[llvm-bugs] [Bug 44445] New: [X86] Regcall calling convention mismanaged X87 fp stack if long double is an input argument but is never used

via llvm-bugs llvm-bugs at lists.llvm.org
Thu Jan 2 10:45:45 PST 2020


https://bugs.llvm.org/show_bug.cgi?id=44445

            Bug ID: 44445
           Summary: [X86] Regcall calling convention mismanaged X87 fp
                    stack if long double is an input argument but is never
                    used
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Windows NT
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Backend: X86
          Assignee: unassignedbugs at nondot.org
          Reporter: craig.topper at gmail.com
                CC: craig.topper at gmail.com, llvm-bugs at lists.llvm.org,
                    llvm-dev at redking.me.uk, spatel+llvm at rotateright.com

The regcall calling convention allows long double to be passed into a function
in ST0. The called function is responsible for removing this data from the x87
stack when it is done with it.

This works if the argument is used in the function since it appears in the
function livein list so the FP stackifier will see it and remove it when its
done with it.

But if the argument is never used, then its not in the livein list so the FP
stackifier doesn't see it and doesn't remove it.

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