Sorry for the slow reply. Christophe Lyon <christophe.l...@st.com> writes: > On 16/07/2019 13:58, Richard Sandiford wrote: >> Christophe Lyon <christophe.l...@st.com> writes: >>> +(define_insn "*restore_pic_register_after_call" >>> + [(parallel [(unspec [(match_operand:SI 0 "s_register_operand" "=r,r") >>> + (match_operand:SI 1 "nonimmediate_operand" "r,m")] >>> + UNSPEC_PIC_RESTORE) >>> + (use (match_dup 1)) >>> + (clobber (match_dup 0))]) >>> + ] >>> + "" >>> + "@ >>> + mov\t%0, %1 >>> + ldr\t%0, %1" >>> +) >>> + >>> (define_expand "call_internal" >>> [(parallel [(call (match_operand 0 "memory_operand" "") >>> (match_operand 1 "general_operand" "")) >> >> Since operand 0 is significant after the instruction, I think this >> should be: >> >> (define_insn "*restore_pic_register_after_call" >> [(set (match_operand:SI 0 "s_register_operand" "+r,r") >> (unspec:SI [(match_dup 0) >> (match_operand:SI 1 "nonimmediate_operand" "r,m")] >> UNSPEC_PIC_RESTORE))] >> ... >> >> The (use (match_dup 1)) looks redundant, since the unspec itself >> uses operand 1. >> > When I try that, I have cases where the restore instruction is discarded, > when the call happens just before function return. Since r9 is caller-saved, > it should be restored but after dse2 the dumps say: > (insn (set (reg:SI 9 r9) > (unspec:SI [ > (reg:SI 9 r9) > (reg:SI 4 r4 [121]) > ] UNSPEC_PIC_RESTORE)) > (expr_list:REG_UNUSED (reg:SI 9 r9) (nil)))) > > and this is later removed by cprop_hardreg (which says the exit block uses > r4, sp, and lr: should I make it use r9?)
But if it's caller-saved (i.e. call-clobbered), function A shouldn't need to restore r9 after a call unless A needs the value of r9 for something. I.e. A shouldn't need to restore r9 for A's own caller, because the caller should be doing that iself. So if r9 is caller-saved and not referenced between the call and function exit, deleting the restore sounds like the right thing to do. Richard
