[LLVMdev] "ran out of registers during register allocation"

[reed kotler]

It seems like it might be a legitimate complaint from the register 
allocator.

It's trying to get an accumulator (not a general purpose register) and 
the accumulator is 64 bit.

It's using a part of the Mips backend that I have not worked in so I 
have to research this a bit.

The multiply instruction is a pseudo multiply in the mips backend and it 
needs the accumulator which a special register
and there is only one and it has special properties. This may normally 
be getting sorted out by some code which
is not present during fast-isel.



On 01/02/2015 02:41 PM, Philip Reames wrote:
>
> On 01/02/2015 02:24 PM, reed kotler wrote:
>> I'm getting this error in RegAllocFast.cpp in compiling one source 
>> file in test-suite as the result of a new Mips fast-isel patch
>> I was testing.
>>
>> It apparently just generates bad code and continues?
>>
>>   // Nothing we can do. Report an error and keep going with a bad 
>> allocation.
>>   if (MI->isInlineAsm())
>>     MI->emitError("inline assembly requires more registers than 
>> available");
>>   else
>>     MI->emitError("ran out of registers during register allocation");
>>
>>
>> How is it possible to run out of registers during register 
>> allocation? Lol.
> This seems to be one of the more common errors when you get a MI 
> instruction definition wrong.  In particular, I saw this a lot when 
> experimenting with various lowering strategies for the statepoint 
> work.  I'd suggest trying to reduce the example using bugpoint and 
> looking closely at the machine instructions.
>>
>> Reed
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>