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cmd/compile: ARM64 rule redundancy #20663

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randall77 opened this issue Jun 13, 2017 · 1 comment
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cmd/compile: ARM64 rule redundancy #20663

randall77 opened this issue Jun 13, 2017 · 1 comment
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Go1.10

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@randall77
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(Rsh64x64  x (MOVDconst [c])) && uint64(c) < 64 -> (SRAconst x [c])
(Rsh64x64 x y) -> (SRA x (CSELULT <y.Type> y (Const64 <y.Type> [63]) (CMPconst [64] y)))
(Const64 [val]) -> (MOVDconst [val])
(CMPconst  (MOVDconst [x]) [y]) && int64(x)<int64(y) && uint64(x)<uint64(y) -> (FlagLT_ULT)
(CSELULT x _ (FlagGT_ULT)) -> x
(SRA x (MOVDconst [c])) -> (SRAconst x [c&63])

The first rule is implied by the other rules. We don't need the first rule (except that it reduces the number of rewrites required).
We should also probably use MOVDconst instead of Const64 in rule #2.
@randall77 randall77 added this to the Go1.10 milestone Jun 13, 2017
@cherrymui cherrymui self-assigned this Jun 14, 2017
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Change https://golang.org/cl/60330 mentions this issue: cmd/compile: remove redundant constant shift rules

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