Re: GCC used to store pointers in FP registers on aarch64

2025-03-28 Thread Attila Szegedi via Gcc
Hey folks, My colleague Nicolas Savoire created a compiler reproducer[0] for the effect -- you can see a side-by-side comparison of code compiled with GCC 8.x and 9.x where 8.x emits fmov instructions and 9.x does not. He further used this example as a git bisect criteria and eventually found the

Re: GCC used to store pointers in FP registers on aarch64

2025-02-24 Thread Attila Szegedi via Gcc
On Mon, Feb 24, 2025 at 1:21 PM Florian Weimer wrote: > * Attila Szegedi: > > >> That seems … quite unlikely. GCC 8 has seen extensive use on > >> AArch64, on a variety of implementations, and I don't recall > >> problems in this area. I don't follow AArch64 *that* closely, > >> admittedly, but

Re: GCC used to store pointers in FP registers on aarch64

2025-02-24 Thread Attila Szegedi via Gcc
On Mon, Feb 24, 2025 at 12:41 PM Florian Weimer wrote: > > Surely not preserving floating point bit patterns in registers would > be a silicon bug? Indeed it would be. > That seems … quite unlikely. GCC 8 has seen > extensive use on AArch64, on a variety of implementations, and I don't > rec

GCC used to store pointers in FP registers on aarch64

2025-02-24 Thread Attila Szegedi via Gcc
Hi folks, I'm looking for a bit of a historic context for a fun GCC behavior we stumbled across. For... reasons we build some of our binaries using an older version of GCC (8.3.1, yes, we'll be upgrading soon, and no, this message is not about helping with an ancient version :-) ) We noticed that