : Phi->blocks()) {
+      if(Res.size() >= MaxNumPaths)
+        break;
       if (!UniqueBlocks.insert(IncomingBB).second)
         continue;
       if (!SwitchOuterLoop->contains(IncomingBB))
@@ -657,6 +659,8 @@ struct AllSwitchPaths {
             getPathsFromStateDefMap(StateDef, IncomingPhi, VB);
         for (ThreadingPath &Path : PredPaths) {
           Path.push_back(PhiBB);
+          if(Res.size() >= MaxNumPaths)
+            break;
           Res.push_back(std::move(Path));
         }
         continue;
@@ -679,6 +683,10 @@ struct AllSwitchPaths {
           ThreadingPath NewPath(Path);
           NewPath.appendExcludingFirst(IPath);
           NewPath.push_back(PhiBB);
+          if(Res.size() >= MaxNumPaths) {
+            VB.erase(PhiBB);
+            return Res;
+	  }
           Res.push_back(NewPath);
         }
       }

``````````

</details>


https://github.com/llvm/llvm-project/pull/145482