[llvm] [CodeGen] Ignore requiresStructuredCFG check in canSplitCriticalEdge if successor is loop header (PR #154063)

[Wenju He via llvm-commits]

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@@ -1403,7 +1403,15 @@ bool MachineBasicBlock::canSplitCriticalEdge(
   const MachineFunction *MF = getParent();
   // Performance might be harmed on HW that implements branching using exec mask
   // where both sides of the branches are always executed.
-  if (MF->getTarget().requiresStructuredCFG())
+  // However, if `Succ` is a loop header, splitting the critical edge will not
+  // break structured CFG.
+  auto SuccIsLoopHeader = [&]() {
+    if (MLI)
+      if (MachineLoop *L = MLI->getLoopFor(Succ); L && L->getHeader() == Succ)
+        return true;
+    return false;
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wenju-he wrote:

> This also doesn't need to be a lambda

done, thanks

https://github.com/llvm/llvm-project/pull/154063