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Re: define_expand

(define_expand "negsf2"
  [(set (match_operand:SF 0 "gpc_reg_operand" "")
    (neg:SF (match_operand:SF 1 "gpc_reg_operand" "")))]

(define_insn "*negsf2"
  [(set (match_operand:SF 0 "gpc_reg_operand" "=f")
    (neg:SF (match_operand:SF 1 "gpc_reg_operand" "f")))]
  "fneg %0,%1"
  [(set_attr "type" "fp")])

I've read the docs (sect 13.15) which describe define_expand,
but I have a feeling that I'm missing something that would make
it clear how these two templates interact.  Clearly, the define_insn
template says that when the insn pattern is found, generate the
"fneg" instruction.  What is the define_expand template doing?

You are missing another template, which is used on the E500 (see This has a condition of "TARGET_HARD_FLOAT && !TARGET_FPRS".

(define_insn "*negsf2_gpr"
  [(set (match_operand:SF 0 "gpc_reg_operand" "=r")
        (neg:SF (match_operand:SF 1 "gpc_reg_operand" "r")))]
  "efsneg %0,%1"
  [(set_attr "type" "fpsimple")])

We need a define_expand to generate the RTL, and two define_insns to
emit different code depending on the actual subtarget.


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