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

Author: kazutakahirata

llvm/lib/Transforms/Scalar/GVNSink.cpp

@@ -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);
+      e = I->second;
+      if (Inserted)
+        ExpressionNumbering[exp] = nextValueNumber++;
     }
     ValueNumbering[V] = e;
     return e;