[LLVMdev] variable size alloca

[John Criswell]

Ryan M. Lefever wrote:
> To what do variable size LLVM alloca instructions get translated, when
> they are turned into machine code?  I compiled a piece of code to
> bitcode and disassembled it.  The disassembled code showed that there
> were alloca instructions with variable-sized parameters within the
> bitcode.  When I turned the bitcode into machine code, I performed an nm
> on the result but didn't see any symbols referring to alloca.  So, I'm
> guessing that they don't get translated to an alloca system call.  If
> that's the case, to what do they get translated?
>   
It's been a long time since I've looked at machine code generated by 
LLVM, but if I had to guess, I think it should be lowered into an 
instruction that adjusts the stack pointer.  All alloca does is allocate 
stack space; an adjustment of the stack pointer (on x86, decreasing it) 
should suffice once the size of the allocation has been computed.

-- John T.

> Regards,
> Ryan
>
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