就像我的头文件是：
class A
{
void Complicated();
}
和我的源文件
void A::Complicated()
{
...really long function...
}
我可以将源文件拆分成
void DoInitialStuff(pass necessary vars by ref or value)
{
...
}
void HandleCaseA(pass necessary vars by ref or value)
{
...
}
void HandleCaseB(pass necessary vars by ref or value)
{
...
}
void FinishUp(pass necessary vars by ref or value)
{
...
}
void A::Complicated()
{
...
DoInitialStuff(...);
switch ...
HandleCaseA(...)
HandleCaseB(...)
...
FinishUp(...)
}
完全可以阅读,不用担心影响性能？
解决方法
您应该将函数标记为静态,以便编译器知道它们是该翻译单元的本地.
没有静态编译器不能假设(禁止LTO / WPA)该函数只调用一次,因此不太可能内联它.
演示使用LLVM Try Out页.
也就是说,首先可读性的代码,微优化(和这样的调整是微优化)只能在性能测量之后才会出现.
例：
#include <cstdio> static void foo(int i) { int m = i % 3; printf("%d %d",i,m); } int main(int argc,char* argv[]) { for (int i = 0; i != argc; ++i) { foo(i); } }
产生静态：
; ModuleID = '/tmp/webcompile/_27689_0.bc'
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"
target triple = "x86_64-unknown-linux-gnu"
@.str = private constant [6 x i8] c"%d %d\00" ; <[6 x i8]*> [#uses=1]
define i32 @main(i32 %argc,i8** nocapture %argv) nounwind {
entry:
%cmp4 = icmp eq i32 %argc,0 ; <i1> [#uses=1]
br i1 %cmp4,label %for.end,label %for.body
for.body: ; preds = %for.body,%entry
%0 = phi i32 [ %inc,%for.body ],[ 0,%entry ] ; <i32> [#uses=3]
%rem.i = srem i32 %0,3 ; <i32> [#uses=1]
%call.i = tail call i32 (i8*,...)* @printf(i8* getelementptr inbounds ([6 x i8]* @.str,i64 0,i64 0),i32 %0,i32 %rem.i) nounwind ; <i32> [#uses=0]
%inc = add nsw i32 %0,1 ; <i32> [#uses=2]
%exitcond = icmp eq i32 %inc,%argc ; <i1> [#uses=1]
br i1 %exitcond,label %for.body
for.end: ; preds = %for.body,%entry
ret i32 0
}
declare i32 @printf(i8* nocapture,...) nounwind
没有静态：
; ModuleID = '/tmp/webcompile/_27859_0.bc'
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"
target triple = "x86_64-unknown-linux-gnu"
@.str = private constant [6 x i8] c"%d %d\00" ; <[6 x i8]*> [#uses=1]
define void @foo(int)(i32 %i) nounwind {
entry:
%rem = srem i32 %i,3 ; <i32> [#uses=1]
%call = tail call i32 (i8*,i32 %i,i32 %rem) ; <i32> [#uses=0]
ret void
}
declare i32 @printf(i8* nocapture,...) nounwind
define i32 @main(i32 %argc,%entry
ret i32 0
}
