Hello Segher, all,
- On the issue of the restore of R18 in mode DI, it seems from
analysing the log file that the compiler does not understand this
also affects R19. This looks a bug to me ??. Anyway, I have resolved
this, by adding a 'clobber' statement to R19 when R18 is written
in mode 'DI'.
- The other issue, I have changed ((set) (pc) (return)) to (return),
but, as far as I understand the logfiles, and the documentation,
both forms are equivalent. Anyway, after fixing the first issue, I do
not see the second issue any more.
Best Regards and thanks,
Henri.
On 02/26/2020 01:59 PM, Segher Boessenkool wrote:
Hi!
On Wed, Feb 26, 2020 at 01:02:46PM +0100, Henri Cloetens wrote:
1. The epilogue generator emits an instruction "popret_internal" that
a. Restores R18 in mode DI. (which corresponds to R18 and R19 in
mode SI)
b. Does the function return.
2. Then, during scheduling, the compiler shifts an add instruction PAST
this return
instruction, which is incorrect, because:
(a.) The instruction writes R19. (it restores R18 and R19). The
scheduler should see this.
Yes. So why doesn't it? Look at the various dump files to see what the
df ("dataflow") framework thinks about this.
(b.) The instruction changes the PC (program counter).
The documentation says you should write just
(return)
instead of
(set (pc) (return))
(unlikely to be causing any of this, but a good cleanup to make).
Q. Why is this happening ?. How can I prevent this ?.
You can have the scheduler print much more debugging info, but I'd
start with the usual stuff: -dap.
Segher
