res.Header = rw.Header()
	res.Body = nil // so res.Write only writes the headers; we have res.Body in backConn above
	if err := res.Write(brw); err != nil {
		p.getErrorHandler()(rw, req, fmt.Errorf("response write: %v", err))
		return
	}
	if err := brw.Flush(); err != nil {
		p.getErrorHandler()(rw, req, fmt.Errorf("response flush: %v", err))
		return
	}
	errc := make(chan error, 1)

// POWER10/ISA 3.1.

#include "../../../../../runtime/textflag.h"

TEXT asmtest(SB), DUPOK|NOSPLIT, $0
	BRD R1, R2                              // 7c220176
	BRH R1, R2                              // 7c2201b6
	BRW R1, R2                              // 7c220136
	CFUGED R1, R2, R3                       // 7c2311b8
	CNTLZDM R2, R3, R1                      // 7c411876
	CNTTZDM R2, R3, R1                      // 7c411c76

	// ppc64x/power10: "BRD"
	return bits.ReverseBytes64(n)
}

func ReverseBytes32(n uint32) uint32 {
	// amd64:"BSWAPL"
	// 386:"BSWAPL"
	// s390x:"MOVWBR"
	// arm64:"REVW"
	// ppc64x/power10: "BRW"
	return bits.ReverseBytes32(n)
}

func ReverseBytes16(n uint16) uint16 {
	// amd64:"ROLW"
	// arm64:"REV16W",-"UBFX",-"ORR"
	// arm/5:"SLL","SRL","ORR"
	// arm/6:"REV16"
	// arm/7:"REV16"

	"MTVSRDM",
	"MTVSRBMI",
	"MTVSRBM",
	"LXVRWX",
	"LXVRHX",
	"LXVRDX",
	"LXVRBX",
	"LXVPX",
	"LXVP",
	"LXVKQ",
	"DCTFIXQQ",
	"DCFFIXQQ",
	"CNTTZDM",
	"CNTLZDM",
	"CFUGED",
	"BRW",
	"BRH",
	"BRD",
	"HASHSTP",
	"HASHST",
	"HASHCHKP",
	"HASHCHK",
	"XXSPLTIW",
	"XXSPLTIDP",
	"XXSPLTI32DX",
	"XXPERMX",
	"XXEVAL",
	"XXBLENDVW",
	"XXBLENDVH",
	"XXBLENDVD",

		{name: "BRD", argLength: 1, reg: gp11, asm: "BRD"},                                              // reversebytes64(arg0)
		{name: "BRW", argLength: 1, reg: gp11, asm: "BRW"},                                              // reversebytes32(arg0)
		{name: "BRH", argLength: 1, reg: gp11, asm: "BRH"},                                              // reversebytes16(arg0)