On 6/5/24 1:47 AM, Fei Gao wrote:
On 2024-06-05 14:36 Kito Cheng <kito.ch...@gmail.com> wrote:
Thanks for fixing this issue, and I am wondering doest it possible to
fix that without introduce target hook? I ask that because...GCC 14
also has this bug, but I am not sure it's OK to introduce new target
hook for release branch? or would you suggest we just revert patch to
fix that on GCC 14?
If hook is unacceptable in GCC14, I suggest to revert on GCC 14 the following
commit.
https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=b27d323a368033f0b37e93c57a57a35fd9997864
I started fixing this issue by adding changes in mach pass but abandoned it
due to the following reasons:
1. more codes to detect location of epilogue in the whole insn list.
2. due to impact by scheduling pass, clear a0 and use a0 insns get reordered,
resulting in more
codes.
3. data flow analysis is needed, but insn does't have bb info any more, so
rescan actually does
nothing, which I guess there's some hidden issue in
riscv_remove_unneeded_save_restore_calls
using dfa.
So I came up this hook based patch in prologue and epilogue pass to make the
optimization
happen as earlier as possible. It ends up with simplicity and clear logic.
But let's back up and get a good explanation of what the problem is.
Based on patch 2/2 it looks like we have lost an assignment to the
return register.
To someone not familiar with this code, it sounds to me like we've made
a mistake earlier and we're now defining a hook that lets us go back and
fix that earlier mistake. I'm probably wrong, but so far that's what
it sounds like.
So let's get a good explanation of the problem and perhaps we'll find a
better way to solve it.
jeff
