[英]Why didn't -O3 GCC Optimization inline this function?
In GCC compiler, whenever -O3 is flagged, the compiler optimizes mainly by Loop Unrolling and Function Inlining. 在GCC编译器中,每当标记-O3时,编译器主要通过循环展开和函数内联进行优化。
However, when I compiled an application that has the following function, it didn't do Function Inlining. 但是,当我编译具有以下功能的应用程序时,它没有执行函数内联。 From gprofing and gconving I could notice that this function (comp_t_delay) was not called from the main function unit of this application.
从gprofing和gconving我可以注意到这个函数(comp_t_delay)没有从这个应用程序的主功能单元调用。 However, it was called from a function, called by a function, called by the main function.
但是,它是由函数调用的函数调用的,由main函数调用。
Here is the code of comp_t_delay(int in,int ip) that I want to know why the GCC didn't optimize it using -O3 (any help is appreciated!): 这是comp_t_delay(int in,int ip)的代码,我想知道为什么GCC没有使用-O3优化它(任何帮助都很感激!):
static float
comp_t_delay(int in,int ip)
{
int sb, sib,dx, dy;
t_type_ptr st, sit;
float d_ssi;
d_ssi = 0.;
sb = net[in].node_block[0];
st = block[sb].type;
sib = net[in].node_block[ip];
sit = block[sib].type;
assert(st != NULL);
assert(sit != NULL);
dx = abs(block[sib].x - block[sb].x);
dy = abs(block[sib].y - block[sb].y);
if(st == T_IO)
{
if(sit == T_IO)
d_ssi = de_io[dx][dy];
else
d_ssi = de_iof[dx][dy];
}
else
{
if(sit == T_IO)
d_ssi = de_fio[dx][dy];
else
d_ssi = de_fb[dx][dy];
}
if(d_ssi < 0)
{
printf
("Error1\n");
exit(1);
}
if(d_ssi < 0.)
{
printf
("Error2\n");
exit(1);
}
return (d_ssi);
}
It most probably didn't inline it because it is too long. 它很可能没有内联它,因为它太长了。 Long functions, when inlined, can actually cause the code to run slower - for example you get the CPU registers bloated by more variables.
内联时,长函数实际上可能导致代码运行速度变慢 - 例如,CPU寄存器会因更多变量而膨胀。 In this particular case gcc decided it will be faster not to inline the function.
在这种特殊情况下,gcc决定不更新内联函数。
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