LoopUnroll: Create sub-loops in LoopInfo

`LoopUnrollPass` says that it preserves `LoopInfo` -- make it so.  In
particular, tell `LoopInfo` about copies of inner loops when unrolling
the outer loop.

Conservatively, also tell `ScalarEvolution` to forget about the original
versions of these loops, since their inputs may have changed.

Fixes PR20987.

llvm-svn: 219241

1 files changed, 35 insertions, 0 deletions

diff --git a/llvm/test/Transforms/LoopUnroll/update-loop-info-in-subloops.ll b/llvm/test/Transforms/LoopUnroll/update-loop-info-in-subloops.ll
new file mode 100644
index 00000000000..adbf47defe8
--- /dev/null
+++ b/llvm/test/Transforms/LoopUnroll/update-loop-info-in-subloops.ll
@@ -0,0 +1,35 @@
+; RUN: opt -S < %s -loop-unroll -block-freq | FileCheck %s
+; Crasher from PR20987.
+
+; CHECK: define void @update_loop_info_in_subloops
+; CHECK: entry:
+; CHECK: L:
+; CHECK: L.inner:
+; CHECK: L.inner.latch:
+; CHECK: L.latch:
+; CHECK: L.inner.1:
+; CHECK: L.inner.latch.1:
+; CHECK: L.latch.1:
+
+define void @update_loop_info_in_subloops() {
+entry:
+  br label %L
+
+L:
+  %0 = phi i64 [ 1, %entry ], [ %1, %L.latch ]
+  br label %L.inner
+
+L.inner:
+  br label %L.inner.latch
+
+L.inner.latch:
+  br i1 false, label %L.latch, label %L.inner
+
+L.latch:
+  %1 = add i64 %0, 1
+  %2 = icmp eq i64 %1, 3
+  br i1 %2, label %exit, label %L
+
+exit:
+  ret void
+}