rs6000: Update sign extension computation with sext_hwi
This patch just replaces the expression like:
((value & 0xf..f) ^ 0x80..0) - 0x80..0 to better code(e.g. sext_hwi) for
rs6000.cc, rs6000.md and predicates.md (files under rs6000/).
gcc/ChangeLog:
* config/rs6000/predicates.md: Use sext_hwi.
* config/rs6000/rs6000.cc (num_insns_constant_gpr): Likewise.
(darwin_rs6000_legitimate_lo_sum_const_p): Likewise.
(mem_operand_gpr): Likewise.
(mem_operand_ds_form): Likewise.
(rs6000_legitimize_address): Likewise.
(rs6000_emit_set_const): Likewise.
(rs6000_emit_set_long_const): Likewise.
(print_operand): Likewise.
(constant_generates_xxspltiw): Remove unnecessary expressions.
* config/rs6000/rs6000.md: Use sext_hwi.