[llvm] r339983 - [NFC] Add tests to ensure that improvement of MustThrow analysis will not lead to problems in future

[Max Kazantsev via llvm-commits]

Author: mkazantsev
Date: Thu Aug 16 22:20:25 2018
New Revision: 339983

URL: http://llvm.org/viewvc/llvm-project?rev=339983&view=rev
Log:
[NFC] Add tests to ensure that improvement of MustThrow analysis will not lead to problems in future

Modified:
    llvm/trunk/test/Transforms/LICM/infinite_loops.ll

Modified: llvm/trunk/test/Transforms/LICM/infinite_loops.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/LICM/infinite_loops.ll?rev=339983&r1=339982&r2=339983&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/LICM/infinite_loops.ll (original)
+++ llvm/trunk/test/Transforms/LICM/infinite_loops.ll Thu Aug 16 22:20:25 2018
@@ -40,3 +40,94 @@ backedge:
 exit:
   ret void
 }
+
+; The test above is UB in C++, because there is a requirement that any
+; thead should eventually terminate, execute volatile access operation, call IO
+; or synchronize. In spite of that, the behavior in the test above *might* be
+; correct. This one is equivalent to the test above, but it has a volatile
+; memory access in the loop's mustexec block, so the compiler no longer has a
+; right to assume that it must terminate. Show that the same problem persists,
+; and that it was a bug and not a cool optimization based on loop infinity.
+; By the moment when this test was added, it was accidentally correct due to
+; reasons not directly related to this piece of logic. Make sure that it keeps
+; correct in the future.
+define void @test_impossible_exit_in_untaken_block_no_ub(i32 %a, i32 %b, i32* noalias %p, i32* noalias %vp) {
+; CHECK-LABEL: @test_impossible_exit_in_untaken_block_no_ub(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    br label [[LOOP:%.*]]
+; CHECK:       loop:
+; CHECK-NEXT:    [[IV:%.*]] = phi i32 [ 0, [[ENTRY:%.*]] ], [ [[IV_NEXT:%.*]], [[BACKEDGE:%.*]] ]
+; CHECK-NEXT:    [[TMP0:%.*]] = load volatile i32, i32* [[VP:%.*]]
+; CHECK-NEXT:    br i1 false, label [[NEVER_TAKEN:%.*]], label [[BACKEDGE]]
+; CHECK:       never_taken:
+; CHECK-NEXT:    [[DIV:%.*]] = sdiv i32 [[A:%.*]], [[B:%.*]]
+; CHECK-NEXT:    store i32 [[DIV]], i32* [[P:%.*]]
+; CHECK-NEXT:    br i1 true, label [[BACKEDGE]], label [[EXIT:%.*]]
+; CHECK:       backedge:
+; CHECK-NEXT:    [[IV_NEXT]] = add i32 [[IV]], 1
+; CHECK-NEXT:    br label [[LOOP]]
+; CHECK:       exit:
+; CHECK-NEXT:    ret void
+;
+entry:
+  br label %loop
+
+loop:
+  %iv = phi i32 [ 0, %entry ], [ %iv.next, %backedge ]
+  load volatile i32, i32* %vp
+  br i1 false, label %never_taken, label %backedge
+
+never_taken:
+  %div = sdiv i32 %a, %b
+  store i32 %div, i32* %p
+  br i1 true, label %backedge, label %exit
+
+backedge:
+  %iv.next = add i32 %iv, 1
+  br label %loop
+
+exit:
+  ret void
+}
+
+; Same as above, but the volatile access is in mustexecute backedge block. The
+; loop is no longer "finite by specification", make sure we don't hoist sdiv
+; from it no matter how general the MustThrow analysis is.
+define void @test_impossible_exit_in_untaken_block_no_ub_2(i32 %a, i32 %b, i32* noalias %p, i32* noalias %vp) {
+; CHECK-LABEL: @test_impossible_exit_in_untaken_block_no_ub_2(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    br label [[LOOP:%.*]]
+; CHECK:       loop:
+; CHECK-NEXT:    [[IV:%.*]] = phi i32 [ 0, [[ENTRY:%.*]] ], [ [[IV_NEXT:%.*]], [[BACKEDGE:%.*]] ]
+; CHECK-NEXT:    br i1 false, label [[NEVER_TAKEN:%.*]], label [[BACKEDGE]]
+; CHECK:       never_taken:
+; CHECK-NEXT:    [[DIV:%.*]] = sdiv i32 [[A:%.*]], [[B:%.*]]
+; CHECK-NEXT:    store i32 [[DIV]], i32* [[P:%.*]]
+; CHECK-NEXT:    br i1 true, label [[BACKEDGE]], label [[EXIT:%.*]]
+; CHECK:       backedge:
+; CHECK-NEXT:    [[IV_NEXT]] = add i32 [[IV]], 1
+; CHECK-NEXT:    [[TMP0:%.*]] = load volatile i32, i32* [[VP:%.*]]
+; CHECK-NEXT:    br label [[LOOP]]
+; CHECK:       exit:
+; CHECK-NEXT:    ret void
+;
+entry:
+  br label %loop
+
+loop:
+  %iv = phi i32 [ 0, %entry ], [ %iv.next, %backedge ]
+  br i1 false, label %never_taken, label %backedge
+
+never_taken:
+  %div = sdiv i32 %a, %b
+  store i32 %div, i32* %p
+  br i1 true, label %backedge, label %exit
+
+backedge:
+  %iv.next = add i32 %iv, 1
+  load volatile i32, i32* %vp
+  br label %loop
+
+exit:
+  ret void
+}