------- Additional Comments From joern dot rennecke at st dot com 2005-04-11 12:36 ------- Subject: Re: TRULY_NOOP_TRUNCATION ignored
echristo at redhat dot com wrote: >------- Additional Comments From echristo at redhat dot com 2005-04-10 19:02 >------- >I think I'm ok with this, but I'd like a bit more info. What changes to the >backend do you forsee this needing? The one patch that you applied to the 4.1 >sh >branch was too big to just get that particular set of changes. > > > [assuming you are talking about generating TRUNCATE in gen_lowpart_common] First. some source operands will have a TRUNCATE, and if your expander tries to make all operands fit, or thinks it knows all the codes that can occur in some position, it will have to be updated to cope with the TRUNCATE. This is unfortunately also true for destination operands. Also, when you use gen_lowpart for a non-TRULY_NOOP_TRUNCATION mode pair, in a splitter or a peephole, for a destination, or for an operand where due to the nature of the operation or the register class being used a SUBREG is desired, you will still get a TRUNCATE; you have to use simplyfy_gen_subreg to explicitly get a SUBREG. The splitter with the for_each_rtx application of shmedia_cleanup_truncate cleans up such stuff after reload. -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=20396
