[llvm-bugs] [Bug 27156] New: VirtRegMap.cpp should not just remove an identity copy which also has a impl-def of a super-reg

[via llvm-bugs]

https://llvm.org/bugs/show_bug.cgi?id=27156

            Bug ID: 27156
           Summary: VirtRegMap.cpp should not just remove an identity copy
                    which also has a impl-def of a super-reg
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: Register Allocator
          Assignee: unassignedbugs at nondot.org
          Reporter: paulsson at linux.vnet.ibm.com
                CC: llvm-bugs at lists.llvm.org, matze at braunis.de
    Classification: Unclassified

Created attachment 16137
  --> https://llvm.org/bugs/attachment.cgi?id=16137&action=edit
clang input

VirtRegMap removes identity copies, but that leads to machine-verifier
complaints if there is a def of a super reg as well.

I am not sure what the best fix is, but the patch attached seems to fix this by
transforming the COPY to an IMPLICIT_DEF when there is a def of a super-reg.
The patch assumes (arbitrarily) that there could only be one extra operand -
not sure if this is always true...

./bin/clang -cc1 -triple s390x-ibm-linux -S -disable-free -main-file-name
expr.c -mrelocation-model static -mthread-model posix -fmath-errno
-masm-verbose -mconstructor-aliases -fuse-init-array -target-cpu z13
-momit-leaf-frame-pointer -v -dwarf-column-info -debugger-tuning=gdb  -O3
-ferror-limit 19 -fmessage-length 238 -funroll-loops -fobjc-runtime=gcc
-fdiagnostics-show-option -fcolor-diagnostics -vectorize-loops -vectorize-slp
-o expr.s -x ir ./expr.bc -mllvm -verify-machineinstrs

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