[llvm-dev] Dealing with boolean values in GlobalISel

[Nicolai Hähnle-Montoro via llvm-dev]

On Fri, Sep 27, 2019 at 9:47 PM Arsenault, Matthew via llvm-dev
<llvm-dev at lists.llvm.org> wrote:
> define i32 @foo(i32 %a, i32 %b, i32 %c) {
>   %cc = trunc i32 %a to i1
>   %r = select i1 %cc, i32 %b, i32 %c
>   ret i32 %r
> }
[snip]
> Can we make truncates to s1 illegal? [...]

You're saying that in the example above, we'd first generate a G_TRUNC
to s1, which would then be legalized to a compare against 0 (which has
an s1 result)?

That actually seems quite reasonable to me.

What if the program has an s32 input value which is known for whatever
reason to be either 0 or 1? In that case, we may still want to be able
to convert the value to an s1 with a no-op operation. Any idea how
that would be represented?

Cheers,
Nicolai


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> -Matt
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