https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81803
--- Comment #9 from mpf at gcc dot gnu.org --- Created attachment 42075 --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=42075&action=edit Proposed fix Off-thread James pointed out that one of my patches I did last year appeared to fix this issue but it was one I reverted owing to breaking ARM (and probably others). The thread was: https://gcc.gnu.org/ml/gcc-patches/2017-02/msg00518.html At the time I thought I had fixed the same problem twice and that the changes to simplify_operand_subreg were sufficient. It occurs to me however that simplify_operand_subreg only has the opportunity to fix WORD_REGISTER_OPERATIONS issues affecting subreg(mem) patterns not subreg(reg) patterns where reg is a pseudo that may yet be spilled. I can't say that I am 100% convinced yet with my thinking here but I've attached an updated version of the original patch with some changes: * Incorporated Eric's feedback on the original patch to check GET_MODE_PRECISION instead of GET_MODE_SIZE for comparing whether a mode is strictly narrower * Limited the test to word sized inner modes or smaller * Limited the test to OP_OUT or OP_INOUT as I can't see any reason why it would matter if we do a narrower input reload This is barely tested but does fix testcase-c which is the only one I can get to trigger.
