On 2014-06-11, 1:17 PM, Chung-Lin Tang wrote: > On 2014/6/11 下午 06:32, James Greenhalgh wrote: >> >> Hi, >> >> A recent change somewhere exposed a latent bug between LRA and the definition >> of the movsi_compare0 pattern. >> >> This pattern ties the source and destination register of a set together >> a (match_dup) and register constraints: >> >> [(set (reg:CC CC_REGNUM) >> (compare:CC (match_operand:SI 1 "s_register_operand" "0,r") >> (const_int 0))) >> (set (match_operand:SI 0 "s_register_operand" "=r,r") >> (match_dup 1))] >> >> This confuses LRA which expects the source and destination register of >> a set to be different. >> >> reduced.c: In function '_IO_vfscanf_internal': >> reduced.c:104:1: internal compiler error: in lra_create_copy, at lra.c:1512 >> } >> ^ >> 0x8c3f9a lra_create_copy(int, int, int) >> /work/gcc-dev/src/gcc/gcc/lra.c:1512 >> 0x8e4ab0 process_bb_lives >> /work/gcc-dev/src/gcc/gcc/lra-lives.c:568 >> 0x8e4ab0 lra_create_live_ranges(bool) >> /work/gcc-dev/src/gcc/gcc/lra-lives.c:1019 >> 0x8c5a39 lra(_IO_FILE*) >> /work/gcc-dev/src/gcc/gcc/lra.c:2356 >> 0x873a96 do_reload >> /work/gcc-dev/src/gcc/gcc/ira.c:5415 >> 0x873a96 execute >> /work/gcc-dev/src/gcc/gcc/ira.c:5576 >> Please submit a full bug report, >> >> We can fix the pattern by moving away from match_dup and using register >> tying with constraints consistently. >> >> I'm not entirely convinced that this is legitimate (my vague recollection is >> that register tying should only be used to tie inputs to outputs). >> >> This has passed testing on a bunch of ARM targets, and fixes the build >> issues I've been seeing. > > Looking at this too, as an LRA exercise. I don't really think the > pattern is wrong, rather LRA should just avoid creating the copy in this > case; it's a result of operand constraining, after all. > > Attached is the small LRA patch, pending testing. Vladimir should weight > in on this. >
The patch is safe and ok. Thanks for working on it, Chung-Lin. > * ira-lives.c (process_bb_lives): Skip creating copy during > insn sca when src/dest has constrained to same regno. >
