[PATCH] D18998: [CodeGen] Explicitly widen non-power-of-2 vector HFA base types.

[Ahmed Bougacha via cfe-commits]

ab created this revision.
ab added reviewers: rjmccall, uweigand, t.p.northover.
ab added a subscriber: cfe-commits.
Herald added a subscriber: aemerson.

Currently, for the ppc64--gnu and aarch64 ABIs, we recognize:


```
typedef __attribute__((__ext_vector_type__(3))) float v3f32;
typedef __attribute__((__ext_vector_type__(16))) char v16i8;

struct HFA {
  v3f32 a;
  v16i8 b;
};

```

as an HFA.  Since the base type is the first type encountered, we pass the HFA as:

    [2 x <3 x float>]

Which leads to incorrect IR (relying on padding values) when the second field is used.

This patch teaches isHomogeneousAggregate to explicitly uses the widened vector (after size rounding).


I don't know if this approach is either sufficient or ideal; alternatives I considered:
- pass as [2 x <3 x float>], but bitcast the struct pointer itself to [2 x <4 x float>]*;  this still relies on accessing padding.
- return an llvm::Type (instead of QualType) in isHomogeneousAggregate: there are a couple callers that rely on size/alignment info which should come from the clang::Type.
- reject non-power-of-2 vectors as HFA base types: this doesn't make sense, as we treat them everywhere else as the next-power-of-2 type.
- fixup the base type in the various isHomogeneousAggregate callers: repetitive changes all over the place.

http://reviews.llvm.org/D18998

Files:
  lib/CodeGen/TargetInfo.cpp
  test/CodeGen/aarch64-arguments-hfa-v3.c
  test/CodeGen/arm64-arguments.c
  test/CodeGen/ppc64le-aggregates.c

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