[PATCH] D18712: [LoopUnroll] Fix the way we update DT after complete unrolling.

[Michael Zolotukhin via llvm-commits]

mzolotukhin created this revision.
mzolotukhin added reviewers: dberlin, chandlerc, hfinkel, sanjoy, escha.
mzolotukhin added a subscriber: llvm-commits.

Updating dominators for exit-blocks of the unrolled loops is not enough,
as shown in PR27157. The proper way is to update dominators for all
dominance-children of exiting blocks. That set is a superset of
exit-blocks set.

http://reviews.llvm.org/D18712

Files:
  lib/Transforms/Utils/LoopUnroll.cpp
  test/Transforms/LoopUnroll/pr27157.ll

Index: test/Transforms/LoopUnroll/pr27157.ll
===================================================================
--- /dev/null
+++ test/Transforms/LoopUnroll/pr27157.ll
@@ -0,0 +1,30 @@
+; RUN: opt -loop-unroll -debug-only=loop-unroll -disable-output < %s
+; REQUIRES: asserts
+; Compile this test with debug flag on to verify domtree right after loop unrolling.
+target datalayout = "E-m:e-i1:8:16-i8:8:16-i64:64-f128:64-v128:64-a:8:16-n32:64"
+
+; PR27157
+define void @foo() {
+entry:
+  br label %loop_header
+loop_header:
+  %iv = phi i64 [ 0, %entry ], [ %iv_next, %loop_latch ]
+  br i1 undef, label %loop_latch, label %loop_exiting_bb1
+loop_exiting_bb1:
+  br i1 false, label %loop_exiting_bb2, label %exit1.loopexit
+loop_exiting_bb2:
+  br i1 false, label %loop_latch, label %bb
+bb:
+  br label %exit1
+loop_latch:
+  %iv_next = add nuw nsw i64 %iv, 1
+  %cmp = icmp ne i64 %iv_next, 2
+  br i1 %cmp, label %loop_header, label %exit2
+exit1.loopexit:
+  br label %exit1
+exit1:
+  ret void
+exit2:
+  ret void
+}
+
Index: lib/Transforms/Utils/LoopUnroll.cpp
===================================================================
--- lib/Transforms/Utils/LoopUnroll.cpp
+++ lib/Transforms/Utils/LoopUnroll.cpp
@@ -256,7 +256,9 @@
   // Are we eliminating the loop control altogether?
   bool CompletelyUnroll = Count == TripCount;
   SmallVector<BasicBlock *, 4> ExitBlocks;
+  SmallVector<BasicBlock *, 4> ExitingBlocks;
   L->getExitBlocks(ExitBlocks);
+  L->getExitingBlocks(ExitingBlocks);
 
   // Go through all exits of L and see if there are any phi-nodes there. We just
   // conservatively assume that they're inserted to preserve LCSSA form, which
@@ -554,11 +556,17 @@
   // the previous idom and the first latch, which dominates all copies of the
   // exiting block.
   if (DT && Count > 1) {
-    for (auto Exit : ExitBlocks) {
-      BasicBlock *PrevIDom = DT->getNode(Exit)->getIDom()->getBlock();
-      BasicBlock *NewIDom =
-          DT->findNearestCommonDominator(PrevIDom, Latches[0]);
-      DT->changeImmediateDominator(Exit, NewIDom);
+    for (auto BB : ExitingBlocks) {
+      auto *BBDomNode = DT->getNode(BB);
+      for (auto *ChildDomNode : BBDomNode->getChildren()) {
+        auto ChildBB = ChildDomNode->getBlock();
+        if (L->contains(ChildBB))
+          continue;
+        BasicBlock *PrevIDom = ChildDomNode->getIDom()->getBlock();
+        BasicBlock *NewIDom =
+            DT->findNearestCommonDominator(PrevIDom, Latches[0]);
+        DT->changeImmediateDominator(ChildBB, NewIDom);
+      }
     }
   }
 


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