On Mon, Sep 21, 2020 at 09:13:58AM -0500, Qing Zhao wrote: > > On Sep 18, 2020, at 5:51 PM, Segher Boessenkool > > <seg...@kernel.crashing.org> wrote: > >> B. Will provide a default definition in middle end to generate the > >> zeroing insn for selected registers. Then need to add a new target hook > >> “ZERO_CALL_USED_REGNO_P(REGNO, GPR_ONLY)”, same as A, X86 implementation > >> will be provided in my patch. > > > > Is this just to make the xor thing work? i386 has a peephole to > > transform the mov to a xor for this (and the backend could just handle > > it in its mov<M> patterns, maybe a peephole was easier for i386, no > > idea). > > You mean what’s the purpose of the new target hook > “ZERO_CALL_USED_REGNO_P(REGNO, GPR_ONLY)? > > The purpose of this new target hook is for the target to delete some of the > call_used registers that should not be zeroed, for example, the stack > registers in X86. (St0-st7).
Oh, I didn't see the _P. Maybe give it a better name? Also, a better interface altogether, a call per hard register is a bit much (and easily avoidable). > For other platforms, there might be other call_used registers that should not > be zeroed. But you cannot *add* anything with this interface, and it cannot return different results depending on which return insn this is. It is not a good abstraction IMO. Segher
