https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83875
Bug ID: 83875
Summary: [feature request] target_clones compatible SIMD
capability/length check
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: roland at rschulz dot eu
Target Milestone: ---
Currently there are two methods to check for SIMD capabilities (e.g. AVX). The
preprocessor defines (e.g. __AVX__) and the builtin __builtin_cpu_supports. The
problem is that neither can be used together with target_clones. One happens
too early (preprocessor) and one too late (runtime). I suggest to add a builtin
function which is constexpr and returns the CPU capabilities of the CPU target
and otherwise works like the existing __builtin_cpu_supports. A possible name
would be __builtin_target_supports.
Even outside of target_clones function, such a builtin would have the advantage
that it would allow replacing preprocessor #if with constexpr if.
Prior to filing the feature request I asked on gcc-help for a solution:
https://gcc.gnu.org/ml/gcc-help/2018-01/msg00057.html . No one had an idea for
a solution with current capabilities, and one other developer voiced interest
in such a feature.
