panic when compiling SHA

[Carter Schonwald]

george, the problem with that is not all targets that ghc support have an
llvm backend. (in fact, one problem I hope to help resolve (not in full
mind you) for 7.10 is that theres a semi disjoint coverage across the
backends)


On Thu, Jan 9, 2014 at 3:08 PM, George Colpitts
<george.colpitts at gmail.com>wrote:

> Does LLVM have the same limitation that its register allocator does not
> reuse spill slots for variables that have disjoint live ranges? If not,
> could the library be compiled with llvm?
>
>
> On Thu, Jan 9, 2014 at 3:17 PM, Adam Wick <awick at galois.com> wrote:
>
>> On Jan 8, 2014, at 2:42 AM, Simon Marlow <marlowsd at gmail.com> wrote:
>>
>> Neither of the register allocators reuse spill slots for variables that
>> have disjoint live ranges, so the fact that we ran out of spill slots is
>> not necessarily indicative of terrible code (but I agree that it's a strong
>> hint).
>>
>>
>> That’s the problem with SHA, then. The implementation (and the spec,
>> really) is essentially a long combination of the form:
>>
>> let x_n5 = small_computation x_n1 x_n2 x_n3 x_n4
>>      x_n6 = small_computation x_n2 x_n3 x_n4 x_n5
>>      …
>>
>> Which has ~70 entries. The actual number of live variables alive at any
>> time should be relatively small, but if slots aren’t getting reused there’s
>> going to be some significant blowup. (To be honest, I had figured — and
>> thought I had validated — that doing it this way would give the compiler
>> the best chance at generating optimal code, but it appears I merely set
>> myself up to hit this limitation several years later.)
>>
>>
>> - Adam
>>
>>
>>
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>>
>
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