g ++生成汇编代码，而没有push和pop

Question

我发现g ++编译器几乎在没有任何push / pop指令的情况下生成汇编代码。它仅在进入/退出功能时使用。每次在堆栈中放置字节时，它都会生成2或3条指令，例如：

load('dataset.mat')

Target_Set=zeros(2,400); %Initialize Target array with 0s

%Set dimensions to resize
h = 50;
w = 45;
imgSize = h*w;

for j=1:4
    for i=1:10
        for k=1:10
            Temp_Struct = struct('im',imresize(handwriting(i,j,k).im,[h,w]));
            n = 100*(j-1) + 10*(i-1) + k;
            P_Set(1:imgSize,n) = reshape(Temp_Struct.im,[imgSize,1]); 

            %Set Target patterns...
            if (j==1) %When character I                   %   Target Patterns...
Line 19========>Target_Set(0,n) = 1;                     %    I   J   K   L
                Target_Set(1,n) = 0;                     %    0   1   0   1
            elseif(j==2) %When character J               %    0   0   1   1
                Target_Set(0,n) = 1;
                Target_Set(1,n)=0;
            elseif(j==3) %When character K            
                Target_Set(0,n) = 0;
                Target_Set(1,n)=1;
            else %When character L       
                Target_Set(0,n) = 1;
                Target_Set(1,n)=1;            
            end;

        end;
    end;
end;

仅安装了movl foo, %eax subl $4, %esp movl %eax, (%esp)` 。有什么理由吗？是更快还是什么？

谢谢。