Hello, Qing, It was a pleasure to meet you at the Cauldron.
On Oct 21, 2022, Qing Zhao <qing.z...@oracle.com> wrote: > Hi, Alexandre, > Could you please explain a little bit on the motivation of this patch first? It was a suggestion I got after the Cauldron presentation. It made sense to me, and was easy enough to implement. 'all' for leaf functions is likely wasteful. If no other functions are called, one can determine exactly which registers might carry information out and thus need zeroing, and 'used' is thus likely enough, depending on the purpose of register scrubbing. (In some scenarios, it might make sense to want scrubbing of all registers, even unused ones that carry incoming values) Though some functions are coded as leaf functions, others may become leaf functions because of inlining or other optimizations. It's hard for users to predict, so it makes sense to have a mode that tells the compiler to figure it out. There's room for a follow-up improvement, to save on a little more potentially-wasteful anti-leaking scrubbing even in non-leaf functions: for this purpose, they need not scrub registers that they don't use themselves, if all potential callees are known to have scrubbed them. I have not (yet?) implemented this variant; I haven't even found a name I'm happy with for it. (seal? plug? cork? another leak antonym?) I'm not entirely happy with leafy either, FWIW. Bikeshedding anyone? :-) https://gcc.gnu.org/pipermail/gcc-patches/2022-October/604083.html -- Alexandre Oliva, happy hacker https://FSFLA.org/blogs/lxo/ Free Software Activist GNU Toolchain Engineer Disinformation flourishes because many people care deeply about injustice but very few check the facts. Ask me about <https://stallmansupport.org>
