llvm dev - Oct 2010 - [LLVMdev] Re : How to assign a constant to a register?

leledumbo,

from what you say, I assume you have some kind of representation (AST or a 
lower-level intermediate representation) from which you generate LLVM assembly.
Is this representation in SSA form?
If it is, you might want to do a "copy propagation" transformation
that replaces
the uses of all variables that are assigned a constant value by their 
definitions.
Example:

x = 5
y = x + 1
z = x * y

becomes

y = 5 + 1
z = 5 * y

Cheers
Matthieu



----- Message d'origine ----
> De : Duncan Sands <baldrick at free.fr>
> À : llvmdev at cs.uiuc.edu
> Envoyé le : Mer 20 octobre 2010, 11h 59min 32s
> Objet : Re: [LLVMdev] How to assign a constant to a register?
> 
> On 20/10/10 11:37, leledumbo wrote:
> >
> >> Why not just use  ConstantInt::get() when you want the number 5?
> >
> > Because I'm not  using LLVM libraries, I'm generating LLVM
assembly myself.
> 
> In that case,  why not output '5' when you want  5?
> 
> Ciao,
> 
> Duncan.
> _______________________________________________
> LLVM  Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
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>

Hi,

If x is a local variable, it will be stored on the stack. So you need an
alloca for it:

%x = alloca i8    ; <i8*>

Then you can just perform a store:

Store i8* %x, i8 0

Cheers,

James
> -----Original Message-----
> From: llvmdev-bounces at cs.uiuc.edu [mailto:llvmdev-bounces at
cs.uiuc.edu]
> On Behalf Of leledumbo
> Sent: 20 October 2010 14:39
> To: llvmdev at cs.uiuc.edu
> Subject: Re: [LLVMdev] Re : How to assign a constant to a register?
> 
> 
> > from what you say, I assume you have some kind of representation
(AST
> or a
> > lower-level intermediate representation) from which you generate
LLVM
> > assembly.
> > Is this representation in SSA form?
> 
> Yes, the representation is an AST. It's not in SSA yet, as it's a
> direct
> representation of the input. I'm confused for this node:
>   :>  /  \
> x    0
> 
> where x is a local variable.
> 
> > If it is, you might want to do a "copy propagation"
transformation
> that
> > replaces
> > the uses of all variables that are assigned a constant value by
their
> > definitions.
> 
> I'll consider it, it would useful for constant expression.
> 
> --
> View this message in context: http://old.nabble.com/How-to-assign-a-
> constant-to-a-register--tp29987387p30009972.html
> Sent from the LLVM - Dev mailing list archive at Nabble.com.
> 
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