cmd/compile: use unsigned power-of-two detector for unsigned mod

Same as CL 689815, but for modulus instead of division.

Updates #74485

Change-Id: I73000231c886a987a1093669ff207fd9117a8160
Reviewed-on: https://go-review.googlesource.com/c/go/+/689895
LUCI-TryBot-Result: Go LUCI <[email protected]>
Reviewed-by: David Chase <[email protected]>
Auto-Submit: Cuong Manh Le <[email protected]>
Reviewed-by: Keith Randall <[email protected]>
Reviewed-by: Keith Randall <[email protected]>

Author: cuonglm

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

@@ -1293,11 +1293,10 @@
       (Const64 <typ.UInt64> [63])))
 
 // Unsigned mod by power of 2 constant.
-(Mod8u  <t> n (Const8  [c])) && isPowerOfTwo(c) => (And8  n (Const8  <t> [c-1]))
-(Mod16u <t> n (Const16 [c])) && isPowerOfTwo(c) => (And16 n (Const16 <t> [c-1]))
-(Mod32u <t> n (Const32 [c])) && isPowerOfTwo(c) => (And32 n (Const32 <t> [c-1]))
-(Mod64u <t> n (Const64 [c])) && isPowerOfTwo(c) => (And64 n (Const64 <t> [c-1]))
-(Mod64u <t> n (Const64 [-1<<63]))                 => (And64 n (Const64 <t> [1<<63-1]))
+(Mod8u  <t> n (Const8  [c])) && isUnsignedPowerOfTwo(uint8(c)) => (And8  n (Const8  <t> [c-1]))
+(Mod16u <t> n (Const16 [c])) && isUnsignedPowerOfTwo(uint16(c)) => (And16 n (Const16 <t> [c-1]))
+(Mod32u <t> n (Const32 [c])) && isUnsignedPowerOfTwo(uint32(c)) => (And32 n (Const32 <t> [c-1]))
+(Mod64u <t> n (Const64 [c])) && isUnsignedPowerOfTwo(uint64(c)) => (And64 n (Const64 <t> [c-1]))
 
 // Signed non-negative mod by power of 2 constant.
 (Mod8  <t> n (Const8  [c])) && isNonNegative(n) && isPowerOfTwo(c) => (And8  n (Const8  <t> [c-1]))

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

@@ -25,3 +25,23 @@ func divUint8(b uint8) uint8 {
 	// amd64:"SHRB	[$]7, AL"
 	return b / 128
 }
+
+func modUint64(b uint64) uint64 {
+	// amd64:"BTRQ	[$]63, AX"
+	return b % 9223372036854775808
+}
+
+func modUint32(b uint32) uint32 {
+	// amd64:"ANDL	[$]2147483647, AX"
+	return b % 2147483648
+}
+
+func modUint16(b uint16) uint16 {
+	// amd64:"ANDL	[$]32767, AX"
+	return b % 32768
+}
+
+func modUint8(b uint8) uint8 {
+	// amd64:"ANDL	[$]127, AX"
+	return b % 128
+}