Some tests.

test/libsolidity/semanticTests/modifiers/many_simple.sol

@@ -0,0 +1,24 @@
+contract C {
+    uint256 public x;
+    modifier m() {
+        x ++;
+        _;
+    }
+
+    modifier mdouble() {
+        _;
+        _;
+    }
+
+    function f() public m m m m m m m m m m mdouble m m m m m m m m m m m m m m m m returns (uint) {
+        return x;
+    }
+}
+
+// ====
+// compileToEwasm: also
+// compileViaYul: also
+// ----
+// x() -> 0
+// f() -> 0x2a
+// x() -> 0x2a

test/libsolidity/semanticTests/modifiers/simple_and_nonsimple_modifier.sol

@@ -0,0 +1,26 @@
+contract C {
+    uint256 public x;
+    modifier m1() {
+        x = 1;
+        _;
+    }
+
+    modifier m2(bool abort) {
+        if (abort) return;
+        _;
+    }
+
+    function f(bool abort) public m1 m2(abort) {
+        x += 2;
+    }
+}
+
+// ====
+// compileToEwasm: also
+// compileViaYul: also
+// ----
+// x() -> 0
+// f(bool): false ->
+// x() -> 3
+// f(bool): true ->
+// x() -> 1