Fix loop unswitching's assumption that a code path which either

infinite loops or exits will eventually exit. This fixes PR5373.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@112745 91177308-0d34-0410-b5e6-96231b3b80d8

test/Transforms/LoopUnswitch/infinite-loop.ll

@@ -0,0 +1,53 @@
+; RUN: opt -loop-unswitch -disable-output -stats -info-output-file - < %s | FileCheck --check-prefix=STATS %s
+; RUN: opt -loop-unswitch -simplifycfg -S < %s | FileCheck %s
+; PR5373
+
+; Loop unswitching shouldn't trivially unswitch the true case of condition %a
+; in the code here because it leads to an infinite loop. While this doesn't
+; contain any instructions with side effects, it's still a kind of side effect.
+; It can trivially unswitch on the false cas of condition %a though.
+
+; STATS: 2 loop-unswitch - Number of branches unswitched
+; STATS: 1 loop-unswitch - Number of unswitches that are trivial
+
+; CHECK: @func_16
+; CHECK-NEXT: entry:
+; CHECK-NEXT: br i1 %a, label %entry.split, label %abort0.split
+
+; CHECK: entry.split:
+; CHECK-NEXT: br i1 %b, label %cond.end.us, label %abort1
+
+; CHECK: cond.end.us:
+; CHECK-NEXT: br label %cond.end.us
+
+; CHECK: abort0.split:
+; CHECK-NEXT: call void @end0() noreturn nounwind
+; CHECK-NEXT: unreachable
+
+; CHECK: abort1:
+; CHECK-NEXT: call void @end1() noreturn nounwind
+; CHECK-NEXT: unreachable
+
+; CHECK: }
+
+define void @func_16(i1 %a, i1 %b) nounwind {
+entry:
+  br label %for.body
+
+for.body:
+  br i1 %a, label %cond.end, label %abort0
+
+cond.end:
+  br i1 %b, label %for.body, label %abort1
+
+abort0:
+  call void @end0() noreturn nounwind
+  unreachable
+
+abort1:
+  call void @end1() noreturn nounwind
+  unreachable
+}
+
+declare void @end0() noreturn
+declare void @end1() noreturn