考虑以下代码:
private static void Main(string[] args)
{
var ar = new double[]
{
100
};
FillTo(ref ar, 5);
Console.WriteLine(string.Join(",", ar.Select(a => a.ToString()).ToArray()));
}
public static void FillTo(ref double[] dd, int N)
{
if (dd.Length >= N)
return;
double[] Old = dd;
double d = double.NaN;
if (Old.Length > 0)
d = Old[0];
dd = new double[N];
for (int i = 0; i < Old.Length; i++)
{
dd[N - Old.Length + i] = Old[i];
}
for (int i = 0; i < N - Old.Length; i++)
dd[i] = d;
}
调试模式下的结果是:100,100,100,100,100。
但在发布模式下它是:100,100,100,100,0。
怎么了?
它使用 .NET Framework 4.7.1 和 .NET Core 2.0.0 进行了测试。
这似乎是一个 JIT 错误;我已经测试过:
// ... existing code unchanged
for (int i = 0; i < N - Old.Length; i++)
{
// Console.WriteLine(i); // <== comment/uncomment this line
dd[i] = d;
}
并添加Console.WriteLine(i)
修复它。 IL 唯一的变化是:
// ...
L_0040: ldc.i4.0
L_0041: stloc.3
L_0042: br.s L_004d
L_0044: ldarg.0
L_0045: ldind.ref
L_0046: ldloc.3
L_0047: ldloc.1
L_0048: stelem.r8
L_0049: ldloc.3
L_004a: ldc.i4.1
L_004b: add
L_004c: stloc.3
L_004d: ldloc.3
L_004e: ldarg.1
L_004f: ldloc.0
L_0050: ldlen
L_0051: conv.i4
L_0052: sub
L_0053: blt.s L_0044
L_0055: ret
vs
// ...
L_0040: ldc.i4.0
L_0041: stloc.3
L_0042: br.s L_0053
L_0044: ldloc.3
L_0045: call void [System.Console]System.Console::WriteLine(int32)
L_004a: ldarg.0
L_004b: ldind.ref
L_004c: ldloc.3
L_004d: ldloc.1
L_004e: stelem.r8
L_004f: ldloc.3
L_0050: ldc.i4.1
L_0051: add
L_0052: stloc.3
L_0053: ldloc.3
L_0054: ldarg.1
L_0055: ldloc.0
L_0056: ldlen
L_0057: conv.i4
L_0058: sub
L_0059: blt.s L_0044
L_005b: ret
看起来完全正确(唯一的区别是额外的ldloc.3
and call void [System.Console]System.Console::WriteLine(int32)
,以及一个不同但等效的目标br.s
).
我怀疑它需要 JIT 修复。
环境:
-
Environment.Version
:4.0.30319.42000
<TargetFramework>netcoreapp2.0</TargetFramework>
- VS:15.5.0 预览版 5.0
-
dotnet --version
: 2.1.1
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