[llvm-bugs] [Bug 31346] New: Investigate whether or not we need a frame pointer

[via llvm-bugs]

https://llvm.org/bugs/show_bug.cgi?id=31346

            Bug ID: 31346
           Summary: Investigate whether or not we need a frame pointer
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: All
            Status: NEW
          Severity: normal
          Priority: P
         Component: Backend: AVR
          Assignee: unassignedbugs at nondot.org
          Reporter: dylanmckay34 at gmail.com
                CC: llvm-bugs at lists.llvm.org
    Classification: Unclassified

In the past, we removed the frame pointer (R29R28). The code made the
assumption that the register would always contain the frame pointer.

If you look at the AVR-GCC wiki, it will always set up a frame pointer

https://gcc.gnu.org/wiki/avr-gcc

> In order to access stack locations, avr-gcc will set up a 16-bit frame pointer in R29:R28 (Y) because the stack pointer (SP) cannot be used to access stack slots. 

We may need to add this back in in order to be compatible with the AVR-GCC
calling convention.

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