llvm dev - Apr 2018 - Does an array and homogeneous struct have the same layout?

Does an array of a value type and a structure containing only that type
have the same alignment requirements?  That is, in C-syntax:

float* array;

struct point { float x; float y; }
point p;

array = (float*)&p;


Does `array[0]` now refer to x, and `array[1]` to y?

I'm creating these structures in LLVM with default packing
(StructType::isPacked == false). I have a library that takes simple
arrays for point structs (OpenGL) and would like to layer nicer types on
top. I'm reasonably certain the above holds true, but want to
double-check that it's guaranteed.

I'd also be doing this type of operation to refer to a list of points:

point* p = ...;
array = (float*)p;


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edA-qa mort-ora-y  
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On 8 April 2018 at 10:46, edA-qa mort-ora-y via llvm-dev
<llvm-dev at lists.llvm.org> wrote:
> Does an array of a value type and a structure containing only that type
> have the same alignment requirements?  That is, in C-syntax:
Yes, they're both derived from the DataLayout in a way that targets
cannot override.
> Does `array[0]` now refer to x, and `array[1]` to y?
Aside from array[1] being undefined behaviour n C, yes. The equivalent
is fine in LLVM of course, where types are punned merrily.

Cheers.

Tim.