Stream: git-cranelift

Topic: cranelift / Issue #971 Extend constant pools to support f...

GitHub (Feb 28 2020 at 23:26):

alexcrichton transferred Issue #971:

As of today, there's a concept of constant pools in Cranelift, that works for SIMD 128-bits values. I'd like to extend it to work also for float32 and float64 values, to avoid the need for the bitcast, which I'm sure is pretty terrible performance-wise (and doesn't help register allocation either, since it requires one GPR register with a very short lifetime).

My current plan is the following:

• the uimm128 immediate could be reused to store any kind of constants, since it contains an ir::Constant (handle to a vector of bytes of any size); it would be renamed to constant.
• a new instruction load_from_constant_pool would be introduced, taking an input constant value.
• vconst right now can be inserted in the constant pool only from the parser. It'd be nice if this were done during codegen itself. We could recycle "expand_fconst" to do this and legalize vconst / f32const / f64const into a load_from_constant_pool with the right Constant.
• we switch the encodings of vconst to work for load_from_constant_pool on the same types; and we add encodings for f32/f64.

Aligning the constant pool values would be nice to have but not required at this point; it would just be a performance fault on x86.

@abrown Does it sound reasonable to you?

Last updated: Dec 23 2024 at 13:07 UTC