Jakub Jelinek <ja...@redhat.com> writes: > Hi! > > gen_rtx_SUBREG/gen_lowpart_SUBREG ICE when trying to create a subreg > the backend doesn't like, lowpart_subreg returns NULL. But, for debug info > purposes, all lowpart subregs are valid, a subreg in the debug insns or > var-tracking notes is simply a mode punning construct, and even when the > backend doesn't have any instruction to perform such operation, the debugger > can always do the punning. > > var-tracking.c already has code to emit gen_rtx_raw_SUBREG if everything > else fails, the following patch adjusts valtrack.c to do the same thing.
Looks like this has the potential to introduce nested subregs. Also, the problem isn't just that the architecture can't do some accesses easily (such as accessing the high part of a register). It's also that GCC's model of subregs doesn't always give the right answer. E.g. sometimes the endianess of a particular register is the opposite of what GCC expects, or the value is modelled as occupying more than one register but isn't evenly distributed through them. I take your point about this being done in var-tracking.c, but it always seemed dangerous there too... Thanks, Richard
