On Tue, Aug 15, 2006 at 10:52:01AM -0700, Michael Eager wrote: > (define_expand "negsf2" > [(set (match_operand:SF 0 "gpc_reg_operand" "") > (neg:SF (match_operand:SF 1 "gpc_reg_operand" "")))] > "TARGET_HARD_FLOAT" > "")
> 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? The important thing about the define_expand pattern, in this case, is that it has a name. A call to gen_negsf2 will generate the RTL specified by that expander. This also gets automatically handled by optabs.c when generating negation, and there may be macros like HAVE_negsf2. Then, the *negsf2 define_insn is used to actually emit the operation (and for things like combine, which test if an instruction is valid). -- Daniel Jacobowitz CodeSourcery
