llvm dev - Jul 2009 - [LLVMdev] Alloca with LLVMContext

Dear All,

Is there a reason why the AllocaInst constructor takes an LLVMContext
argument?  Can't it just determine the context from either the basic
block or instruction pointer argument?

If the constructor can infer the context automatically, that would save
one API change.

If the constructor can't infer it, would it be possible to make the
context the last parameter and have it use a default LLVMContext (say,
the one from getGlobalContext())?

Either of these would ease the transition effort.

-- John T.

On Jul 15, 2009, at 8:14 AM, John Criswell wrote:
> Dear All,
>
> Is there a reason why the AllocaInst constructor takes an LLVMContext
> argument?  Can't it just determine the context from either the basic
> block or instruction pointer argument?
BasicBlocks and Instructions don't necessarily have contexts, if  
they're not attached to a module.  You can also construct an  
AllocaInst without attaching it to a BasicBlock.

This problem was simpler for global values, where they're attached  
directly to a Module, which must have a context.  There I was able to  
split it into constructors that take mandatory contexts and ones that  
take mandatory modules.  With Instructions, it doesn't work so well,  
because even if I make the BasicBlock mandatory, there is not  
guarantee that it is attached to a Module.

This could be an argument for pushing the context member does into BBs  
and Instructions, but that has performance and memory use implications  
that I haven't considered yet.
> If the constructor can't infer it, would it be possible to make the
> context the last parameter and have it use a default LLVMContext (say,
> the one from getGlobalContext())?
Possibly.  I'll look at it when I get in.

--Owen
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On Wed, Jul 15, 2009 at 8:52 AM, Owen Anderson<resistor at mac.com>
wrote:
>
> On Jul 15, 2009, at 8:14 AM, John Criswell wrote:
>
> Dear All,
>
> Is there a reason why the AllocaInst constructor takes an LLVMContext
> argument?  Can't it just determine the context from either the basic
> block or instruction pointer argument?
>
> BasicBlocks and Instructions don't necessarily have contexts, if
they're not
> attached to a module.  You can also construct an AllocaInst without
> attaching it to a BasicBlock.
I must have missed something. I think you've said that all Types will
have a Context, in which case the AllocaInst could pull the context
from its type.

Jeffrey