Re: RFC: Patch to allow spill slot alignment greater than the stack alignment

[Steve Ellcey <sellcey@imgtec.com>]

On Tue, 2015-10-06 at 17:39 +0200, Bernd Schmidt wrote:

> 
> Did your tag that copy as RTX_FRAME_RELATED? I'd expect dwarf2cfi would 
> ignore instructions with that bit unset. There's even a comment 
> indicating arm does something like this:

Yes, I had marked it as RTX_FRAME_RELATED.  When I took that out things
looked better (well, maybe just different).

If I remove that and I change Rule #16 to handle an AND with a register
I get odd looking .cfi stuff.  The AND instruction (which is marked with
RTX_FRAME_RELATED) seems to generate these cfi_escape macros:

	.cfi_escape 0x10,0x1f,0x2,0x8e,0x7c
	.cfi_escape 0x10,0x1e,0x2,0x8e,0x78
	.cfi_escape 0x10,0xc,0x2,0x8e,0x74

which are meaningless to me.  What I found works better is to skip the
dwarf2cfi.c changes and explicitly attach this note to the AND
instruction:

      cfi_note = alloc_reg_note (REG_CFA_DEF_CFA, stack_pointer_rtx, NULL_RTX);
      REG_NOTES (insn) = cfi_note;

When I do this the only unexpected test suite execution failures I see
are ones that call the C++ set_unexpected function.

FYI: The reason I was copying the stack pointer to another register was
to use that other register as my argument pointer (needed after the
stack pointer got aligned) and to use it to restore the stack pointer at
the end of the function for normal returns.

Steve Ellcey
sellcey@imgtec.com