Jeff Law via Gcc-patches <gcc-patches@gcc.gnu.org> writes: > On 11/13/20 1:24 AM, Richard Sandiford via Gcc-patches wrote: >> This patch rewrites fwprop.c to use the RTL SSA framework. It tries >> as far as possible to mimic the old behaviour, even in caes where >> that doesn't fit naturally with the new framework. I've added ??? >> comments to mark those places, but I think “fixing” them should >> be done separately to make bisection easier. >> >> In particular: >> >> * The old implementation iterated over uses, and after a successful >> substitution, the new insn's uses were added to the end of the list. >> The pass still processed those uses, but because it processed them at >> the end, it didn't fully optimise one instruction before propagating >> it into the next. >> >> The new version follows the same approach for comparison purposes, >> but I'd like to drop that as a follow-on patch. >> >> * The old implementation operated on single use sites (DF_REF_LOCs). >> This doesn't work well for instructions with match_dups, where it's >> necessary to update both an operand and its dups at the same time. >> For example, attempting to substitute into a divmod instruction would >> fail because only the div or the mod side would be updated. >> >> The new version again follows this to some extent for comparison >> purposes (although not exactly). Again I'd like to drop it as a >> follow-on patch. >> >> One difference is that if a register occurs in multiple MEM addresses >> in a set, the new version will try to update them all at once. This is >> what causes the SVE ACLE st4* output to improve. >> >> Also, the old version didn't naturally guarantee termination (PR79405), >> whereas the new one does. >> >> gcc/ >> * fwprop.c: Rewrite to use the RTL SSA framework. >> >> gcc/testsuite/ >> * gcc.dg/rtl/x86_64/test-return-const.c.before-fwprop.c: Don't >> expect insn updates to be deferred. >> * gcc.target/aarch64/sve/acle/asm/st4_s8.c: Expect the addition >> to be folded into the address. >> * gcc.target/aarch64/sve/acle/asm/st4_s8.c: Likewise. > Consider killing the ADD_NOTES bits.
Done (and glad to see it go). > s/eqaul/equal/ to fix a typo. Oops, fixed. > Naturally I'm happy at how much by-hand RTL analysis code just > disappears with this change :-) > > Ideally you'll drop this in tomorrow and we can get a fresh run of all > the targets in my tester before the weekend. I won't be stressed if we > see some fallout, but I don't expect much. I'll help track them down if > they occur. Thanks, now pushed with the above changes. Richard
