https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87763
--- Comment #63 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Richard Sandiford <rsand...@gcc.gnu.org>: https://gcc.gnu.org/g:465c7c89e92a6d6d582173e505cb16dcb9873034 commit r10-6283-g465c7c89e92a6d6d582173e505cb16dcb9873034 Author: Richard Sandiford <richard.sandif...@arm.com> Date: Sun Jan 26 13:01:48 2020 +0000 simplify-rtx: Extend (truncate (*extract ...)) fold [PR87763] In the gcc.target/aarch64/lsl_asr_sbfiz.c part of this PR, we have: Failed to match this instruction: (set (reg:SI 95) (ashift:SI (subreg:SI (sign_extract:DI (subreg:DI (reg:SI 97) 0) (const_int 3 [0x3]) (const_int 0 [0])) 0) (const_int 19 [0x13]))) If we perform the natural simplification to: (set (reg:SI 95) (ashift:SI (sign_extract:SI (reg:SI 97) (const_int 3 [0x3]) (const_int 0 [0])) 0) (const_int 19 [0x13]))) then the pattern matches. And it turns out that we do have a simplification like that already, but it would only kick in for extractions from a reg, not a subreg. E.g.: (set (reg:SI 95) (ashift:SI (subreg:SI (sign_extract:DI (reg:DI X) (const_int 3 [0x3]) (const_int 0 [0])) 0) (const_int 19 [0x13]))) would simplify to: (set (reg:SI 95) (ashift:SI (sign_extract:SI (subreg:SI (reg:DI X) 0) (const_int 3 [0x3]) (const_int 0 [0])) 0) (const_int 19 [0x13]))) IMO the subreg case is even more obviously a simplification than the bare reg case, since the net effect is to remove either one or two subregs, rather than simply change the position of a subreg/truncation. However, doing that regressed gcc.dg/tree-ssa/pr64910-2.c for -m32 on x86_64-linux-gnu, because we could then simplify a :HI zero_extract to a :QI one. The associated *testqi_ext_3 pattern did already seem to want to handle QImode extractions: "ix86_match_ccmode (insn, CCNOmode) && ((TARGET_64BIT && GET_MODE (operands[2]) == DImode) || GET_MODE (operands[2]) == SImode || GET_MODE (operands[2]) == HImode || GET_MODE (operands[2]) == QImode) but I'm not sure how often the QI case would trigger in practice, since the zero_extract mode was restricted to HI and above. I checked the other x86 patterns and couldn't see any other instances of this. 2020-01-28 Richard Sandiford <richard.sandif...@arm.com> gcc/ PR rtl-optimization/87763 * simplify-rtx.c (simplify_truncation): Extend sign/zero_extract simplification to handle subregs as well as bare regs. * config/i386/i386.md (*testqi_ext_3): Match QI extracts too.
