wrong-copy.c

// -fstrict-aliasing -Wall -Wextra -Werror -pedantic -std=c99

#include <string.h>
#include <stdio.h>

#define ARRAY_COPY(dst, src, len) {\
		struct {\
			struct {\
				char __[len];\
			} *__s, *__d;\
		} __cp = { .__s = (void*)(src), .__d = (void*)(dst) };\
		*(__cp.__d) = *(__cp.__s);\
	}

void s1() __attribute__((optimize(2)));
void s1()
{
	int src[10] = { 10, 20, 30, 40, 50, 60, 70, 80, 90, 100 };
	int *dst = src + 2;

	ARRAY_COPY(dst, src, sizeof(int)*8);

	printf("%d %d %d %d %d %d %d %d %d %d\n", src[0], src[1], src[2], src[3],
		src[4], src[5], src[6], src[7], src[8], src[9]);
}

void s2() __attribute__((optimize(0)));
void s2()
{
	int src[10] = { 10, 20, 30, 40, 50, 60, 70, 80, 90, 100 };
	int *dst = src + 2;

	ARRAY_COPY(dst, src, sizeof(int)*8);

	printf("%d %d %d %d %d %d %d %d %d %d\n", src[0], src[1], src[2], src[3],
		src[4], src[5], src[6], src[7], src[8], src[9]);
}

void s3() __attribute__((optimize(3)));
void s3()
{
	int src[10] = { 10, 20, 30, 40, 50, 60, 70, 80, 90, 100 };
	int *dst = src + 2;

	memmove(dst, src, sizeof(int)*8);

	printf("%d %d %d %d %d %d %d %d %d %d\n", src[0], src[1], src[2], src[3],
		src[4], src[5], src[6], src[7], src[8], src[9]);
}

int main(int argc, char **argv)
{
	(void) argc;
	(void) argv;
	s1();
	s2();
	s3();
	return 0;
}