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Cranelift: Tweak cost function to make imul more expensive #12006

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Merged
cfallin merged 2 commits into from
Nov 7, 2025
Merged

Cranelift: Tweak cost function to make imul more expensive #12006

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Cranelift: Tweak cost function to pessimize `select` opcodes
fitzgen Nov 7, 2025
c5f3964
Don't pessimize `select`s that heavily
fitzgen Nov 7, 2025
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15 changes: 12 additions & 3 deletions cranelift/codegen/src/egraph/cost.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -131,18 +131,27 @@ impl Cost {
| Opcode::Ushr
| Opcode::Sshr => Cost::new(3, 0),

// "Expensive" arithmetic.
Opcode::Imul => Cost::new(10, 0),

// Everything else.
_ => {
// By default, be slightly more expensive than "simple"
// arithmetic.
let mut c = Cost::new(4, 0);

// And then get more expensive as the opcode does more side
// effects.
if op.can_trap() || op.other_side_effects() {
c = c + Cost::new(5, 0);
c = c + Cost::new(10, 0);
}
if op.can_load() {
c = c + Cost::new(10, 0);
c = c + Cost::new(20, 0);
}
if op.can_store() {
c = c + Cost::new(20, 0);
c = c + Cost::new(50, 0);
}

c
}
}
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