[llvm-bugs] [Bug 44462] New: X86FlagsCopyLowering.cpp fails to remove killed $eflags from successor live-ins

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=44462

            Bug ID: 44462
           Summary: X86FlagsCopyLowering.cpp fails to remove killed
                    $eflags from successor live-ins
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: Backend: X86
          Assignee: unassignedbugs at nondot.org
          Reporter: paulsson at linux.vnet.ibm.com
                CC: craig.topper at gmail.com, llvm-bugs at lists.llvm.org,
                    llvm-dev at redking.me.uk, spatel+llvm at rotateright.com

test/CodeGen/X86/copy-eflags.ll contains a function PR37100 which results in
this bug.

This was exposed by the (temporarily reverted) machine verifier improvement for
live-in lists (see https://reviews.llvm.org/D68267 which also has some
discussion about this test case).

https://reviews.llvm.org/D71375 is a suggested patch for
X86FlagsCopyLowering.cpp.

# After X86 EFLAGS copy lowering

bb.1.bb1:
...
  TEST8rr %23:gr8, %23:gr8, implicit-def $eflags
  JCC_1 %bb.3, 5, implicit killed $eflags

bb.2.bb1:
; predecessors: %bb.1
  successors: %bb.3(0x80000000); %bb.3(100.00%)
  liveins: $eflags

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