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x64: port the remainder of select to ISLE (#3973)

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Previous changes had ported the difficult "`select` based on an `fcmp`"
patterns to ISLE; this completes porting of `select` by moving over the
final two kinds of patterns:
 - `select` based on an `icmp`
 - `select` based on a value
This commit is contained in:
Andrew Brown
2022-03-30 13:32:26 -07:00
committed by GitHub
parent a5752773b2
commit e8dd13cf87
5 changed files with 408 additions and 332 deletions
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37
cranelift/codegen/src/isa/x64/lower.isle
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@@ -1746,6 +1746,43 @@
(rule (lower (has_type ty (select (fcmp (FloatCC.NotEqual) a b) x y)))
(with_flags (x64_ucomis a b) (cmove_or_from_values ty (CC.NZ) (CC.P) x y)))
;; We also can lower `select`s that depend on an `icmp` test, but more simply
;; than the `fcmp` variants above. In these cases, we lower to a `CMP`
;; instruction plus a `CMOV`; recall that `cmove_from_values` here may emit more
;; than one instruction for certain types (e.g., XMM-held, I128).
(rule (lower (has_type ty (select (icmp cc a @ (value_type (fits_in_64 a_ty)) b) x y)))
;; N.B.: we force the comparison operators into registers, and disallow
;; load-op fusion, because we do not have a transitive guarantee that this
;; cmp-site will be the sole user of the value. Consider: the `icmp` might
;; be the only user of a load, but there may be multiple users of the
;; `icmp` (e.g., `select` or `bint` instructions) that each invoke emit a
;; comparison. If we were to allow a load to sink to the *latest* one, but
;; other sites did not permit sinking, then we would be missing the load
;; for other cmp-sites. TODO:
;; https://github.com/bytecodealliance/wasmtime/issues/3953.
(let ((gpr_a Gpr (put_in_gpr a))
(gpr_b Gpr (put_in_gpr b))
(size OperandSize (raw_operand_size_of_type a_ty)))
(with_flags (x64_cmp size gpr_b gpr_a) (cmove_from_values ty cc x y))))
;; Finally, we lower `select` from a condition value `c`. These rules are meant
;; to be the final, default lowerings if no other patterns matched above.
(rule (lower (has_type ty (select c @ (value_type $B1) x y)))
(let ((size OperandSize (raw_operand_size_of_type $B1))
;; N.B.: disallow load-op fusion, see above. TODO:
;; https://github.com/bytecodealliance/wasmtime/issues/3953.
(gpr_c Gpr (put_in_gpr c)))
(with_flags (x64_test size (RegMemImm.Imm 1) gpr_c) (cmove_from_values ty (CC.NZ) x y))))
(rule (lower (has_type ty (select c @ (value_type (fits_in_64 a_ty)) x y)))
(let ((size OperandSize (raw_operand_size_of_type a_ty))
;; N.B.: disallow load-op fusion, see above. TODO:
;; https://github.com/bytecodealliance/wasmtime/issues/3953.
(gpr_c Gpr (put_in_gpr c)))
(with_flags (x64_test size gpr_c gpr_c) (cmove_from_values ty (CC.NZ) x y))))
;; Rules for `clz` ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; If available, we can use a plain lzcnt instruction here. Note no