llvm dev - Dec 2012 - [LLVMdev] alignment issue, getting corrupt double values

On 31/12/12 19:47, Joe Groff wrote:
>  I think most backends treat struct return by value as returning
> multiple values in registers; for instance, {i32, i64} returns into
> {EAX, RDX} on x86-64. Since most architectures don't specify any more
> than two return registers and you can't really "spill" a
return value,
> weird poorly-tested things probably happen if you try to return a struct
> with more elements than the backend has return registers for. You could
> try returning larger structs indirectly using an sret pointer like Clang
> does.
I do pass the return as the first parameter pointer now. I didn't know
about sret, I guess I should mark it is as such (does it help
optimization then?)

I also think it is kind of dangerous that LLVM silently accepts returns
of larger structures and then produces invalid code.  Note that it does
actually pass by pointer if the backend can't return it directly, just
in certain cases it fails to produce correct code.

-- 
edA-qa mort-ora-y
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On Monday, December 31, 2012, edA-qa mort-ora-y wrote:

> I also think it is kind of dangerous that LLVM silently accepts returns
> of larger structures and then produces invalid code.  Note that it does
> actually pass by pointer if the backend can't return it directly, just
> in certain cases it fails to produce correct code.

You should definitely file a bug. Did you build LLVM with assertions
enabled? If not, try rebuilding with assertions, and you might get an
indication of what's breaking instead of silent bad behavior.

-Joe
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On 01/01/13 00:52, Joe Groff wrote:
> You should definitely file a bug. Did you build LLVM with assertions
> enabled? If not, try rebuilding with assertions, and you might get an
> indication of what's breaking instead of silent bad behavior.
Yes, assertions are enabled: I get them all the time, just not here. ;)

I'll file a defect.


-- 
edA-qa mort-ora-y
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