On Mon, Mar 02, 2020 at 09:13:53AM -0800, Ryan Libby wrote: > On Mon, Mar 2, 2020 at 12:45 AM Alexander V. Chernikov <melif...@ipfw.ru> > wrote: > > > > 28.02.2020, 18:32, "Ryan Libby" <rli...@freebsd.org>: > > > Author: rlibby > > > Date: Fri Feb 28 18:32:36 2020 > > > New Revision: 358439 > > > URL: https://svnweb.freebsd.org/changeset/base/358439 > > > > > > Log: > > > amd64 atomic.h: minor codegen optimization in flag access > > > > > > Previously the pattern to extract status flags from inline assembly > > > blocks was to use setcc in the block to write the flag to a register. > > > This was suboptimal in a few ways: > > > - It would lead to code like: sete %cl; test %cl; jne, i.e. a flag > > > would just be loaded into a register and then reloaded to a flag. > > > - The setcc would force the block to use an additional register. > > > - If the client code didn't care for the flag value then the setcc > > > would be entirely pointless but could not be eliminated by the > > > optimizer. > > > > > > A more modern inline asm construct (since gcc 6 and clang 9) allows for > > This effectively restricts kernel builds by all older compilers. > > Is there any chance of making it conditional depending on the compiler > > version/features? What is the older compiler you need to use for base system ? And why ?
> > Yes, it is possible to test for __GCC_ASM_FLAG_OUTPUTS__. It is more > maintenance effort going forward. If building current with an old cross > compiler is an important scenario, we can either revert this and the > following revision or work up a patch to make it conditional. I'll see > what that might look like. _______________________________________________ svn-src-head@freebsd.org mailing list https://lists.freebsd.org/mailman/listinfo/svn-src-head To unsubscribe, send any mail to "svn-src-head-unsubscr...@freebsd.org"
