[llvm] [ADT] Add implementations for mulhs and mulhu to APInt (PR #84609)

[Jakub Kuderski via llvm-commits]

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@@ -537,19 +537,13 @@ TEST(KnownBitsTest, BinaryExhaustive) {
       [](const KnownBits &Known1, const KnownBits &Known2) {
         return KnownBits::mulhs(Known1, Known2);
       },
-      [](const APInt &N1, const APInt &N2) {
-        unsigned Bits = N1.getBitWidth();
-        return (N1.sext(2 * Bits) * N2.sext(2 * Bits)).extractBits(Bits, Bits);
-      },
+      [](const APInt &N1, const APInt &N2) { return APIntOps::mulhs(N1, N2); },
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kuhar wrote:

Could these be:
```suggestion
      &APIntOps::mulhs,
```
?

https://github.com/llvm/llvm-project/pull/84609