[PATCH] D41519: [BasicBlockUtils] Check for unreachable preds before updating LI in UpdateAnalysisInformation

[Anna Thomas via Phabricator via llvm-commits]

anna updated this revision to Diff 128016.
anna added a comment.

Simplified the testcase to make the issue clearer.


https://reviews.llvm.org/D41519

Files:
  lib/Transforms/Utils/BasicBlockUtils.cpp
  test/Transforms/LoopSimplify/unreachable-loop-pred.ll


Index: test/Transforms/LoopSimplify/unreachable-loop-pred.ll
===================================================================
--- test/Transforms/LoopSimplify/unreachable-loop-pred.ll
+++ test/Transforms/LoopSimplify/unreachable-loop-pred.ll
@@ -18,3 +18,52 @@
 foo:
   br label %while.body115
 }
+
+; When loopsimplify generates dedicated exit block for blocks that are landing
+; pads (i.e. innerLoopExit in this test), we should not get confused with the
+; unreachable pred (unreachableB) to innerLoopExit.
+define align 8 void @baz(i32 %trip) personality i32* ()* @wobble {
+entry:
+  br label %outerHeader
+
+outerHeader:
+  invoke void @foo() 
+          to label %innerPreheader unwind label %innerLoopExit
+
+innerPreheader:
+  br label %innerH
+
+innerH:
+  %tmp50 = invoke i8 * undef()
+          to label %innerLatch unwind label %innerLoopExit
+
+innerLatch:
+  %cmp = icmp slt i32 %trip, 42
+  br i1 %cmp, label %innerH, label %retblock
+
+unreachableB:                                             ; No predecessors!
+  %tmp62 = invoke i8 * undef()
+          to label %retblock unwind label %innerLoopExit
+
+; undedicated exit block (preds from inner and outer loop)
+; Also has unreachableB as pred.
+innerLoopExit:
+  %tmp65 = landingpad { i8*, i32 }
+          cleanup
+  invoke void @foo() 
+          to label %outerHeader unwind label %unwindblock
+
+unwindblock:
+  %tmp67 = landingpad { i8*, i32 }
+          cleanup
+  ret void
+
+retblock:
+  ret void
+}
+
+; Function Attrs: nounwind
+declare i32* @wobble()
+
+; Function Attrs: uwtable
+declare void @foo()
Index: lib/Transforms/Utils/BasicBlockUtils.cpp
===================================================================
--- lib/Transforms/Utils/BasicBlockUtils.cpp
+++ lib/Transforms/Utils/BasicBlockUtils.cpp
@@ -331,6 +331,12 @@
   bool IsLoopEntry = !!L;
   bool SplitMakesNewLoopHeader = false;
   for (BasicBlock *Pred : Preds) {
+    // Preds that are not reachable from entry should not be used to identify if
+    // OldBB is a loop entry or if SplitMakesNewLoopHeader. Unreachable blocks
+    // are not within any loops, so we incorrectly mark SplitMakesNewLoopHeader
+    // as true and make the NewBB the header of some loop. This breaks LI.
+    if (!DT->isReachableFromEntry(Pred))
+      continue;
     // If we need to preserve LCSSA, determine if any of the preds is a loop
     // exit.
     if (PreserveLCSSA)


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