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.
