Cranelift: Improve codegen of store_imm on x64 #6979
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Adds a new x64 rule for directly lowering stores of immediates with a MOV instruction.
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Thanks for this!
There's a few tests which need to be updated which can be done with CRANELIFT_TEST_BLESS=1 cargo run test filetests from the cranelift directory. Otherwise though could you additionally add some *.clif tests in the cranelift/filetests/filetests/isa/x64/ directory specifically for these lowering rules? I think it'd be good to showcase a range of constants being stored to ensure that they call get codegen'd correctly.
| ;; IMM stores | ||
| (rule 2 (lower (store flags (has_type (fits_in_64 ty) (iconst (u64_from_imm64 value))) address offset)) | ||
| (side_effect | ||
| (x64_movimm_m ty (to_amode flags address offset) value))) |
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If you're up for it I think it might be good to update the MovImmM variant itself. Looking at emit.rs it will panic if the low 32-bits of the value here don't sign-extend into the full 64-bits, so the MovImmM should I think store i32 instead of i64. With that you could add extra matching here that value fits within a 32-bit signed integer.
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Thanks for the review. I've updated the Changing |
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| I::I64(v) => match v.try_into() { | ||
| Ok(v) => self.asm.mov_im(v, &dst, size), | ||
| Err(_) => { | ||
| panic!("Immediate-to-memory moves require immediate operand to sign-extend to 64 bits."); | ||
| } | ||
| }, |
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cc @saulecabrera, this is making the preexisting panic more explicit but it's one where I think the Err case will want to be handled via a move-to-register then store instruction.
(in a future PR, no need to do anything here @mchesser)
* Improve lowering of store_imm on x64 Adds a new x64 rule for directly lowering stores of immediates with a MOV instruction. * Ensure that the MovImmM operand fits in an i32 and add tests. * Update winch to handle MovImmM change
* Improve lowering of store_imm on x64 Adds a new x64 rule for directly lowering stores of immediates with a MOV instruction. * Ensure that the MovImmM operand fits in an i32 and add tests. * Update winch to handle MovImmM change
Improve code generation of store_imm on x64 by adding a new rule that directly handles stores of small immediates.
Currently storing to constant to memory is achieved by first copying the constant into a temporary register, then performing a store of the register value to memory. For example:
Is currently compiled to:
On x86 constants can be stored directly to memory, e.g., after this patch, the constant is inlined into the store instruction removing the extra temporary register.
The overall performance impact is probably very minimal, but it could help with frontend/decoder pressure in cases where this pattern is common.
(Draft PR since this was partially an exercise in understanding ISLE so I could be missing something here).