Re: Patches to fix optimizer bug & C++ exceptions for GCC VAX backend

[Jeff Law <law%redhat.com@localhost>]

On 04/01/2016 01:06 PM, Jake Hamby wrote:
> My theory is that it has to do with liveness detection and a write
> into the stack frame being incorrectly seen as updating a local
> variable, but that could be completely wrong. I was hoping that by
> cc'ing gcc-patches that somebody more familiar with why some phase of
> the optimizer might decide to delete this particular insn that copies
> data into the stack (to overwrite the return address, e.g. to move to
> EH_RETURN_HANDLER_RTX) immediately before returning.
Dead store elimination is the most likely candidate.  It "knows" that 
stores into the local frame are dead when the function returns and uses 
that information to eliminate such stores.

You may just need to set the volatile flag on the MEM when you generate 
it in your backend.  For example see 
config/pa/pa.c::pa_eh_return_handler_rtx.

Jeff