Fix a miscompilation in const slotting and result relinking

Author: kateinoigakukun

FuzzTesting/FailCases/FuzzDifferential/diff-68883.wasm

@@ -1636,6 +1636,7 @@ struct InstructionTranslator<Context: TranslatorContext>: InstructionVisitor {
     private mutating func visitConst(_ type: ValueType, _ value: Value) {
         if let constSlotIndex = constantSlots.allocate(value) {
             valueStack.pushConst(constSlotIndex, type: type)
+            iseqBuilder.resetLastEmission()
             return
         }
         let value = UntypedValue(value)

Sources/WasmKit/Translator.swift

@@ -1,5 +1,5 @@
 (module
-  (func (export "check") (param i32) (result i32)
+  (func (export "check-limit") (param i32) (result i32)
     ;; Enough to reach the limit of constant slots
     (drop (i32.const 1))
     (drop (i32.const 2))
@@ -9,7 +9,18 @@
     (drop (i32.const 6))
     (i32.add (local.get 0) (i32.add (i32.const 1) (i32.const 1)))
   )
+  (func (export "invalidate-relink") (result i32)
+      (local i32)
+      (i32.add (i32.const 1) (i32.const 1))
+      ;; This constant should invalidate the relinking
+      ;; connection of i32.add even though it doesn't
+      ;; emit its own instruction.
+      (i32.const 0)
+      (local.set 0)
+      (local.get 0)
+  )
 )
 
-(assert_return (invoke "check" (i32.const 3)) (i32.const 5))
+(assert_return (invoke "check-limit" (i32.const 3)) (i32.const 5))
+(assert_return (invoke "invalidate-relink") (i32.const 0))