[llvm] Revert "[APInt] Remove multiplicativeInverse with explicit modulus (#… (PR #87812)

[Jay Foad via llvm-commits]

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@@ -1240,6 +1240,55 @@ APInt APInt::sqrt() const {
   return x_old + 1;
 }
 
+/// Computes the multiplicative inverse of this APInt for a given modulo. The
+/// iterative extended Euclidean algorithm is used to solve for this value,
+/// however we simplify it to speed up calculating only the inverse, and take
+/// advantage of div+rem calculations. We also use some tricks to avoid copying
+/// (potentially large) APInts around.
+/// WARNING: a value of '0' may be returned,
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jayfoad wrote:

This comment seems alarmist. I would prefer "Computes the multiplicative inverse of this APInt for a given modulus, or 0 if no such inverse exists."

https://github.com/llvm/llvm-project/pull/87812