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cranelift/egraphs: more select/bitselect optimizations #6214

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cranelift/egraphs: more select/bitselect optimizations #6214

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18 changes: 18 additions & 0 deletions cranelift/codegen/src/opts/selects.isle
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Original file line number Diff line number Diff line change
Expand Up @@ -4,6 +4,24 @@
(rule (simplify (select ty _ x x)) x)
(rule (simplify (bitselect ty _ x x)) x)

;; bmask of a truthy scalar integer creates a mask that causes bitselect to
;; select values fully from one input or the other, same as select.
(rule (simplify (bitselect ty (bmask ty c) x y)) (select ty c x y))

;; bmask and negation both preserve truthiness, so they can be removed from any
;; instruction that only considers truthiness.
(rule (simplify (bmask ty (bmask ty c))) (bmask ty c))
(rule (simplify (bmask ty (ineg ty c))) (bmask ty c))
(rule (simplify (select ty (bmask ty c) x y)) (select ty c x y))
(rule (simplify (select ty (ineg ty c) x y)) (select ty c x y))
(rule (simplify (select_spectre_guard ty (bmask ty c) x y)) (select_spectre_guard ty c x y))
(rule (simplify (select_spectre_guard ty (ineg ty c) x y)) (select_spectre_guard ty c x y))

;; bitwise-not of bmask inverts truthiness, swapping branches
(rule (simplify (select ty (bnot ty (bmask ty c)) x y)) (select ty c y x))
(rule (simplify (select_spectre_guard ty (bnot ty (bmask ty c)) x y)) (select_spectre_guard ty c y x))
(rule (simplify (bitselect ty (bnot ty c) x y)) (bitselect ty c y x))

;; Transform select-of-icmp into {u,s}{min,max} instructions where possible.
(rule (simplify (select ty (sgt _ x y) x y)) (smax ty x y))
(rule (simplify (select ty (sge _ x y) x y)) (smax ty x y))
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