llvm dev - Oct 2010 - [LLVMdev] Re : 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.

> In that case, why not output '5' when you want 5?
Like I said before, I'm used to common assembly language like x86. Usually I
assign an initial value to a register, then manipulate it.
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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
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>

> 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.

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