1 files changed, 49 insertions, 0 deletions
diff --git a/llvm/test/Transforms/LoopUnroll/tripcount-overflow.ll b/llvm/test/Transforms/LoopUnroll/tripcount-overflow.ll
new file mode 100644
index 00000000000..0d5681b539a
--- /dev/null
+++ b/llvm/test/Transforms/LoopUnroll/tripcount-overflow.ll
@@ -0,0 +1,49 @@
+; RUN: opt < %s -S -unroll-runtime -unroll-count=2 -loop-unroll -unroll-runtime-epilog=true  | FileCheck %s -check-prefix=EPILOG
+; RUN: opt < %s -S -unroll-runtime -unroll-count=2 -loop-unroll -unroll-runtime-epilog=false | FileCheck %s -check-prefix=PROLOG
+target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
+
+; This test case documents how runtime loop unrolling handles the case
+; when the backedge-count is -1.
+
+; If %N, the backedge-taken count, is -1 then %0 unsigned-overflows
+; and is 0.  %xtraiter too is 0, signifying that the total trip-count
+; is divisible by 2.  The prologue then branches to the unrolled loop
+; and executes the 2^32 iterations there, in groups of 2.
+
+; EPILOG: entry:
+
+; EPILOG-NEXT: %0 = add i32 %N, 1
+; EPILOG-NEXT: %xtraiter = and i32 %0, 1
+; EPILOG-NEXT: %1 = icmp ult i32 %N, 1
+; EPILOG-NEXT: br i1 %1, label %while.end.unr-lcssa, label %entry.new
+; EPILOG: while.body:
+
+; EPILOG: %lcmp.mod = icmp ne i32 %xtraiter, 0
+; EPILOG-NEXT: br i1 %lcmp.mod, label %while.body.epil.preheader, label %while.end
+; EPILOG: while.body.epil:
+
+; PROLOG: entry:
+; PROLOG-NEXT: %0 = add i32 %N, 1
+; PROLOG-NEXT: %xtraiter = and i32 %0, 1
+; PROLOG-NEXT: %lcmp.mod = icmp ne i32 %xtraiter, 0
+; PROLOG-NEXT: br i1 %lcmp.mod, label %while.body.prol.preheader, label %while.body.prol.loopexit
+; PROLOG: while.body.prol:
+
+; PROLOG: %1 = icmp ult i32 %N, 1
+; PROLOG-NEXT: br i1 %1, label %while.end, label %entry.new
+; PROLOG: while.body:
+
+; Function Attrs: nounwind readnone ssp uwtable
+define i32 @foo(i32 %N) {
+entry:
+  br label %while.body
+
+while.body:                                       ; preds = %while.body, %entry
+  %i = phi i32 [ 0, %entry ], [ %inc, %while.body ]
+  %cmp = icmp eq i32 %i, %N
+  %inc = add i32 %i, 1
+  br i1 %cmp, label %while.end, label %while.body
+
+while.end:                                        ; preds = %while.body
+  ret i32 %i
+}