https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63281
--- Comment #14 from Jiu Fu Guo <guojiufu at gcc dot gnu.org> ---
For constant like 0x000800004100001, which is using 5 insns, at 'expand' pass,
it is treated as preferred to save in memory, while at cse1 pass, it was
replaced back to constant.
expand:
7: r119:DI=[unspec[`*.LC0',%r2:DI] 47]
REG_EQUAL 0x800004100001
8: [r117:DI]=r119:DI
cse1:
7: r119:DI=0x800004100001
REG_EQUAL 0x800004100001
8: [r117:DI]=r119:DI
This is because:
expand_assignment invoke force_const_mem/gen_const_mem under the condition:
(num_insns_constant (operands[1], mode) > (TARGET_CMODEL != CMODEL_SMALL ? 3 :
2))
At cse1, when comparing the cost between 'fold_const' and 'src', 'fold_const'
is selected
'preferable (src_folded_cost, src_folded_regcost, src_cost, src_regcost) <= 0'
src:
(mem/u/c:DI (unspec:DI [
(symbol_ref/u:DI ("*.LC0") [flags 0x82])
(reg:DI 2 2)
] UNSPEC_TOCREL) [2 S8 A8])
fold_const:
(const_int 140737556512769 [0x800004100001])
It would be a way to keep the data in memory(.rodata) through adjusting the
cost of constant.
