[llvm] [GVNSink] Avoid repeated hash lookups (NFC) (PR #113023)

[Nikita Popov via llvm-commits]

================
@@ -535,14 +535,10 @@ class ValueTable {
     uint32_t e = ExpressionNumbering[exp];
     if (!e) {
       hash_code H = exp->getHashValue([=](Value *V) { return lookupOrAdd(V); });
-      auto I = HashNumbering.find(H);
-      if (I != HashNumbering.end()) {
-        e = I->second;
-      } else {
-        e = nextValueNumber++;
-        HashNumbering[H] = e;
-        ExpressionNumbering[exp] = e;
-      }
+      auto [I, Inserted] = HashNumbering.try_emplace(H, nextValueNumber + 1);
----------------
nikic wrote:

Shouldn't this be?
```suggestion
      auto [I, Inserted] = HashNumbering.try_emplace(H, nextValueNumber);
```
The old code is using the result of post-inc, which is the pre-increment value.

https://github.com/llvm/llvm-project/pull/113023