[llvm] [GlobalISel] Add computeNumSignBits for ASHR (PR #139503)

[Matt Arsenault via llvm-commits]

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@@ -0,0 +1,109 @@
+# NOTE: Assertions have been autogenerated by utils/update_givaluetracking_test_checks.py UTC_ARGS: --version 5
+# RUN: llc -mtriple aarch64 -passes="print<gisel-value-tracking>" %s -o - 2>&1 | FileCheck %s
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arsenm wrote:

```suggestion
# RUN: llc -mtriple aarch64 -passes='print<gisel-value-tracking>' %s -filetype=null 2>&1 | FileCheck %s
```

Not using stdout? 

https://github.com/llvm/llvm-project/pull/139503