[llvm-bugs] [Bug 44541] New: Instcombine hangs with "opt -functionattrs -disable-basicaa -O1"

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=44541

            Bug ID: 44541
           Summary: Instcombine hangs with "opt -functionattrs
                    -disable-basicaa -O1"
           Product: new-bugs
           Version: unspecified
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: new bugs
          Assignee: unassignedbugs at nondot.org
          Reporter: mikael.holmen at ericsson.com
                CC: htmldeveloper at gmail.com, llvm-bugs at lists.llvm.org

Created attachment 23015
  --> https://bugs.llvm.org/attachment.cgi?id=23015&action=edit
bbi-37458_x86.ll reproducer

Running
 opt -functionattrs -disable-basicaa -O1 -S -o - ./bbi-37458_x86.ll
seems to hang forever.

Adding -debug-pass=Executions shows

 [2020-01-14 15:08:50.872376271] 0x611e690     Executing Pass 'Combine
redundant instructions' on Function 'test_sub3_4'...

and adding -debug gives repeated occurences of

IC: Visiting:   %_tmp2687 = select i1 %1808, i16 0, i16 %_tmp2685
IC: Visiting:   %1808 = icmp sgt i16 0, %_tmp2685
IC: Mod =   %1808 = icmp sgt i16 0, %_tmp2685
    New =   %1808 = icmp slt i16 %_tmp2682, 0
IC: ADD:   %_tmp2687 = select i1 %1808, i16 0, i16 %_tmp2685
IC: ADD:   %1808 = icmp slt i16 %_tmp2682, 0
IC: Visiting:   %1808 = icmp slt i16 %_tmp2682, 0
IC: Visiting:   %_tmp2687 = select i1 %1808, i16 0, i16 %_tmp2685


I've tried to reduce the command line to some minor variation of just
 opt -instcombine
but I can't seem to manage that. :/

The problem seems to be fairly old, I've seen it in builds from around late
March 2019.

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