[PATCH] Implement ADRP CSE for global symbols

[Quentin Colombet]

Hi Jiangning,

> I think you are correct the merged size can't be simply accumulated by indivisual global variable size, because of natural alignment requirement inside the merged data structure.

The size is fine, we accumulate for AllocSize, i.e., with padding and such.
What I meant is the alignment of the whole structure does not look reasonable :).

To be more specific, I think we should set the alignment of the merge structure to DL->getABIAlignment(MergedTy), or something like that.

The example I had in mind was:
@a1 = global i32 align 4
@a2 = global i32 align 4
@a3 = global i32 align 4
@a4 = global i32 align 4
=>
struct MergeGlobal {
 i32, i32, i32, i32
}
With the current approach we would get an alignment of 4*4 = 16, whereas 4 may have been enough. Anyhow, this depends on the data layout.

Thanks for looking into it.

-Quentin

http://reviews.llvm.org/D3432