cmd/compile/internal/ssa: make oneBit function generic

Allows rewrite rules using oneBit to be made more compact.

Change-Id: I986715f77db5b548759d809fe668e1893048f25c
Reviewed-on: https://go-review.googlesource.com/c/go/+/699295
Reviewed-by: Youlin Feng <[email protected]>
Commit-Queue: Keith Randall <[email protected]>
Auto-Submit: Keith Randall <[email protected]>
Reviewed-by: Keith Randall <[email protected]>
Reviewed-by: Keith Randall <[email protected]>
Reviewed-by: Cherry Mui <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>

Author: Michael Munday

src/cmd/compile/internal/ssa/_gen/generic.rules

@@ -1896,22 +1896,10 @@
 (Neq(8|16|32|64) s:(Sub(8|16|32|64) x y) (Const(8|16|32|64) [0])) && s.Uses == 1 => (Neq(8|16|32|64) x y)
 
 // Optimize bitsets
-(Eq8 (And8 <t> x (Const8 <t> [y])) (Const8 <t> [y])) && oneBit8(y)
-  => (Neq8 (And8 <t> x (Const8 <t> [y])) (Const8 <t> [0]))
-(Eq16 (And16 <t> x (Const16 <t> [y])) (Const16 <t> [y])) && oneBit16(y)
-  => (Neq16 (And16 <t> x (Const16 <t> [y])) (Const16 <t> [0]))
-(Eq32 (And32 <t> x (Const32 <t> [y])) (Const32 <t> [y])) && oneBit32(y)
-  => (Neq32 (And32 <t> x (Const32 <t> [y])) (Const32 <t> [0]))
-(Eq64 (And64 <t> x (Const64 <t> [y])) (Const64 <t> [y])) && oneBit64(y)
-  => (Neq64 (And64 <t> x (Const64 <t> [y])) (Const64 <t> [0]))
-(Neq8 (And8 <t> x (Const8 <t> [y])) (Const8 <t> [y])) && oneBit8(y)
-  => (Eq8 (And8 <t> x (Const8 <t> [y])) (Const8 <t> [0]))
-(Neq16 (And16 <t> x (Const16 <t> [y])) (Const16 <t> [y])) && oneBit16(y)
-  => (Eq16 (And16 <t> x (Const16 <t> [y])) (Const16 <t> [0]))
-(Neq32 (And32 <t> x (Const32 <t> [y])) (Const32 <t> [y])) && oneBit32(y)
-  => (Eq32 (And32 <t> x (Const32 <t> [y])) (Const32 <t> [0]))
-(Neq64 (And64 <t> x (Const64 <t> [y])) (Const64 <t> [y])) && oneBit64(y)
-  => (Eq64 (And64 <t> x (Const64 <t> [y])) (Const64 <t> [0]))
+(Eq(8|16|32|64) (And(8|16|32|64) <t> x (Const(8|16|32|64) <t> [y])) (Const(8|16|32|64) <t> [y])) && oneBit(y)
+  => (Neq(8|16|32|64) (And(8|16|32|64) <t> x (Const(8|16|32|64) <t> [y])) (Const(8|16|32|64) <t> [0]))
+(Neq(8|16|32|64) (And(8|16|32|64) <t> x (Const(8|16|32|64) <t> [y])) (Const(8|16|32|64) <t> [y])) && oneBit(y)
+  => (Eq(8|16|32|64) (And(8|16|32|64) <t> x (Const(8|16|32|64) <t> [y])) (Const(8|16|32|64) <t> [0]))
 
 // Reassociate expressions involving
 // constants such that constants come first,

src/cmd/compile/internal/ssa/rewrite.go

@@ -470,11 +470,10 @@ func ntz32(x int32) int { return bits.TrailingZeros32(uint32(x)) }
 func ntz16(x int16) int { return bits.TrailingZeros16(uint16(x)) }
 func ntz8(x int8) int   { return bits.TrailingZeros8(uint8(x)) }
 
-func oneBit(x int64) bool   { return x&(x-1) == 0 && x != 0 }
-func oneBit8(x int8) bool   { return x&(x-1) == 0 && x != 0 }
-func oneBit16(x int16) bool { return x&(x-1) == 0 && x != 0 }
-func oneBit32(x int32) bool { return x&(x-1) == 0 && x != 0 }
-func oneBit64(x int64) bool { return x&(x-1) == 0 && x != 0 }
+// oneBit reports whether x contains exactly one set bit.
+func oneBit[T int8 | int16 | int32 | int64](x T) bool {
+	return x&(x-1) == 0 && x != 0
+}
 
 // nto returns the number of trailing ones.
 func nto(x int64) int64 {