70 lines
2.8 KiB
Rust
70 lines
2.8 KiB
Rust
//! Instruction shrinking.
|
|
//!
|
|
//! Sometimes there are multiple valid encodings for a given instruction. Cranelift often initially
|
|
//! chooses the largest one, because this typically provides the register allocator the most
|
|
//! flexibility. However, once register allocation is done, this is no longer important, and we
|
|
//! can switch to smaller encodings when possible.
|
|
|
|
use ir::instructions::InstructionData;
|
|
use ir::Function;
|
|
use isa::TargetIsa;
|
|
use regalloc::RegDiversions;
|
|
use timing;
|
|
|
|
/// Pick the smallest valid encodings for instructions.
|
|
pub fn shrink_instructions(func: &mut Function, isa: &TargetIsa) {
|
|
let _tt = timing::shrink_instructions();
|
|
|
|
let encinfo = isa.encoding_info();
|
|
let mut divert = RegDiversions::new();
|
|
|
|
for ebb in func.layout.ebbs() {
|
|
divert.clear();
|
|
for inst in func.layout.ebb_insts(ebb) {
|
|
let enc = func.encodings[inst];
|
|
if enc.is_legal() {
|
|
// regmove/regfill/regspill are special instructions with register immediates
|
|
// that represented as normal operands, so the normal predicates below don't
|
|
// handle them correctly.
|
|
//
|
|
// Also, they need to be presented to the `RegDiversions` to update the
|
|
// location tracking.
|
|
//
|
|
// TODO: Eventually, we want the register allocator to avoid leaving these special
|
|
// instructions behind, but for now, just temporarily avoid trying to shrink them.
|
|
match func.dfg[inst] {
|
|
InstructionData::RegMove { .. }
|
|
| InstructionData::RegFill { .. }
|
|
| InstructionData::RegSpill { .. } => {
|
|
divert.apply(&func.dfg[inst]);
|
|
continue;
|
|
}
|
|
_ => (),
|
|
}
|
|
|
|
let ctrl_type = func.dfg.ctrl_typevar(inst);
|
|
|
|
// Pick the last encoding with constraints that are satisfied.
|
|
let best_enc = isa
|
|
.legal_encodings(func, &func.dfg[inst], ctrl_type)
|
|
.filter(|e| encinfo.constraints[e.recipe()].satisfied(inst, &divert, &func))
|
|
.min_by_key(|e| encinfo.bytes(*e))
|
|
.unwrap();
|
|
|
|
if best_enc != enc {
|
|
func.encodings[inst] = best_enc;
|
|
|
|
dbg!(
|
|
"Shrunk [{}] to [{}] in {}, reducing the size from {} to {}",
|
|
encinfo.display(enc),
|
|
encinfo.display(best_enc),
|
|
func.dfg.display_inst(inst, isa),
|
|
encinfo.bytes(enc),
|
|
encinfo.bytes(best_enc)
|
|
);
|
|
}
|
|
}
|
|
}
|
|
}
|
|
}
|