[llvm-bugs] [Bug 42552] New: Bad machine code: No live subrange at use

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=42552

            Bug ID: 42552
           Summary: Bad machine code: No live subrange at use
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Register Allocator
          Assignee: unassignedbugs at nondot.org
          Reporter: paulsson at linux.vnet.ibm.com
                CC: llvm-bugs at lists.llvm.org, quentin.colombet at gmail.com

Created attachment 22213
  --> https://bugs.llvm.org/attachment.cgi?id=22213&action=edit
reduced testcase

llc ./tc.ll -mtriple=s390x-linux-gnu -mcpu=z13 -o out.s -verify-machineinstrs
-systemz-subreg-liveness -lsr-complexity-limit=8 -consthoist-gep
-pre-RA-sched=list-ilp -disable-machine-licm -disable-machine-cse
-misched=ilpmin

*** Bad machine code: No live subrange at use ***
- function:    main
- basic block: %bb.5 bb132 (0x5db6d48) [1608B;4560B)
- instruction: 3600B    undef %182.subreg_h64:gr128bit = COPY
%181.subreg_h64:gr128bit
- operand 1:   %181.subreg_h64:gr128bit
- interval:    %181 [3476r,3600r:0)  0 at 3476r L00000008 [3476r,3600r:0)  0 at 3476r
weight:1.202965e+07
- at:          3600B
LLVM ERROR: Found 1 machine code errors.


There is something strange here: If I rename tc.ll to ./tc_nolive_subr_atuse.ll
there seem to be a random variation of the pre-RA-sched=list-ilp scheduler, as
the MF is not then identical, and the bug disappears! (I guess this should be
reported as a separate bug?)

What's more: if I do -stop/start-before=simple-register-coalescing, the bug
also becomes hidden...

I am using r365452 (2c0337f) "Retire VS2015 Support".

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