[libc] abs is a const function

[AtariDreams]

No description provided.

[llvmbot]

@llvm/pr-subscribers-libc

Author: AtariDreams (AtariDreams)

Changes

---

Full diff: https://github.com/llvm/llvm-project/pull/79650.diff

1 Files Affected:

• (modified) libc/src/stdlib/abs.h (+1-1)

diff --git a/libc/src/stdlib/abs.h b/libc/src/stdlib/abs.h
index 19cef1446bd36df..ccfdccf2024a9e7 100644
--- a/libc/src/stdlib/abs.h
+++ b/libc/src/stdlib/abs.h
@@ -11,7 +11,7 @@
 
 namespace LIBC_NAMESPACE {
 
-int abs(int n);
+int __attribute__((__const__)) abs(int n);
 
 } // namespace LIBC_NAMESPACE
 

[jhuber6]

@michaelrj-google Do we have a formalized way to specify attributes? My gut says it should go in libc/spec/stdc.td but I remember hearing there was some desire to move away from tablegen?

[AtariDreams]

@michaelrj-google Do we have a formalized way to specify attributes? My gut says it should go in libc/spec/stdc.td but I remember hearing there was some desire to move away from tablegen?

I have no idea how to do it in tablegen

[jhuber6]

As it stands, this won't be exported. The header modified is simply the internal header. The installed ones go through a tool called lib-hdrgen which uses LLVM TableGen to spit the definitions out into where %%public_api() is.

[jhuber6]

I have no idea how to do it in tablegen

I was asking Michael, because I recall that this is an existing issue that the infrastructure hasn't solved yet. I had problems earlier where it conflicted with a lot of GNU definitions that expect things like pure or similar.

[SchrodingerZhu]

We have internal versions of math kernels inside LIBC_NAMESPACE. I think it is legitimate to add additional attributes to these internal versions of these functions if found helpful (improving codegen of other internal functions). Adding non-standard attributes to the exposed version as specified in spec.td sometimes will lead to problems.

[SchrodingerZhu]

This approval is to dismiss previous "Request changes". I don't know how to dismiss a "Request changes" without approving the PR.

[nickdesaulniers]

Isn't #79891 trying to add generalized support for attributes?

[jhuber6]

Isn't #79891 trying to add generalized support for attributes?

I think the attributes on the installed headers and the internal headers are separate.