Hi,
Here is our Developer's comments on this issue:
The Intel clang compiler is more strict on pointer types than other compilers, it's a combination of the clang type implementation, plus the aggressive optimizations that the compiler backend tries to do.
In particular, this reinterpretation of the char array pad[] to integer type, doesn't meet the "strict aliasing" requirement for pointers:
bswap_buf((unsigned int *)pad, pwarray, 64);
In general, an object of type "x" needs to be accessed using pointers of type "x".
The exception is that "char *" pointers can safely access any type. The reverse is not true however; integer pointers cannot safely access char-type data.
This article discusses the issue in some detail:
https://stackoverflow.com/questions/52492229/c-byte-array-to-int
Some suggestions:
1) Use the -fno-strict-aliasing flag. This prevents the compiler from making aliasing analysis based on pointer types.
2) Use memcpy as the article suggests:
void bswap_buf (unsigned int *in, unsigned int *out, int len)
{
int i;
for (i=0; i < len /4; i++) {
int val;
memcpy(&val, (void *)&in[i], 4);
out[i] = _byteswap_ulong(val);
}
}
The compiler will not try to use types to analyze memcpy (which is "typeless" with void*).
Please use one of the suggestions and let us know so that we can close this thread.
Thanks,
