[llvm-bugs] [Bug 38915] New: [InstCombine] Infinite loop by operating on same set of instructions in worklist

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=38915

            Bug ID: 38915
           Summary: [InstCombine] Infinite loop by operating on same set
                    of instructions in worklist
           Product: tools
           Version: trunk
          Hardware: PC
                OS: All
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: opt
          Assignee: unassignedbugs at nondot.org
          Reporter: anna at azul.com
                CC: llvm-bugs at lists.llvm.org

This test goes into infinite loop when run with InstCombine on llvm ToT:

opt -instcombine test.ll <-- hangs with rerunning IC over the same set of
instructions in the worklist.

test.ll:
define void @baz(i32 %arg) {
bb:
  switch i32 undef, label %bb4 [
    i32 0, label %bb2
    i32 1, label %bb3
    i32 2, label %bb1
  ]

bb1:                                              ; preds = %bb
  ret void

bb2:                                              ; preds = %bb
  unreachable

bb3:                                              ; preds = %bb
  ret void

bb4:                                              ; preds = %bb
  %tmp = sub i32 0, %arg
  %tmp5 = and i32 %tmp, 3
  %tmp6 = sub i32 0, %tmp5
  %tmp7 = sub i32 0, %tmp5
  %tmp8 = sub i32 -2, %tmp5
  %tmp9 = icmp sgt i32 %tmp6, -2147483647
  %tmp10 = select i1 %tmp9, i32 %tmp6, i32 -2147483647
  %tmp11 = mul i32 %tmp10, -1
  %tmp12 = icmp sgt i32 %tmp7, -2147483647
  %tmp13 = select i1 %tmp12, i32 %tmp7, i32 -2147483647
  %tmp14 = mul i32 %tmp13, -1
  %tmp15 = icmp sgt i32 %tmp11, %tmp14
  %tmp16 = select i1 %tmp15, i32 %tmp11, i32 %tmp14
  %tmp17 = sub i32 -1, %tmp16
  %tmp18 = icmp sgt i32 %tmp17, %tmp8
  %tmp19 = select i1 %tmp18, i32 %tmp17, i32 %tmp8
  %tmp20 = sub i32 -1, %tmp19
  %tmp21 = icmp sgt i32 %tmp20, 1
  %tmp22 = select i1 %tmp21, i32 %tmp20, i32 1
  %tmp23 = add i32 %tmp22, -1
  %tmp24 = add i32 %tmp5, -1
  %tmp25 = icmp sgt i32 %tmp24, %tmp23
  br i1 %tmp25, label %bb26, label %bb27

bb26:                                             ; preds = %bb4
  unreachable

bb27:                                             ; preds = %bb4
  unreachable
}

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