[llvm-bugs] [Bug 42966] New: Regression(r365860) New fomit-frame-pointer / momit-leaf-frame-pointer handling leads to unfriendly diagnostics

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https://bugs.llvm.org/show_bug.cgi?id=42966

            Bug ID: 42966
           Summary: Regression(r365860) New fomit-frame-pointer /
                    momit-leaf-frame-pointer handling leads to unfriendly
                    diagnostics
           Product: clang
           Version: trunk
          Hardware: PC
                OS: All
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: C
          Assignee: unassignedclangbugs at nondot.org
          Reporter: nicolasweber at gmx.de
                CC: blitzrakete at gmail.com, dgregor at apple.com,
                    erik.pilkington at gmail.com, llvm-bugs at lists.llvm.org,
                    richard-llvm at metafoo.co.uk

Say you want frame pointers but no leaf frame pointers (because you want to
unwind, but including leaf frame pointers makes llvm run out of registers -- cf
PR15798).

So you pass -fno-omit-frame-pointer -momit-leaf-frame-pointer to all compiles.


Some specific translation unit wants to omit frame pointers for some reason
though, so it tacks on fomit-frame-pointer. Previously that worked fine.

Now it results in

clang: warning: argument unused during compilation: '-momit-leaf-frame-pointer'
[-Wunused-command-line-argument]

That's true, but it's also not helpful. There's no good way in practice to fix
this warning if it arises in a situation like this.

We should probably manually claim the momit flags if the fomit flags are seen.

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