I am debugging an old backend for a custom machine (sorry this is a question regarding a very old compiler, but I checked new sources and they look similar). The problem is the following. The backend does support passing struct function argument via registers. For a given function, I see that this is happening, but when accessing member of the struct, the entire struct is first copied to the stack before being accessed. This is happening in assign_parms, because the argument is BLKmode: See "If a BLKmode arrives in registers, copy it to a stack slot" comment in function.c:asign_parms. What causes it to be BLKmode? I debugged a x86 equivalent of the same version, and I see the same C-code leading to the struct being passed in DImode to assign_parms. Hence, I guess something in my backend must cause this. Any hints where I should look? I am seeing that if the parameters are going in DImode to assign_parms, this is much better for the code generated later, in some cases unnecessary copies to the stack are avoided. Thanks, Regards, Hendrik Greving
