[llvm] [LoopFusion] Validate loop structure before creating LoopCandidates (PR #192280)

[Ehsan Amiri via llvm-commits]

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@@ -363,7 +363,9 @@ struct FusionCandidate {
 
   bool reportInvalidCandidate(Statistic &Stat) const {
     using namespace ore;
-    assert(L && Preheader && "Fusion candidate not initialized properly!");
+    assert(L && "Fusion candidate has null loop!");
+    if (!Preheader)
+      return false;
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amehsan wrote:

alternatively you can modify this function so that it doesn't need the preheader. Header should always exist, so you can probably use the header for reporting. 

https://github.com/llvm/llvm-project/pull/192280