Hi Jiong,
Jiong Wang wrote:
After previous patches, verifier has marked those instructions that really
need zero extension on dst_reg.
Thanks for implementing this -- this is very helpful on architectures
without sub-register instructions, especially in comparison with legacy
BPF, since the move to eBPF resulted in lot more instructions being
generated.
I have a small nit below on the overall approach...
It is then for all back-ends to decide how to use such information to
eliminate unnecessary zero extension code-gen during JIT compilation.
One approach is:
1. Verifier insert explicit zero extension for those instructions that
need zero extension.
2. All JIT back-ends do NOT generate zero extension for sub-register
write any more.
Is it possible to instead give a hint to the JIT back-ends on the
instructions needing zero-extension? That would help in case of
architectures that have single/more-optimal instruction for zero
extension, compared to having to emit 2 instructions with the current
approach.
- Naveen
