mbox

[0/3] Add zero cycle move support

Message ID YZe5llec+qA6YdtE@toto.the-meissners.org
Headers

Message

Michael Meissner Nov. 19, 2021, 2:49 p.m. UTC 
  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.