[MachineLoopInfo] Fix getLoopID to handle multi latches. (#106195)

This patch also fixed `CodegenPrepare` to preserve loop metadata when
merging blocks.

This fixes issue #102632

1 files changed, 6 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/CodeGenPrepare.cpp b/llvm/lib/CodeGen/CodeGenPrepare.cpp
index bf48c1f..da6c758 100644
--- a/llvm/lib/CodeGen/CodeGenPrepare.cpp
+++ b/llvm/lib/CodeGen/CodeGenPrepare.cpp
@@ -1183,6 +1183,12 @@ void CodeGenPrepare::eliminateMostlyEmptyBlock(BasicBlock *BB) {
     }
   }
 
+  // Preserve loop Metadata.
+  if (BI->hasMetadata(LLVMContext::MD_loop)) {
+    for (auto *Pred : predecessors(BB))
+      Pred->getTerminator()->copyMetadata(*BI, LLVMContext::MD_loop);
+  }
+
   // The PHIs are now updated, change everything that refers to BB to use
   // DestBB and remove BB.
   BB->replaceAllUsesWith(DestBB);