[llvm] [LoongArch] Pre-commit tests for absolute difference (PR #132898)

[Lu Weining via llvm-commits]

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@@ -0,0 +1,557 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN: llc -mtriple=loongarch64 -mattr=+lasx < %s | FileCheck %s
+
+;; TODO: Currently LoongArch generates sub-optimal code for these cases
+;; 1. trunc(abs(sub(sext(a),sext(b)))) -> abds(a,b) or abdu(a,b)
+;; 2. abs(sub_nsw(x, y)) -> abds(a,b)
+;; 3. sub(smax(a,b),smin(a,b)) -> abds(a,b) or abdu(a,b)
+;; 4. select(icmp(a,b),sub(a,b),sub(b,a)) -> abds(a,b) or abdu(a,b)
----------------
SixWeining wrote:

```suggestion
;; 4. select(icmp(a,b, slt|ult),sub(a,b),sub(b,a)) -> abds(a,b) or abdu(a,b)
```

https://github.com/llvm/llvm-project/pull/132898