On Thu, Jun 06, 2024 at 08:28:57PM +0200, Mikael Pettersson via Gcc wrote: > I'm working on a GCC backend for an older processor with very > primitive addressing support. The only way to load from or store to > memory is to compute the address into a register, and then use that > register in the load or store instruction. There are no immediate or > register offsets in memory accesses. > > So what I need is for GCC to transform any > > y = *(r + x); > > into > > t = r + x; > y = *t; > > and similarly for stores. The problem is that however I try to model > that (rewrites in define_expands, patterns in the define_insns, or > extra predicates and constraint letters) GCC goes into reload loops. I > suspect that reloading assumes it can use SP+offset addressing modes > without needing new temps. > > My current workaround is to reserve a register as a hidden spill temp, > and invoke code from the insn patterns to change the output templates > to the equivalent of the above when needed, but it's not a good > solution. > > Are there any targets in current GCC with similar constraints? > > Do you have any other recommendations on how to deal with these > constraints in GCC? > > Thanks in advance, > > /Mikael > > (p.s. please CC me on any replies as I'm not subscribed to this mailing list)
Hi Mikael, Have you tried defining TARGET_LEGITIMIZE_ADDRESS for your target? From a quick search I see that the iq2000 and rx backends are rewriting some PLUS expression addresses with insn sequence to calculate the address. Regards, Dimitar
