[all-commits] [llvm/llvm-project] e59f02: [GlobalISel] Translate <1 x N> getelementptrs to s...

[Jessica Paquette via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: e59f02216f1c6972925c5ef0f1df6d434c652c69
      https://github.com/llvm/llvm-project/commit/e59f02216f1c6972925c5ef0f1df6d434c652c69
  Author: Jessica Paquette <jpaquette at apple.com>
  Date:   2021-07-01 (Thu, 01 Jul 2021)

  Changed paths:
    M llvm/lib/CodeGen/GlobalISel/IRTranslator.cpp
    A llvm/test/CodeGen/AArch64/GlobalISel/irtranslator-one-by-n-vector-ptr-add.ll

  Log Message:
  -----------
  [GlobalISel] Translate <1 x N> getelementptrs to scalar G_PTR_ADDs

In `IRTranslator::translateGetElementPtr`, when we run into a vector gep with
some scalar operands, we try to normalize those operands using
`buildSplatVector`.

This is fine except for when the getelementptr has a <1 x N> type. In that case
it is treated as a scalar. If we run into one of these then every call to

```
// With VectorWidth = 1
LLT::fixed_vector(VectorWidth, PtrTy)
```

will assert.

Here's an example (equivalent to the added testcase):
https://godbolt.org/z/hGsTnMYdW

To get around this, this patch adds a variable, `WantSplatVector`, which
is true when our vector type ought to actually be represented using a vector.
When it's false, we'll translate as a scalar. This checks if `VectorWidth > 1`.

This fixes this bug:
https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=35496

Differential Revision: https://reviews.llvm.org/D105316