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Cranelift: Add egraph rule to rewrite x * C ==> x << log2(C) when C is a power of two (#5647)

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Nick Fitzgerald
2023-01-31 10:04:17 -08:00
committed by GitHub
parent 61270cdaed
commit c9d1c068bc
6 changed files with 64 additions and 4 deletions
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8
cranelift/codegen/src/opts/algebraic.isle
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@@ -144,6 +144,12 @@
(rule (simplify (imul ty (iconst _ (simm32 2)) x))
(iadd ty x x))
;; x*c == x<<log2(c) when c is a power of two.
(rule (simplify (imul ty x (iconst _ (imm64_power_of_two c))))
(ishl ty x (iconst ty (imm64 c))))
(rule (simplify (imul ty (iconst _ (imm64_power_of_two c)) x))
(ishl ty x (iconst ty (imm64 c))))
;; x<<32>>32: uextend/sextend 32->64.
(rule (simplify (ushr $I64 (ishl $I64 (uextend $I64 x @ (value_type $I32)) (iconst _ (simm32 32))) (iconst _ (simm32 32))))
(uextend $I64 x))
@@ -151,7 +157,7 @@
(rule (simplify (sshr $I64 (ishl $I64 (uextend $I64 x @ (value_type $I32)) (iconst _ (simm32 32))) (iconst _ (simm32 32))))
(sextend $I64 x))
;; TODO: strength reduction: mul/div to shifts
;; TODO: strength reduction: div to shifts
;; TODO: div/rem by constants -> magic multiplications
;; Rematerialize ALU-op-with-imm and iconsts in each block where they're