OptimizeInstructions: Use fallthrough for (unsigned)x < 0 ==> i32(0) (#7480)

Fixes: #7455

Author: xuruiyang2002

src/passes/OptimizeInstructions.cpp

@@ -570,11 +570,13 @@ struct OptimizeInstructions
           return replaceCurrent(getDroppedChildrenAndAppend(curr, c));
         }
         // unsigned(x) < 0   =>   i32(0)
-        if (matches(curr, binary(LtU, any(&x), ival(&c))) &&
+        if (curr->op == Abstract::getBinary(curr->left->type, Abstract::LtU) &&
+            (c = getFallthrough(curr->right)->dynCast<Const>()) &&
             c->value.isZero()) {
-          c->value = Literal::makeZero(Type::i32);
-          c->type = Type::i32;
-          return replaceCurrent(getDroppedChildrenAndAppend(curr, c));
+          // We could reuse c here, if we checked it had no more uses
+          auto zero =
+            Builder(*getModule()).makeConst(Literal::makeZero(Type::i32));
+          return replaceCurrent(getDroppedChildrenAndAppend(curr, zero));
         }
       }
     }

test/lit/passes/optimize-instructions-mvp.wast

@@ -175,6 +175,7 @@
       )
     )
   )
+
   ;; CHECK:      (func $eqz-gt_s (result i32)
   ;; CHECK-NEXT:  (i32.eqz
   ;; CHECK-NEXT:   (i32.const 0)
@@ -11575,6 +11576,44 @@
   ;; CHECK-NEXT:   )
   ;; CHECK-NEXT:  )
   ;; CHECK-NEXT:  (drop
+  ;; CHECK-NEXT:   (block (result i32)
+  ;; CHECK-NEXT:    (drop
+  ;; CHECK-NEXT:     (i32.load
+  ;; CHECK-NEXT:      (i32.const 0)
+  ;; CHECK-NEXT:     )
+  ;; CHECK-NEXT:    )
+  ;; CHECK-NEXT:    (drop
+  ;; CHECK-NEXT:     (block (result i32)
+  ;; CHECK-NEXT:      (i32.store
+  ;; CHECK-NEXT:       (i32.const 0)
+  ;; CHECK-NEXT:       (i32.const 0)
+  ;; CHECK-NEXT:      )
+  ;; CHECK-NEXT:      (i32.const 0)
+  ;; CHECK-NEXT:     )
+  ;; CHECK-NEXT:    )
+  ;; CHECK-NEXT:    (i32.const 0)
+  ;; CHECK-NEXT:   )
+  ;; CHECK-NEXT:  )
+  ;; CHECK-NEXT:  (drop
+  ;; CHECK-NEXT:   (block (result i32)
+  ;; CHECK-NEXT:    (drop
+  ;; CHECK-NEXT:     (i64.load
+  ;; CHECK-NEXT:      (i32.const 0)
+  ;; CHECK-NEXT:     )
+  ;; CHECK-NEXT:    )
+  ;; CHECK-NEXT:    (drop
+  ;; CHECK-NEXT:     (block (result i64)
+  ;; CHECK-NEXT:      (i64.store
+  ;; CHECK-NEXT:       (i32.const 0)
+  ;; CHECK-NEXT:       (i64.const 0)
+  ;; CHECK-NEXT:      )
+  ;; CHECK-NEXT:      (i64.const 0)
+  ;; CHECK-NEXT:     )
+  ;; CHECK-NEXT:    )
+  ;; CHECK-NEXT:    (i32.const 0)
+  ;; CHECK-NEXT:   )
+  ;; CHECK-NEXT:  )
+  ;; CHECK-NEXT:  (drop
   ;; CHECK-NEXT:   (i32.ne
   ;; CHECK-NEXT:    (local.get $x)
   ;; CHECK-NEXT:    (i32.const 0)
@@ -11867,6 +11906,33 @@
       )
       (i64.const 0)
     ))
+    (drop (i32.lt_u
+        (i32.load
+          (i32.const 0)
+        )
+        (block (result i32)
+          (i32.store
+            (i32.const 0)
+            (i32.const 0)
+          )
+          (i32.const 0)
+        )
+      )
+    )
+    (drop (i64.lt_u
+        (i64.load
+          (i32.const 0)
+        )
+        (block (result i64)
+          (i64.store
+            (i32.const 0)
+            (i64.const 0)
+          )
+          (i64.const 0)
+        )
+      )
+    )
+
 
     ;; (unsigned)x > 0  =>  x != 0
     (drop (i32.gt_u