[Bug rtl-optimization/82683] Combine: GCC generates bad code with -tune=thunderx2t99
segher at gcc dot gnu.org
gcc-bugzilla@gcc.gnu.org
Tue Oct 24 12:25:00 GMT 2017
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82683
--- Comment #3 from Segher Boessenkool <segher at gcc dot gnu.org> ---
Ah. So we start with
insn_cost 4 for 18: r91:DI=r83:DI<<0x2
REG_DEAD r83:DI
insn_cost 4 for 19: r78:DI=r76:DI+r91:DI
REG_DEAD r91:DI
REG_DEAD r76:DI
insn_cost 20 for 20: r82:SI=[r78:DI]
REG_DEAD r78:DI
insn_cost 4 for 21: r83:DI=sign_extend(r82:SI)
and first 18,19 are combined, and then 19,20,21. Both 19 and 21 set
r83, it is dead after 19, but that note is put on 21.
More information about the Gcc-bugs
mailing list