https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86891
--- Comment #8 from Richard Earnshaw <rearnsha at gcc dot gnu.org> --- Author: rearnsha Date: Mon Jan 7 14:49:00 2019 New Revision: 267650 URL: https://gcc.gnu.org/viewcvs?rev=267650&root=gcc&view=rev Log: Investigating PR target/86891 revealed a number of issues with the way the AArch64 backend was handing overflow detection patterns. Firstly, expansion for signed and unsigned types is not the same as in one form the overflow is detected via the C flag and in the other it is done via the V flag in the PSR. Secondly, particular care has to be taken when describing overflow of signed types: the comparison has to be performed conceptually on a value that cannot overflow and compared to a value that might have overflowed. It became apparent that some of the patterns were simply unmatchable (they collapse to NEG in the RTL rather than subtracting from zero) and a number of patterns were overly restrictive in terms of the immediate constants that they supported. I've tried to address all of these issues as well. gcc: PR target/86891 * config/aarch64/aarch64.c (aarch64_expand_subvti): New parameter unsigned_p. Handle signed and unsigned overflow correction as required. * config/aarch64/aarch64-protos.h (aarch64_expand_subvti): Update prototype. * config/aarch64/aarch64.md (addv<mode>4): Use aarch64_plus_operand for operand 2. (add<mode>3_compareV_imm): Make this callable for expanding. (subv<GPI:mode>4): Use register_operand for operand 1. Use aarch64_plus_operand for operand 2. (subv<GPI:mode>_insn): New insn pattern. (subv<GPI:mode>_imm): Likewise. (negv<GPI:mode>3): New expand pattern. (negv<GPI:mode>_insn): New insn pattern. (negv<GPI:mode>_cmp_only): Likewise. (cmpv<GPI:mode>_insn): Likewise. (subvti4): Use register_operand for operand 1. Update call to aarch64_expand_subvti. (usubvti4): Likewise. (negvti3): New expand pattern. (negdi_carryout): New insn pattern. (negvdi_carryinV): New insn pattern. (sub<mode3>_compare1_imm): Delete named insn pattern, make anonymous version the named version. (peepholes to convert to sub<mode3>_compare1_imm): Adjust order of operands. (usub<GPI:mode>3_carryinC, usub<GPI:mode>3_carryinC_z1): New insn patterns. (usub<GPI:mode>3_carryinC_z2, usub<GPI:mode>3_carryinC): New insn patterns. (sub<mode>3_carryinCV, sub<mode>3_carryinCV_z1_z2): Delete. (sub<mode>3_carryinCV_z1, sub<mode>3_carryinCV_z2): Delete. (sub<mode>3_carryinCV): Delete. (sub<GPI:mode>3_carryinV): New expand pattern. sub<mode>3_carryinV, sub<mode>3_carryinV_z2): New insn patterns. testsuite: * gcc.target/aarch64/subs_compare_2.c: Make '#' immediate prefix optional in scan pattern. Modified: trunk/gcc/ChangeLog trunk/gcc/config/aarch64/aarch64-protos.h trunk/gcc/config/aarch64/aarch64.c trunk/gcc/config/aarch64/aarch64.md trunk/gcc/testsuite/ChangeLog trunk/gcc/testsuite/gcc.target/aarch64/subs_compare_2.c
