[LoopUnrollRuntime] NFC: Refactored safety checks of unrolling multi-exit loop

Refactored the code and separated out a function
`canSafelyUnrollMultiExitLoop` to reduce redundant checks and make it
easier to add profitability heuristics later.
Added tests to runtime unrolling to make sure that unrolling for
multi-exit loops is not done unless the option
-unroll-runtime-multi-exit is true.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@307843 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 68 insertions, 0 deletions

diff --git a/test/Transforms/LoopUnroll/runtime-loop.ll b/test/Transforms/LoopUnroll/runtime-loop.ll
index 04661314eb1..878f4e8c78f 100644
--- a/test/Transforms/LoopUnroll/runtime-loop.ll
+++ b/test/Transforms/LoopUnroll/runtime-loop.ll
@@ -170,6 +170,74 @@ for.end:                                          ; preds = %for.cond.for.end_cr
   ret i16 %res.0.lcssa
 }
 
+; dont unroll loop with multiple exit/exiting blocks, unless
+; -runtime-unroll-multi-exit=true
+; single exit, multiple exiting blocks.
+define void @unique_exit(i32 %arg) {
+; PROLOG: unique_exit(
+; PROLOG-NOT: .unr
+
+; EPILOG: unique_exit(
+; EPILOG-NOT: .unr
+entry:
+  %tmp = icmp sgt i32 undef, %arg
+  br i1 %tmp, label %preheader, label %returnblock
+
+preheader:                                 ; preds = %entry
+  br label %header
+
+LoopExit:                                ; preds = %header, %latch
+  %tmp2.ph = phi i32 [ %tmp4, %header ], [ -1, %latch ]
+  br label %returnblock
+
+returnblock:                                         ; preds = %LoopExit, %entry
+  %tmp2 = phi i32 [ -1, %entry ], [ %tmp2.ph, %LoopExit ]
+  ret void
+
+header:                                           ; preds = %preheader, %latch
+  %tmp4 = phi i32 [ %inc, %latch ], [ %arg, %preheader ]
+  %inc = add nsw i32 %tmp4, 1
+  br i1 true, label %LoopExit, label %latch
+
+latch:                                            ; preds = %header
+  %cmp = icmp slt i32 %inc, undef
+  br i1 %cmp, label %header, label %LoopExit
+}
+
+; multiple exit blocks. don't unroll
+define void @multi_exit(i64 %trip, i1 %cond) {
+; PROLOG: multi_exit(
+; PROLOG-NOT: .unr
+
+; EPILOG: multi_exit(
+; EPILOG-NOT: .unr
+entry:
+  br label %loop_header
+
+loop_header:
+  %iv = phi i64 [ 0, %entry ], [ %iv_next, %loop_latch ]
+  br i1 %cond, label %loop_latch, label %loop_exiting_bb1
+
+loop_exiting_bb1:
+  br i1 false, label %loop_exiting_bb2, label %exit1
+
+loop_exiting_bb2:
+  br i1 false, label %loop_latch, label %exit3
+
+exit3:
+  ret void
+
+loop_latch:
+  %iv_next = add i64 %iv, 1
+  %cmp = icmp ne i64 %iv_next, %trip
+  br i1 %cmp, label %loop_header, label %exit2.loopexit
+
+exit1:
+ ret void
+
+exit2.loopexit:
+  ret void
+}
 !0 = distinct !{!0, !1}
 !1 = !{!"llvm.loop.unroll.runtime.disable"}