https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115687
--- Comment #4 from palmer at gcc dot gnu.org --- Just poking around a bit: I think this is coming from CSE, which is replacing (insn 5 2 6 2 (set (reg:DI 135) (const_int 16384 [0x4000])) "pr115687.c":7:12 275 {*movdi_64bit} (nil)) (insn 6 5 7 2 (set (reg:DI 12 a2) (plus:DI (reg:DI 135) (const_int -16 [0xfffffffffffffff0]))) "pr115687.c":7:12 5 {adddi3} (expr_list:REG_EQUAL (const_int 16368 [0x3ff0]) (nil))) (insn 7 6 8 2 (set (reg:DI 136) (const_int 16384 [0x4000])) "pr115687.c":7:12 275 {*movdi_64bit} (nil)) (insn 8 7 9 2 (set (reg:DI 11 a1) (plus:DI (reg:DI 136) (const_int 32 [0x20]))) "pr115687.c":7:12 5 {adddi3} (expr_list:REG_EQUAL (const_int 16416 [0x4020]) (nil))) (insn 9 8 10 2 (set (reg:DI 137) (const_int 16384 [0x4000])) "pr115687.c":7:12 275 {*movdi_64bit} (nil)) with (insn 5 2 6 2 (set (reg:DI 135) (const_int 16384 [0x4000])) "pr115687.c":7:12 275 {*movdi_64bit} (nil)) (insn 6 5 7 2 (set (reg:DI 12 a2) (const_int 16368 [0x3ff0])) "pr115687.c":7:12 273 {*mvconst_internal} (expr_list:REG_DEAD (reg:DI 135) (expr_list:REG_EQUAL (const_int 16368 [0x3ff0]) (nil)))) (insn 7 6 8 2 (set (reg:DI 136) (reg:DI 135)) "pr115687.c":7:12 275 {*movdi_64bit} (expr_list:REG_EQUAL (const_int 16384 [0x4000]) (nil))) (insn 8 7 9 2 (set (reg:DI 11 a1) (const_int 16416 [0x4020])) "pr115687.c":7:12 273 {*mvconst_internal} (expr_list:REG_DEAD (reg:DI 136) (expr_list:REG_EQUAL (const_int 16416 [0x4020]) (nil)))) (insn 9 8 10 2 (set (reg:DI 137) (reg:DI 135)) "pr115687.c":7:12 275 {*movdi_64bit} (expr_list:REG_EQUAL (const_int 16384 [0x4000]) (nil))) (insn 10 9 11 2 (set (reg:DI 10 a0) (const_int 16400 [0x4010])) "pr115687.c":7:12 273 {*mvconst_internal} (expr_list:REG_DEAD (reg:DI 137) (expr_list:REG_EQUAL (const_int 16400 [0x4010]) (nil)))) that seems to be as-designed -- or at least as this comment in cse.cc seems to be describing /* Find cheapest and skip it for the next time. For items of equal cost, use this order: src_folded, src, src_eqv, src_related and hash table entry. */ That seems like a bit of a heuristic, but I haven't poked around this stuff to really understand how it's handling multiple uses of the incoming constant anchor.