missed optimizatino

asm-via-ll.s

	.file	"asm.ll"
	.text
	.globl	_Z4testR6Server
	.align	16, 0x90
	.type	_Z4testR6Server,@function
_Z4testR6Server:                        # @_Z4testR6Server
	.cfi_startproc
# BB#0:
	pushq	%rax
.Ltmp1:
	.cfi_def_cfa_offset 16
	xorl	%esi, %esi
	movl	$8192, %edx             # imm = 0x2000
	callq	memset
	popq	%rax
	ret
.Ltmp2:
	.size	_Z4testR6Server, .Ltmp2-_Z4testR6Server
	.cfi_endproc


	.section	".note.GNU-stack","",@progbits

asm.cpp

#include <cstring>

#define MAX_MAP_PER_SERVER 512

struct Server
{
    char maps[MAX_MAP_PER_SERVER][16];
};

inline
void strzcpy(char *dest, const char *src, size_t n)
{
    if (n)
    {
        strncpy(dest, src, n);
        dest[n - 1] = '\0';
    }
}

void test(Server& srv)
{
    for (char (&it)[16] : srv.maps)
        strzcpy(it, "", 16);
}

asm.ll

; ModuleID = 'asm.cpp'
target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64-S128"
target triple = "x86_64-pc-linux-gnu"

%struct.Server = type { [512 x [16 x i8]] }

; Function Attrs: nounwind uwtable
define void @_Z4testR6Server(%struct.Server* %srv) #0 {
  %1 = getelementptr inbounds %struct.Server* %srv, i64 0, i32 0, i64 0
  %2 = getelementptr inbounds %struct.Server* %srv, i64 0, i32 0, i64 512
  br label %3

; <label>:3                                       ; preds = %0, %3
  %__begin.01 = phi [16 x i8]* [ %1, %0 ], [ %4, %3 ]
  %4 = getelementptr inbounds [16 x i8]* %__begin.01, i64 1
  %5 = icmp eq [16 x i8]* %4, %2
  %6 = getelementptr inbounds [16 x i8]* %__begin.01, i64 0, i64 0
  call void @llvm.memset.p0i8.i64(i8* %6, i8 0, i64 16, i32 1, i1 false)
  br i1 %5, label %7, label %3

; <label>:7                                       ; preds = %3
  ret void
}

; Function Attrs: nounwind
declare void @llvm.memset.p0i8.i64(i8* nocapture, i8, i64, i32, i1) #1

attributes #0 = { nounwind uwtable "less-precise-fpmad"="false" "no-frame-pointer-elim"="false" "no-frame-pointer-elim-non-leaf"="false" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "unsafe-fp-math"="false" "use-soft-float"="false" }
attributes #1 = { nounwind }

asm.s

	.file	"asm.cpp"
	.text
	.globl	_Z4testR6Server
	.align	16, 0x90
	.type	_Z4testR6Server,@function
_Z4testR6Server:                        # @_Z4testR6Server
	.cfi_startproc
# BB#0:
	xorl	%eax, %eax
	xorps	%xmm0, %xmm0
	.align	16, 0x90
.LBB0_1:                                # =>This Inner Loop Header: Depth=1
	movups	%xmm0, (%rdi,%rax)
	addq	$16, %rax
	cmpq	$8192, %rax             # imm = 0x2000
	jne	.LBB0_1
# BB#2:
	ret
.Ltmp0:
	.size	_Z4testR6Server, .Ltmp0-_Z4testR6Server
	.cfi_endproc


	.section	".note.GNU-stack","",@progbits