[all-commits] [llvm/llvm-project] 8a9921: [AArch64] Use INDEX for constant Neon step vectors...

[Ricardo Jesus via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 8a9921f5692ab33451d11454b40a023ca0965a69
      https://github.com/llvm/llvm-project/commit/8a9921f5692ab33451d11454b40a023ca0965a69
  Author: Ricardo Jesus <rjj at nvidia.com>
  Date:   2024-10-23 (Wed, 23 Oct 2024)

  Changed paths:
    M llvm/lib/Target/AArch64/AArch64ISelLowering.cpp
    M llvm/test/CodeGen/AArch64/active_lane_mask.ll
    A llvm/test/CodeGen/AArch64/sve-index-const-step-vector.ll

  Log Message:
  -----------
  [AArch64] Use INDEX for constant Neon step vectors (#113424)

When compiling for an SVE target we can use INDEX to generate constant
fixed-length step vectors, e.g.:
```
uint32x4_t foo() {
  return (uint32x4_t){0, 1, 2, 3};
}
```
Currently:
```
foo():
        adrp    x8, .LCPI1_0
        ldr     q0, [x8, :lo12:.LCPI1_0]
        ret
```
With INDEX:
```
foo():
        index   z0.s, #0, #1
        ret
```

The logic for this was already in `LowerBUILD_VECTOR`, though it was
hidden under a check for `!Subtarget->isNeonAvailable()`. This patch
refactors this to enable the corresponding code path unconditionally for
constant step vectors (as long as we can use SVE for them).



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