#include <stdint.h> #include <string.h> typedef struct { int32_t a; int32_t b; } Foo; int main(void) { uint8_t array[1024];

#include <stdint.h> #include <string.h> typedef struct { int32_t a; int32_t b; } Foo; int main(void) { uint8_t array[1024]; memset(array, 1, sizeof(array)); Foo *foo = (Foo*)(&array[0]); foo->a += 1; } Using clang 3.8.0-2. Compiling examples with `clang -S llvm-ir`. It appears that the array is aligned with the minimum ABI requirement 16 by default? May be a note of this in the standard, can't recall of the top of my head. %array = alloca [1024 x i8], align 16 ... %6 = load i32, i32* %5, align 4 ... store i32 %7, i32* %5, align 4 We can also explicitly specify the alignment required in C11. #include <stdalign.h> #include <stdint.h> #include <string.h> typedef struct { int32_t a; int32_t b; } Foo; int main(void) { uint8_t alignas(alignof(Foo)) array[1024]; memset(array, 1, sizeof(array)); Foo *foo = (Foo*)(&array[0]); foo->a += 1; } Results in the following IR. %array = alloca [1024 x i8], align 4 ... %6 = load i32, i32* %5, align 4 ... store i32 %7, i32* %5, align 4