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Re: fake/abnormal/eh edge question

On Tue, 2015-08-25 at 14:44 -0600, Jeff Law wrote:

> > I want to preserve the copy of $sp to $12 and I also want to preserve the
> > .cfi psuedo-ops (and code) in the exit block and epilogue in order for
> > exception handling to work correctly.  One way I thought of doing this
> > is to create an edge from the entry block to the exit block but I am
> > unsure of all the implications of creating a fake/eh/abnormal edge to
> > do this and which I would want to use.
> Presumably it's the RTL DCE pass that's eliminating this stuff?

Actually, it looks like is peephole2 that is eliminating the
instructions (and .cfi psuedo-ops).

> Do you have the FRAME_RELATED bit set of those insns?
> But what I don't understand is why preserving the code is useful if it 
> can't be reached.  Maybe there's something about the dwarf2 unwinding 
> that I simply don't understand -- I've managed to avoid learning about 
> it for years.

I am not entirely sure I need the code or if I just need the .cfi
psuedo-ops and that I need the code to generate the .cfi stuff.

I wish I could avoid the dwarf unwinder but that seems to be the main
problem I am having with stack realignment.  Getting the cfi stuff right
so that the unwinder works properly is proving very hard.

Steve Ellcey

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