[PATCH] D61634: [clang/llvm] Allow efficient implementation of libc's memory functions in C/C++

Thu May 23 22:00:42 PDT 2019

tejohnson added a comment.

In D61634#1512020 <https://reviews.llvm.org/D61634#1512020>, @gchatelet wrote:

> AFAIU here is a coarse plan of what needs to happen
>
> 1. Add a `no-builtin` clang function attribute that has the same semantic as the `no-builtin` cmd line argument <https://clang.llvm.org/docs/ClangCommandLineReference.html#cmdoption-clang-fbuiltin>
> 2. Propagate it to the IR.
>   - In the light of recent discussions and as @theraven suggested it seems more appropriate to encode them as individual IR attributes (e.g. `"no-builtin-memcpy"`, `"no-builtin-sqrt"`, etc..)
> 3. Propagate/merge the `no-builtin` IR attribute for LTO by "updating `AttributeFuncs::areInlineCompatible` and/or `AttributeFuncs::mergeAttributesForInlining` and adding a new MergeRule in `include/llvm/IR/Attributes.td` and writing a function like `adjustCallerStackProbeSize`."

This one isn't about LTO, but rather the inliner. You could have different functions in the same module even without LTO that have incompatible no-builtin attributes. There isn't any propagation required for LTO.

> 4. Get inspiration from `TargetTransformInfo` to get `TargetLibraryInfo` on a per function basis for all passes and respect the IR attribute.
> 
>   I'm not familiar with 3 and 4 but I can definitely have a look. I'll update this patch to do 1 and 2 in the meantime. @tejohnson let me know how you want to proceed for your related patch <https://reviews.llvm.org/D60162>. I'm happy to help if I can.

I will mark that one obsolete. I can work on 4, it may just take some time to get it all plumbed.

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