为什么这些方法会使我的程序变得更大？

Question

I'm working on some Arduino code and have the following code:

uint8_t world[24][2][3];
bool getDispPixel(uint8_t x, uint8_t y, uint8_t num)
{
    static uint8_t rowByte = 0; // 0 means top 8, 1 means bottom 8
    static uint8_t rowBit = 0;

    if(y > 7)
    {
        rowByte = 1;
        rowBit = x - 8;
    }
    else
    {
        rowByte = 0;
        rowBit = x;
    }

    return (world[x][rowByte][num] & (1 << rowBit)) > 0;
}

void setDispPixel(uint8_t x, uint8_t y, uint8_t num, bool state)
{
    static uint8_t rowByte = 0; // 0 means top 8, 1 means bottom 8
    static uint8_t rowBit = 0;

    if(y > 7)
    {
        rowByte = 1;
        rowBit = x - 8;
    }
    else
    {
        rowByte = 0;
        rowBit = x;
    }

    if(state)
        world[x][rowByte][num] |= (1 << rowBit);
    else
        world[x][rowByte][num] &= ~(1 << rowBit);
}

What's weird is these methods add a TON of size to the program. Even just parts of it. If i comment out the following part from just one of the methods, it drops 2536 bytes from the program size!

if(y > 7)
{
    rowByte = 1;
    rowBit = x - 8;
}
else
{
    rowByte = 0;
    rowBit = x;
}

Both methods are called quite often, over 200 times combined. I would believe it if they were marked as inline, but they are not. Any idea of what could be causing this?

Update: If I completely comment out those methods' contents it drops the size by 20k! Looks like every call to the function eats up 94 bytes. No idea why...

Answer 1

If the Arduino toolchain supports GCC extensions (and some quick searching suggests it does), then you can use __attribute__((noinline)) to disable inlining on these functions like so:

bool getDispPixel(uint8_t x, uint8_t y, uint8_t num) __attribute__((noinline));
bool getDispPixel(uint8_t x, uint8_t y, uint8_t num)
{
    // body of the function here
}

void setDispPixel(uint8_t x, uint8_t y, uint8_t num, bool state) __attribute((noinline));
void setDispPixel(uint8_t x, uint8_t y, uint8_t num, bool state)
{
    // body of the function here
}

The extra line looks redundant, but isn't. It's how the syntax for the extension works.

Answer 2

Here is the output of: nm --print-size --size-sort --radix=d --demangle GOLClock.cpp.o (Size of your objects ranked by size):

http://pastebin.com/rHEhuEKg

You can see that the assembly code for the function SetDispPixel takes 148 bytes, and for the function GetDispPixel 94 bytes.

If it causes a huge increase of your binary it probably means that your function is getting inlined.