[LoopUnrollRuntime] Avoid multi-exit nested loop with epilog generation

The loop structure for the outer loop does not contain the epilog
preheader when we try to unroll inner loop with multiple exits and
epilog code is generated. For now, we just bail out in such cases.
Added a test case that shows the problem. Without this bailout, we would
trip on assert saying LCSSA form is incorrect for outer loop.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@307676 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 44 insertions, 0 deletions

diff --git a/test/Transforms/LoopUnroll/runtime-loop-multiple-exits.ll b/test/Transforms/LoopUnroll/runtime-loop-multiple-exits.ll
index 18548c8af73..73672e14f78 100644
--- a/test/Transforms/LoopUnroll/runtime-loop-multiple-exits.ll
+++ b/test/Transforms/LoopUnroll/runtime-loop-multiple-exits.ll
@@ -434,3 +434,47 @@ loopexit1:                                             ; preds = %header
   %sext3 = phi i32 [ %shft, %header ]
   ret i32 %sext3
 }
+
+; Nested loop and inner loop is unrolled
+; FIXME: we cannot unroll with epilog remainder currently, because 
+; the outer loop does not contain the epilog preheader and epilog exit (while
+; infact it should). This causes us to choke up on LCSSA form being incorrect in
+; outer loop. However, the exit block where LCSSA fails, is infact still within
+; the outer loop. For now, we just bail out in presence of outer loop and epilog
+; loop is generated.
+; The outer loop header is the preheader for the inner loop and the inner header
+; branches back to the outer loop.
+define void @test8() {
+; EPILOG: test8(
+; EPILOG-NOT: niter
+
+; PROLOG: test8(
+; PROLOG: outerloop:
+; PROLOG-NEXT: phi i64 [ 3, %bb ], [ 0, %outerloop.loopexit ]
+; PROLOG:      %lcmp.mod = icmp eq i64
+; PROLOG-NEXT: br i1 %lcmp.mod, label %innerH.prol.loopexit, label %innerH.prol.preheader
+; PROLOG: latch.6:
+; PROLOG-NEXT: %tmp4.7 = add nsw i64 %tmp3, 8
+; PROLOG-NEXT: br i1 false, label %outerloop.loopexit.loopexit, label %latch.7
+; PROLOG: latch.7
+; PROLOG-NEXT: %tmp6.7 = icmp ult i64 %tmp4.7, 100
+; PROLOG-NEXT: br i1 %tmp6.7, label %innerH, label %exit.unr-lcssa
+bb:
+  br label %outerloop
+
+outerloop:                                              ; preds = %innerH, %bb
+  %tmp = phi i64 [ 3, %bb ], [ 0, %innerH ]
+  br label %innerH
+
+innerH:                                              ; preds = %latch, %outerloop
+  %tmp3 = phi i64 [ %tmp4, %latch ], [ %tmp, %outerloop ]
+  %tmp4 = add nuw nsw i64 %tmp3, 1
+  br i1 false, label %outerloop, label %latch
+
+latch:                                              ; preds = %innerH
+  %tmp6 = icmp ult i64 %tmp4, 100
+  br i1 %tmp6, label %innerH, label %exit
+
+exit:                                              ; preds = %latch
+  ret void
+}