Hi Roger, The patch looks sane. Have you run dejagnu test suite?
Thanks, Claudiu -----Original Message----- From: Roger Sayle <ro...@nextmovesoftware.com> Sent: Friday, September 29, 2023 6:54 PM To: gcc-patches@gcc.gnu.org Cc: Claudiu Zissulescu <claz...@synopsys.com> Subject: [ARC PATCH] Use rlc r0,0 to implement scc_ltu (i.e. carry_flag ? 1 : 0) This patch teaches the ARC backend that the contents of the carry flag can be placed in an integer register conveniently using the "rlc rX,0" instruction, which is a rotate-left-through-carry using zero as a source. This is a convenient special case for the LTU form of the scc pattern. unsigned int foo(unsigned int x, unsigned int y) { return (x+y) < x; } With -O2 -mcpu=em this is currently compiled to: foo: add.f 0,r0,r1 mov_s r0,1 ;3 j_s.d [blink] mov.hs r0,0 [which after an addition to set the carry flag, sets r0 to 1, followed by a conditional assignment of r0 to zero if the carry flag is clear]. With the new define_insn/optimization in this patch, this becomes: foo: add.f 0,r0,r1 j_s.d [blink] rlc r0,0 This define_insn is also a useful building block for implementing shifts and rotates. Tested on a cross-compiler to arc-linux (hosted on x86_64-pc-linux-gnu), and a partial tool chain, where the new case passes and there are no new regressions. Ok for mainline? 2023-09-29 Roger Sayle <ro...@nextmovesoftware.com> gcc/ChangeLog * config/arc/arc.md (CC_ltu): New mode iterator for CC and CC_C. (scc_ltu_<mode>): New define_insn to handle LTU form of scc_insn. (*scc_insn): Don't split to a conditional move sequence for LTU. gcc/testsuite/ChangeLog * gcc.target/arc/scc-ltu.c: New test case. Thanks in advance, Roger --