Bill and David, Currently, the absolute jump table is not by default enabled. It can be enabled by undocumented option "-mno-relative-jumptables". If the target supports named sections (have_named_sections), the feature can be enabled. We plan to enable the future by default in GCC12 and there is a ticket for it. Latest status is that I am waiting for comments on my patch. (https://github.ibm.com/wschmidt/power-gcc/issues/998#issuecomment-34643825). Thanks.
|| On 23/11/2021 上午 12:09, David Edelsohn wrote: > On Mon, Nov 22, 2021 at 10:58 AM Bill Schmidt <wschm...@linux.ibm.com> wrote: >> Hi! >> >> On 11/19/21 8:49 AM, Michael Meissner wrote: >>> The next set of 3 patches add zero cycle move support to the Power10. Zero >>> cycle moves are where the move to LR/CTR/TAR register that is adjacent to >>> the >>> jump to LR/CTR/TAR register can be fused together. >>> >>> At the moment, these set of three patches add support for zero cycle moves >>> for >>> indirect jumps and switch tables using the CTR register. Potential zero >>> cycle >>> moves for doing returns are not currently handled. >>> >>> In looking at the code, I discovered that just using zero cycle moves isn't >>> as >>> helpful unless we can eliminate the add instruction before doing the jump. >>> I >>> also noticed that the various power10 fusion options are only done if >>> -mcpu=power10. I added a patch to do the fusion for -mtune=power10 as well. >>> >>> I have done bootstraps and make check with these patches installed on both >>> little endian power9 and little endian power10 systems. Can I install these >>> patches? >>> >>> The following patches will be posted: >>> >>> 1) Patch to add zero cycle move for indirect jumps and switches. >>> >>> 2) Patch to enable p10 fusion for -mtune=power10 in addition to >>> -mcpu=power10. >>> >>> 3) Patch to use absolute addresses for switch tables instead of relative >>> addresses if zero cycle fusion is enabled. >>> >> For this last point, I had thought that the plan was to always switch over to >> absolute addresses for switch tables, following the work that Hao Chen did in >> this area. Am I misremembering? Hao Chen, can you please remind me where we >> ended up here? > And do the absolute addressing for switch tables changes work on AIX? > I thought that Hao Chen only had done the work for PPC64 Linux ELF > syntax with promises of future changes to accommodate AIX as well. > > Thanks, David
