Mapping access with multi-slot keys.

test/libsolidity/semanticTests/storage/mapping_string_key.sol

@@ -0,0 +1,24 @@
+contract C {
+    mapping (string => uint) m_nameToRecord;
+    function set(string calldata key, uint value) external {
+        m_nameToRecord[key] = value;
+    }
+    function get(string calldata key) external view returns (uint) {
+        return m_nameToRecord[key];
+    }
+    function setFixed(uint value) external {
+        m_nameToRecord["fixed"] = value;
+    }
+    function getFixed() external view returns (uint) {
+        return m_nameToRecord["fixed"];
+    }
+}
+// ====
+// compileViaYul: also
+// ----
+// set(string,uint256): 0x40, 8, 3, "abc" ->
+// get(string): 0x20, 3, "abc" -> 8
+// get(string): 0x20, 3, "abe" -> 0
+// getFixed() -> 0
+// setFixed(uint256): 9 ->
+// getFixed() -> 9