[llvm] [APInt] Provide isqrt (floor of square root) instead of sqrt (rounded) (PR #197406)

[Matt Arsenault via llvm-commits]

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@@ -1809,8 +1809,8 @@ class [[nodiscard]] APInt {
     return logBase2();
   }
 
-  /// Compute the square root.
-  LLVM_ABI APInt sqrt() const;
+  /// Compute the floor of the square root of the unsigned value.
+  LLVM_ABI APInt isqrt() const;
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arsenm wrote:

I agree that we should not retain dead code on the off chance of out of tree users 

https://github.com/llvm/llvm-project/pull/197406