[PATCH] D125574: [BasicBlockUtils] Do not move loop metadata if outer loop header.

[Hendrik Greving via Phabricator via llvm-commits]

hgreving updated this revision to Diff 429348.
hgreving added a comment.

Whoa another corner case.


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D125574/new/

https://reviews.llvm.org/D125574

Files:
  llvm/lib/Transforms/Utils/BasicBlockUtils.cpp
  llvm/test/Transforms/LoopSimplify/update_latch_md2.ll


Index: llvm/test/Transforms/LoopSimplify/update_latch_md2.ll
===================================================================
--- /dev/null
+++ llvm/test/Transforms/LoopSimplify/update_latch_md2.ll
@@ -0,0 +1,34 @@
+; Tests loop-simplify does not move the loop metadata, because
+; the loopexit block is not the latch of the loop _bb6.
+
+; RUN: opt < %s -loop-simplify -S | FileCheck %s
+; CHECK-LABEL: _bb7.loopexit:
+; CHECK-NOT: br label %_bb7, !llvm.loop !0
+; CHECK-LABEL: _bb6:
+; CHECK: br i1 %p, label %_bb6, label %_bb7.loopexit, !llvm.loop !0
+
+define void @func(i1 %p) {
+_bb1:
+  br label %_bb7
+
+_bb7:
+  br i1 %p, label %_bb4, label %_bb2
+
+_bb4:
+  br i1 %p, label %_bb5, label %_bb3
+
+_bb5:
+  br label %_bb3
+
+_bb3:
+  br label %_bb6
+
+_bb6:
+  br i1 %p, label %_bb6, label %_bb7, !llvm.loop !0
+
+_bb2:
+  ret void
+}
+
+!0 = distinct !{!0, !1}
+!1 = !{!"llvm.loop.mustprogress"}
Index: llvm/lib/Transforms/Utils/BasicBlockUtils.cpp
===================================================================
--- llvm/lib/Transforms/Utils/BasicBlockUtils.cpp
+++ llvm/lib/Transforms/Utils/BasicBlockUtils.cpp
@@ -1158,11 +1158,16 @@
   }
 
   if (OldLatch) {
-    BasicBlock *NewLatch = L->getLoopLatch();
-    if (NewLatch != OldLatch) {
-      MDNode *MD = OldLatch->getTerminator()->getMetadata("llvm.loop");
-      NewLatch->getTerminator()->setMetadata("llvm.loop", MD);
-      OldLatch->getTerminator()->setMetadata("llvm.loop", nullptr);
+    Loop *IL = LI->getLoopFor(OldLatch);
+    // It's still possible that OldLatch is the latch of another inner loop, in
+    // which case we do not move the metadata.
+    if (IL && IL->getLoopLatch() != OldLatch) {
+      BasicBlock *NewLatch = L->getLoopLatch();
+      if (NewLatch != OldLatch) {
+        MDNode *MD = OldLatch->getTerminator()->getMetadata("llvm.loop");
+        NewLatch->getTerminator()->setMetadata("llvm.loop", MD);
+        OldLatch->getTerminator()->setMetadata("llvm.loop", nullptr);
+      }
     }
   }
 


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