[llvm-bugs] [Bug 40504] New: LLVM should model TLSDESC accessor as clobbering NZCV

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=40504

            Bug ID: 40504
           Summary: LLVM should model TLSDESC accessor as clobbering NZCV
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Backend: AArch64
          Assignee: unassignedbugs at nondot.org
          Reporter: peter at pcc.me.uk
                CC: arnaud.degrandmaison at arm.com,
                    llvm-bugs at lists.llvm.org, peter.smith at linaro.org,
                    Ties.Stuij at arm.com

While reviewing Android's proposed implementation of TLSDESC:
https://android-review.googlesource.com/c/platform/bionic/+/886118

I noticed that it does not attempt to preserve NZCV. LLVM's model of TLSDESC,
on the other hand, assumes that NZCV is preserved:
http://llvm-cs.pcc.me.uk/lib/Target/AArch64/AArch64InstrInfo.td#1639

glibc's implementation of TLSDESC doesn't look like it attempts to preserve
NZCV either:
https://github.com/bminor/glibc/blob/e1e47c912a8e557508362715f7468091def3ec4f/sysdeps/aarch64/dl-tlsdesc.S

I think that what this means is that we should add NZCV to the list of clobbers
for the TLSDESC accessor.

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