Merge pull request #11763 from ethereum/basefee-hasOpcode

Allow basefee as Yul identifier for EVMVersion < london

test/libsolidity/semanticTests/inlineAssembly/basefee_berlin_function.sol

@@ -0,0 +1,22 @@
+contract C {
+    function f() public view returns (uint ret) {
+        assembly {
+            let basefee := sload(0)
+            ret := basefee
+        }
+    }
+    function g() public pure returns (uint ret) {
+        assembly {
+            function basefee() -> r {
+                r := 1000
+            }
+            ret := basefee()
+        }
+    }
+}
+// ====
+// compileViaYul: also
+// EVMVersion: <=berlin
+// ----
+// f() -> 0
+// g() -> 1000

test/libsolidity/syntaxTests/inlineAssembly/basefee_reserved_london.sol

@@ -0,0 +1,12 @@
+contract C {
+    function f() public view returns (uint ret) {
+        assembly {
+            let basefee := sload(0)
+            ret := basefee
+        }
+    }
+}
+// ====
+// EVMVersion: =london
+// ----
+// ParserError 5568: (98-105): Cannot use builtin function name "basefee" as identifier name.

test/libsolidity/syntaxTests/types/magic_block_basefee_error.sol

@@ -2,14 +2,8 @@ contract C {
     function f() public view returns (uint) {
         return block.basefee;
     }
-    function g() public view returns (uint ret) {
-        assembly {
-            ret := basefee()
-        }
-    }
 }
 // ====
-// EVMVersion: =berlin
+// EVMVersion: <=berlin
 // ----
 // TypeError 5921: (74-87): "basefee" is not supported by the VM version.
-// TypeError 5430: (183-190): The "basefee" instruction is only available for London-compatible VMs (you are currently compiling for "berlin").