https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94795
--- Comment #5 from CVS 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:9decd08b7b153a593a0b61e4f5373cb9574a1973 commit r11-45-g9decd08b7b153a593a0b61e4f5373cb9574a1973 Author: Uros Bizjak <ubiz...@gmail.com> Date: Mon May 4 18:53:30 2020 +0200 i386: Use SBB more [PR94650] When returning 0 or -1, "SBB reg,reg" instruction that borrows carry flag can be used. Carry flag can be generated by converting compare with zero to a LTU compare with one, so e.g. return -(x == 0) generates: cmpq $1, %rdi sbbq %rax, %rax instead of: xorl %eax, %eax testq %rdi, %rdi sete %al negq %rax A similar conversion can be used for return -(x != 0) where NEG insn can be used instead of compare. According to x86 ISA, NEG insn sets carry flag when the source operand is != 0, resulting in: negq %rdi sbbq %rax, %rax The conversion avoids partial register stall with SETcc instructions. PR target/94795 * config/i386/i386.md (*neg<mode>_ccc): New insn pattern. (EQ compare->LTU compare splitter): New splitter. (NE compare->NEG splitter): Ditto. testsuite/ChangeLog: PR target/94795 * gcc.target/i386/pr94795-1.c: New test. * gcc.target/i386/pr94795-2.c: New test.
