变量比较
以下 C# 代码片段:
var x = 1;
var y = 1;
if (x == y)
Console.Write("True");
生成此 MSIL:
.locals init (
[0] int32 x,
[1] int32 y,
[2] bool CS$4$0000)
L_0000: nop
L_0001: ldc.i4.1
L_0002: stloc.0
L_0003: ldc.i4.1
L_0004: stloc.1
L_0005: ldloc.0
L_0006: ldloc.1
L_0007: ceq
L_0009: ldc.i4.0
L_000a: ceq
L_000c: stloc.2
L_000d: ldloc.2
L_000e: brtrue.s L_001b
L_0010: ldstr "True"
L_0015: call void [mscorlib]System.Console::Write(string)
L_001a: nop
L_001b: ret
为什么有两个 ceq
调用?
谢谢
The following C#-snippet:
var x = 1;
var y = 1;
if (x == y)
Console.Write("True");
Generates this MSIL:
.locals init (
[0] int32 x,
[1] int32 y,
[2] bool CS$4$0000)
L_0000: nop
L_0001: ldc.i4.1
L_0002: stloc.0
L_0003: ldc.i4.1
L_0004: stloc.1
L_0005: ldloc.0
L_0006: ldloc.1
L_0007: ceq
L_0009: ldc.i4.0
L_000a: ceq
L_000c: stloc.2
L_000d: ldloc.2
L_000e: brtrue.s L_001b
L_0010: ldstr "True"
L_0015: call void [mscorlib]System.Console::Write(string)
L_001a: nop
L_001b: ret
Why is there two ceq
calls?
Thanks
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第二个
ceq
操作码将第一个操作码的结果与0
进行比较。 (false
)然后将此结果放入一个变量中,从该变量加载,如果为
true
,则跳过WriteLine
调用。我认为发布模式会生成更高效的代码,但我懒得检查。
The second
ceq
opcode compares the result of the first one to0
. (false
)This result is then put in a variable, loaded from the variable, and, if it was
true
, theWriteLine
call is skipped.I would assume that Release mode generates more efficient code, but I'm too lazy to check.
关于与
ceq
进行比较来自 MSDN:第二个
ceq
检查第一次比较是否失败,如果失败,则跳转到退出点。About comparing values with
ceq
From MSDN:The second
ceq
checks whether the first comparison failed, if so, it jumps to the exit point.