Function calls between methods with the same __attribute__((target)) are not resolved to the target-specific clone

[DaMatrix]

Godbolt example

In the following example:

__attribute__((target("default")))
static int ctz(unsigned i) { return __builtin_ctz(i); }

__attribute__((target("arch=skylake")))
static int ctz(unsigned i) { return __builtin_ctz(i); }

__attribute__((target("default")))
int indirect_ctz(unsigned i) { return ctz(i); }

__attribute__((target("arch=skylake")))
int indirect_ctz(unsigned i) { return ctz(i); }

I would expect that indirect_ctz [default] and indirect_ctz [clone .arch_skylake] would be able to be optimized into static calls to ctz [default] and ctz [clone .arch_skylake], respectively. As can be seen on the Godbolt link above, GCC is able to perform this optimization (and then inline them). However, with clang both of the indirect_ctz versions simply call the ifunc-resolved version of ctz, which prevents inlining optimizations from taking effect.

Additionally, it seems that clang is also not able to perform this optimization if __attribute__((target_clones)) is used for either one or both of ctz or indirect_ctz:
Example 1
Example 2
Example 3
(GCC is able to optimize it into a static call to the target-specific implementation in examples 2 and 3, but fails to inline)

[jroelofs]

related: #71714