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)
