[llvm] [AMDGPU] Teach SIPreEmitPeephole pass to preserve MachineLoopInfo (PR #178868)

[Dark Steve via llvm-commits]

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@@ -101,6 +113,50 @@ char SIPreEmitPeepholeLegacy::ID = 0;
 
 char &llvm::SIPreEmitPeepholeID = SIPreEmitPeepholeLegacy::ID;
 
+void SIPreEmitPeephole::updateMLIBeforeRemovingEdge(
+    MachineBasicBlock *From, MachineBasicBlock *To) const {
+  if (!MLI)
+    return;
+
+  // Only handle back-edges: To must be a loop header with From inside the loop.
+  MachineLoop *Loop = MLI->getLoopFor(To);
+  if (!Loop || Loop->getHeader() != To || !Loop->contains(From))
+    return;
+
+  // Count back-edges
+  unsigned BackEdgeCount = 0;
+  for (MachineBasicBlock *Pred : To->predecessors()) {
+    if (Loop->contains(Pred))
+      BackEdgeCount++;
+  }
+
+  if (BackEdgeCount <= 1) {
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PrasoonMishra wrote:

Done.

https://github.com/llvm/llvm-project/pull/178868