当使用不安全语句和分支的组合时，可能会发出不正确的IL

这里有一个非常简单的C#控制台应用程序/框架4.5，使用Visual Studio 2013 Update 2编译。它从字节数组中读取一个double，并事先进行简单的范围检查。

class Program
{
    private static byte[] fData = new byte[8];
    public static unsafe double ReadDouble(int offset)
    {
        if ((offset + 8) > fData.Length)
            return 0;
        double value = 0;
        fixed (byte* pBuffer = fData)
            value = *((double*)(pBuffer));
        Console.WriteLine("This code is never reached!");
        return value;
    }
    static void Main(string[] args)
    {
        fData = BitConverter.GetBytes(1234.56789d);
        double result = ReadDouble(0);
        Console.WriteLine("result: {0}", result);
        Console.ReadKey();
    }
}

当在没有/优化标志的情况下编译时，它输出的任何CPU配置都如下（生成的IL似乎是一个不可靠的出价）：

result: 0

当使用/优化标志编译时，它正确地输出：

This code is never reached!
result: 1234,56789

为什么会这样？

PS：如果范围检查被注释掉（If（（offset…）），则它将再次输出正确的结果。

EDIT：这是为ReadDouble（）函数生成的IL，请注意没有Console。WriteLine

.method public hidebysig static 
    float64 ReadDouble (
        int32 offset
    ) cil managed 
{
    // Method begins at RVA 0x2060
    // Code size 81 (0x51)
    .maxstack 2
    .locals init (
        [0] float64 'value',
        [1] bool,
        [2] float64,
        [3] uint8& pinned pBuffer,
        [4] uint8[]
    )
    IL_0000: nop
    IL_0001: ldarg.0
    IL_0002: ldc.i4.8
    IL_0003: add
    IL_0004: ldsfld uint8[] WeirdBug.Program::fData
    IL_0009: ldlen
    IL_000a: conv.i4
    IL_000b: cgt
    IL_000d: ldc.i4.0
    IL_000e: ceq
    IL_0010: stloc.1
    IL_0011: ldloc.1
    IL_0012: brtrue.s IL_0020
    IL_0014: ldc.r8 0.0
    IL_001d: stloc.2
    IL_001e: br.s IL_004f
    IL_0020: ldc.r8 0.0
    IL_0029: stloc.0
    IL_002a: ldsfld uint8[] WeirdBug.Program::fData
    IL_002f: dup
    IL_0030: stloc.s 4
    IL_0032: brfalse.s IL_003a
    IL_0034: ldloc.s 4
    IL_0036: ldlen
    IL_0037: conv.i4
    IL_0038: brtrue.s IL_003f
    IL_003a: ldc.i4.0
    IL_003b: conv.u
    IL_003c: stloc.3
    IL_003d: br.s IL_0048
    IL_003f: ldloc.s 4
    IL_0041: ldc.i4.0
    IL_0042: ldelema [mscorlib]System.Byte
    IL_0047: stloc.3
    IL_0048: ldloc.3
    IL_0049: conv.i
    IL_004a: ldind.r8
    IL_004b: stloc.0
    IL_004c: ldc.i4.0
    IL_004d: conv.u
    IL_004e: stloc.3
    IL_004f: ldloc.2
    IL_0050: ret
}