Src:
https://github.com/golang/go/blob/1d4b0b6236febe0646d8d7b0103da5d169f185cc/src/cmd/compile/internal/reflectdata/reflect.go#L1568-L1594
```
func dgcptrmask(t *types.Type, write bool) *obj.LSym {
...
ptrmask = make([]byte, n)
fillptrmask(t, ptrmask)
...
}
func fillptrmask(t *types.Type, ptrmask []byte) {
for i := range ptrmask {
ptrmask[i] = 0
}
...
}
```
The only caller of fillptrmask is dgcptrmask, so no need to initialize the
ptrmask again.
And from the objdump result of the compiler binary it's not eliminated by
DSE either.
```
➜ linux_amd64 go tool objdump -S ./compile| grep -A 30 "TEXT
cmd/compile/internal/reflectdata.fillptrmask"
TEXT cmd/compile/internal/reflectdata.fillptrmask(SB)
cmd/compile/internal/reflectdata/reflect.go
0x719f40 493b6610 CMPQ SP, 0x10(R14)
0x719f44 0f8681010000 JBE 0x71a0cb
0x719f4a 55 PUSHQ BP
0x719f4b 4889e5 MOVQ SP, BP
0x719f4e 4883ec68 SUBQ $0x68, SP
0x719f52 48898c2488000000 MOVQ CX, 0x88(SP)
0x719f5a 48899c2480000000 MOVQ BX, 0x80(SP)
0x719f62 4889442460 MOVQ AX, 0x60(SP)
0x719f67 4885c9 TESTQ CX, CX
0x719f6a 7410 JE 0x719f7c
0x719f6c 4889d8 MOVQ BX, AX
0x719f6f 4889cb MOVQ CX, BX
0x719f72 e8693ad6ff CALL
runtime.memclrNoHeapPointers(SB)
0x719f77 488b442460 MOVQ 0x60(SP), AX
0x719f7c 0f1f4000 NOPL 0(AX)
0x719f80 e81b74ebff CALL
cmd/compile/internal/types.PtrDataSize(SB)
0x719f85 4885c0 TESTQ AX, AX
0x719f88 0f8e99000000 JLE 0x71a027
0x719f8e 488b942488000000 MOVQ 0x88(SP), DX
0x719f96 4889d6 MOVQ DX, SI
0x719f99 c1e203 SHLL $0x3, DX
0x719f9c 8954243c MOVL DX, 0x3c(SP)
0x719fa0 8d7a1f LEAL 0x1f(DX), DI
0x719fa3 c1ff1f SARL $0x1f, DI
0x719fa6 c1ef1b SHRL $0x1b, DI
0x719fa9 8d3cf7 LEAL 0(DI)(SI*8), DI
0x719fac 8d7f1f LEAL 0x1f(DI), DI
0x719faf c1ff05 SARL $0x5, DI
0x719fb2 4863cf MOVSXD DI, CX
0x719fb5 48894c2450 MOVQ CX, 0x50(SP)
```
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