llvm dev - Sep 2008 - [LLVMdev] BUILD_TRIPLET node.

Currently I can use a BUILD_PAIR to make a pair of two arbitrary values
to a desired result value. For example, I can make   i8,build_pair (i8, i8)  or
i16,build_pair = (i1, i8).

This is turning out to very handy when I replace nodes during the
expansion/legalization of types for my target.

I was just wondering if we could go one more step further and create a
BUILD_TRIPLET node which can contain three incoming operands instead of
just two.  I know that I can do that with two build_pairs , but a
build_triplet will make my code cleaner and easy to follow.

- Sanjiv

On Mon, Sep 1, 2008 at 10:50 AM, sanjiv gupta
<sanjiv.gupta at microchip.com> wrote:
> Currently I can use a BUILD_PAIR to make a pair of two arbitrary values
> to a desired result value. For example, I can make   i8,build_pair >
(i8, i8)  or i16,build_pair = (i1, i8).
I don't think those are legal; from SelectionDAGNodes.h:

    // BUILD_PAIR - This is the opposite of EXTRACT_ELEMENT in some ways.  Given
    // two values of the same integer value type, this produces a value twice as
    // big.  Like EXTRACT_ELEMENT, this can only be used before legalization.
> This is turning out to very handy when I replace nodes during the
> expansion/legalization of types for my target.
>
> I was just wondering if we could go one more step further and create a
> BUILD_TRIPLET node which can contain three incoming operands instead of
> just two.  I know that I can do that with two build_pairs , but a
> build_triplet will make my code cleaner and easy to follow.
Maybe MERGE_VALUES would be more suited to what you're doing?

-Eli

On Sep 1, 2008, at 10:50 AM, sanjiv gupta wrote:
> Currently I can use a BUILD_PAIR to make a pair of two arbitrary  
> values
> to a desired result value. For example, I can make   i8,build_pair >
(i8, i8)  or i16,build_pair = (i1, i8).
>
> This is turning out to very handy when I replace nodes during the
> expansion/legalization of types for my target.
>
> I was just wondering if we could go one more step further and create a
> BUILD_TRIPLET node which can contain three incoming operands instead  
> of
> just two.  I know that I can do that with two build_pairs , but a
> build_triplet will make my code cleaner and easy to follow.
We generally do not extend the IR just for convenience. Adding  
something like BUILD_TRIPLET is too arbitrary. It goes against the  
LLVM philosophy. Sorry.

Evan
>
>
> - Sanjiv
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