Re-implement unused assign / unused store eliminator.

test/libsolidity/semanticTests/externalContracts/deposit_contract.sol

@@ -176,7 +176,7 @@ contract DepositContract is IDepositContract, ERC165 {
 }
 // ----
 // constructor()
-// gas irOptimized: 1430741
+// gas irOptimized: 1419712
 // gas legacy: 2427905
 // gas legacyOptimized: 1773081
 // supportsInterface(bytes4): 0x0 -> 0

test/libyul/yulOptimizerTests/unusedAssignEliminator/conditionally_assign_before_conditional_revert.yul

@@ -0,0 +1,33 @@
+{
+    function g() {
+        if calldataload(10) { revert(0, 0) }
+    }
+    function f() {
+        let a := calldataload(0)
+        if calldataload(1) {
+            // this can NOT be removed
+            a := 2
+            g()
+        }
+        sstore(0, a)
+    }
+}
+// ----
+// step: unusedAssignEliminator
+//
+// {
+//     function g()
+//     {
+//         if calldataload(10) { revert(0, 0) }
+//     }
+//     function f()
+//     {
+//         let a := calldataload(0)
+//         if calldataload(1)
+//         {
+//             a := 2
+//             g()
+//         }
+//         sstore(0, a)
+//     }
+// }

test/libyul/yulOptimizerTests/unusedAssignEliminator/conditionally_assign_before_leave.yul

@@ -0,0 +1,22 @@
+{
+    function f() {
+        let a := calldataload(0)
+        if calldataload(1) {
+            // this can be removed
+            a := 2
+            leave
+        }
+        sstore(0, a)
+    }
+}
+// ----
+// step: unusedAssignEliminator
+//
+// {
+//     function f()
+//     {
+//         let a := calldataload(0)
+//         if calldataload(1) { leave }
+//         sstore(0, a)
+//     }
+// }

test/libyul/yulOptimizerTests/unusedAssignEliminator/conditionally_assign_before_revert.yul

@@ -0,0 +1,17 @@
+{
+    let a := calldataload(0)
+    if calldataload(1) {
+        // this can be removed
+        a := 2
+        revert(0, 0)
+    }
+    sstore(0, a)
+}
+// ----
+// step: unusedAssignEliminator
+//
+// {
+//     let a := calldataload(0)
+//     if calldataload(1) { revert(0, 0) }
+//     sstore(0, a)
+// }

test/libyul/yulOptimizerTests/unusedAssignEliminator/for_deep_noremove.yul

@@ -46,10 +46,7 @@
 //                         for { } 1 { }
 //                         {
 //                             for { } 1 { a := 10 }
-//                             {
-//                                 b := 12
-//                                 b := 11
-//                             }
+//                             { b := 11 }
 //                         }
 //                     }
 //                 }

test/libyul/yulOptimizerTests/unusedAssignEliminator/revert_after_assign_return.yul

@@ -0,0 +1,35 @@
+{
+    function g() -> x {
+        x := 7
+        if calldataload(0) {
+            x := 3
+            reverting()
+        }
+        if calldataload(1) {
+            x := 3
+            leave
+        }
+        x := 2
+        reverting()
+    }
+    function reverting() { revert(0, 0) }
+    sstore(0, g())
+}
+// ----
+// step: unusedAssignEliminator
+//
+// {
+//     function g() -> x
+//     {
+//         if calldataload(0) { reverting() }
+//         if calldataload(1)
+//         {
+//             x := 3
+//             leave
+//         }
+//         reverting()
+//     }
+//     function reverting()
+//     { revert(0, 0) }
+//     sstore(0, g())
+// }