Make LoopDeletion check the maximum backedge taken count, rather than the

exact backedge taken count, when checking for infinite loops. This allows
it to delete loops with multiple exit conditions.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@84952 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 28 insertions, 1 deletions

diff --git a/lib/Transforms/Scalar/LoopDeletion.cpp b/lib/Transforms/Scalar/LoopDeletion.cpp
index 5f93756..8133a06 100644
--- a/lib/Transforms/Scalar/LoopDeletion.cpp
+++ b/lib/Transforms/Scalar/LoopDeletion.cpp
@@ -167,7 +167,7 @@ bool LoopDeletion::runOnLoop(Loop* L, LPPassManager& LPM) {
   // Don't remove loops for which we can't solve the trip count.
   // They could be infinite, in which case we'd be changing program behavior.
   ScalarEvolution& SE = getAnalysis<ScalarEvolution>();
-  const SCEV *S = SE.getBackedgeTakenCount(L);
+  const SCEV *S = SE.getMaxBackedgeTakenCount(L);
   if (isa<SCEVCouldNotCompute>(S))
     return Changed;
   
diff --git a/test/Transforms/LoopDeletion/multiple-exit-conditions.ll b/test/Transforms/LoopDeletion/multiple-exit-conditions.ll
new file mode 100644
index 0000000..87f8f46
--- /dev/null
+++ b/test/Transforms/LoopDeletion/multiple-exit-conditions.ll
@@ -0,0 +1,27 @@
+; RUN: opt < %s -loop-deletion -S | FileCheck %s
+
+; ScalarEvolution can prove the loop iteration is finite, even though
+; it can't represent the exact trip count as an expression. That's
+; good enough to let the loop be deleted.
+
+; CHECK:      entry:
+; CHECK-NEXT:   br label %return
+
+; CHECK:      return:
+; CHECK-NEXT:   ret void
+
+define void @foo(i64 %n, i64 %m) nounwind {
+entry:
+  br label %bb
+
+bb:
+  %x.0 = phi i64 [ 0, %entry ], [ %t0, %bb ]
+  %t0 = add i64 %x.0, 1
+  %t1 = icmp slt i64 %x.0, %n
+  %t3 = icmp sgt i64 %x.0, %m
+  %t4 = and i1 %t1, %t3
+  br i1 %t4, label %bb, label %return
+
+return:
+  ret void
+}