[PATCH] D72519: [LoopInfo] Support multi edge in getLoopLatch()

[Nikita Popov via Phabricator via llvm-commits]

nikic created this revision.
nikic added reviewers: efriedma, reames, sanjoy.google.
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Change split out from D72420 <https://reviews.llvm.org/D72420>, because I noticed it causes an unrelated test change. If the loop latch is a switch, then there can be multiple edges from the latch to the header. The LoopSimplify test changes because it's no longer necessary to split of an extra block in this case.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D72519

Files:
  llvm/include/llvm/Analysis/LoopInfoImpl.h
  llvm/test/Transforms/LoopSimplify/basictest.ll


Index: llvm/test/Transforms/LoopSimplify/basictest.ll
===================================================================
--- llvm/test/Transforms/LoopSimplify/basictest.ll
+++ llvm/test/Transforms/LoopSimplify/basictest.ll
@@ -44,17 +44,15 @@
 ; CHECK-NEXT:    br label [[LOOP:%.*]]
 ; CHECK:       loop:
 ; CHECK-NEXT:    [[B:%.*]] = load volatile i8, i8* [[B_PTR:%.*]]
-; CHECK-NEXT:    switch i8 [[B]], label [[LOOP_BACKEDGE:%.*]] [
+; CHECK-NEXT:    switch i8 [[B]], label [[LOOP]] [
 ; CHECK-NEXT:    i8 0, label [[EXIT_A_LOOPEXIT:%.*]]
 ; CHECK-NEXT:    i8 1, label [[EXIT_B_LOOPEXIT:%.*]]
-; CHECK-NEXT:    i8 2, label [[LOOP_BACKEDGE]]
+; CHECK-NEXT:    i8 2, label [[LOOP]]
 ; CHECK-NEXT:    i8 3, label [[EXIT_A_LOOPEXIT]]
-; CHECK-NEXT:    i8 4, label [[LOOP_BACKEDGE]]
+; CHECK-NEXT:    i8 4, label [[LOOP]]
 ; CHECK-NEXT:    i8 5, label [[EXIT_A_LOOPEXIT]]
-; CHECK-NEXT:    i8 6, label [[LOOP_BACKEDGE]]
+; CHECK-NEXT:    i8 6, label [[LOOP]]
 ; CHECK-NEXT:    ]
-; CHECK:       loop.backedge:
-; CHECK-NEXT:    br label [[LOOP]]
 ; CHECK:       exit.a.loopexit:
 ; CHECK-NEXT:    br label [[EXIT_A]]
 ; CHECK:       exit.a:
Index: llvm/include/llvm/Analysis/LoopInfoImpl.h
===================================================================
--- llvm/include/llvm/Analysis/LoopInfoImpl.h
+++ llvm/include/llvm/Analysis/LoopInfoImpl.h
@@ -211,7 +211,7 @@
   BlockT *Header = getHeader();
   BlockT *Latch = nullptr;
   for (const auto Pred : children<Inverse<BlockT *>>(Header)) {
-    if (contains(Pred)) {
+    if (Latch != Pred && contains(Pred)) {
       if (Latch)
         return nullptr;
       Latch = Pred;


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