"Bingfeng Mei" <[EMAIL PROTECTED]> writes: > We are portinng GCC 4.2.1 to a 2-issue VLIW processor. There are some > special instructions which can only be issued on the second slot (slot > 1). I tried to specify using following DFA constructs. > > ;; Define this instruction can only be issued on slot 1 > (define_insn_reservation "psr_y" 1 > (eq_attr "type" "psr") > "slot1" ) > > ;; Define slot1 can only be issued after slot0 is filled > (presence_set "slot1" "slot0") > > > I hope the compiler can automatically insert NOP on slot0 if it is > unused so that the second constraint can be fulfilled. However, the > compiler falls into a deadlock. Without the second constraint , the > compiler can emit code but I cannot tell from RTL on which slot the > instruction is issued. What is best way to figure out unused slot and > insert NOP insn? Or is there more clever way to specify DFA that allows > compiler automatically emit NOPs? Any suggestion is greatly > appreciated.
You can't do this in gcc's scheduler DFA. It's one of its major limitations. There are a couple of ways to handle this. My personal favorite is to do it in the TARGET_ASM_FUNCTION_PROLOGUE routine. For an example of this approach see frv_pack_insns in frv.c. Ian
