[llvm] [AArch64] Support lowering smaller than legal LOOP_DEP_MASKs to whilewr/rw (PR #171982)

Fri Dec 12 02:11:42 PST 2025

llvmbot wrote:

<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-backend-aarch64

Author: Benjamin Maxwell (MacDue)

<details>
<summary>Changes</summary>

This adds support for lowering smaller-than-legal masks such as:

```
<vscale x 8 x i1> @<!-- -->llvm.loop.dependence.war.mask.nxv8i1(ptr %a, ptr %b, i64 1)
```

To a whilewr + unpack. It also slightly simplifies the lowering.

---
Full diff: https://github.com/llvm/llvm-project/pull/171982.diff

2 Files Affected:

- (modified) llvm/lib/Target/AArch64/AArch64ISelLowering.cpp (+28-40) 
- (modified) llvm/test/CodeGen/AArch64/alias_mask_scalable.ll (+35) 

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</details>

https://github.com/llvm/llvm-project/pull/171982