https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112600
--- Comment #14 from GCC Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Uros Bizjak <u...@gcc.gnu.org>: https://gcc.gnu.org/g:8bb6b2f4ae19c3aab7d7a5e5c8f5965f89d90e01 commit r15-1122-g8bb6b2f4ae19c3aab7d7a5e5c8f5965f89d90e01 Author: Uros Bizjak <ubiz...@gmail.com> Date: Sun Jun 9 12:09:13 2024 +0200 i386: Implement .SAT_SUB for unsigned scalar integers [PR112600] The following testcase: unsigned sub_sat (unsigned x, unsigned y) { unsigned res; res = x - y; res &= -(x >= y); return res; } currently compiles (-O2) to: sub_sat: movl %edi, %edx xorl %eax, %eax subl %esi, %edx cmpl %esi, %edi setnb %al negl %eax andl %edx, %eax ret We can expand through ussub{m}3 optab to use carry flag from the subtraction and generate code using SBB instruction implementing: unsigned res = x - y; res &= ~(-(x < y)); sub_sat: subl %esi, %edi sbbl %eax, %eax notl %eax andl %edi, %eax ret PR target/112600 gcc/ChangeLog: * config/i386/i386.md (ussub<mode>3): New expander. (sub<mode>_3): Ditto. gcc/testsuite/ChangeLog: * gcc.target/i386/pr112600-b.c: New test.
