performance regression on sphereflake

[Rafael Espíndola]

On 18 February 2014 18:20, Renato Golin <renato.golin at linaro.org> wrote:
> Gerolf,
>
> AFAIK, the old APCS never tried to define the alignment of complex
> aggregates, or the stack.
>
> What Rafael said is true, it's more of preference (or rather,
> compatibility), than ABI conformance. But if it's generating
> regressions, we should look into.
>
> Being pragmatic, one has to look why that was set in Clang in the
> first place. Making it the same on both places makes sense (and why
> it's a good idea to have target descriptions external to both LLVM and
> Clang, as proposed by Jim), but we need to make sure whoever added it
> to Clang did it for a reason, and what reason was that.

Good point. I did a git blame and found that the clang datalayout was
changed in r128825 by Bob Wilson, but it looks like he was just
syncing from llvm-gcc.

There might have been a mistake in r128825. llvm-gcc would always just
ask llvm for a datalayout and the ARM Target back then never specified
an 'a' alignment for ARM:

    DataLayout(Subtarget.isAPCS_ABI() ?
               std::string("e-p:32:32-f64:32:64-i64:32:64-"
                           "v128:32:128-v64:32:64-n32") :
               std::string("e-p:32:32-f64:64:64-i64:64:64-"
                           "v128:64:128-v64:64:64-n32")),

Cheers,
Rafael