diff --git a/w2c2/c.c b/w2c2/c.c
index b85b60d..d15ae35 100644
--- a/w2c2/c.c
+++ b/w2c2/c.c
@@ -828,10 +828,8 @@ WARN_UNUSED_RESULT
 wasmCWriteLocalGetExpr(
     const WasmCFunctionWriter* writer
 ) {
-    static const WasmOpcode opcode = wasmOpcodeLocalGet;
-
     WasmLocalInstruction instruction;
-    if (!wasmLocalInstructionRead(writer->code, opcode, &instruction)) {
+    if (!wasmLocalInstructionRead(writer->code, &instruction)) {
         fprintf(stderr, "w2c2: invalid local.get instruction encoding\n");
         return false;
     }
@@ -876,7 +874,7 @@ wasmCWriteLocalAssignmentExpr(
     const WasmOpcode opcode
 ) {
     WasmLocalInstruction instruction;
-    if (!wasmLocalInstructionRead(writer->code, opcode, &instruction)) {
+    if (!wasmLocalInstructionRead(writer->code, &instruction)) {
         fprintf(
             stderr,
             "w2c2: invalid %s instruction encoding\n",
@@ -930,7 +928,7 @@ wasmCWriteGlobalGetExpr(
     static const WasmOpcode opcode = wasmOpcodeGlobalGet;
 
     WasmGlobalInstruction instruction;
-    if (!wasmGlobalInstructionRead(writer->code, opcode, &instruction)) {
+    if (!wasmGlobalInstructionRead(writer->code, &instruction)) {
         fprintf(
             stderr,
             "w2c2: invalid %s instruction encoding\n",
@@ -980,7 +978,7 @@ wasmCWriteGlobalSetExpr(
     static const WasmOpcode opcode = wasmOpcodeGlobalSet;
 
     WasmGlobalInstruction instruction;
-    if (!wasmGlobalInstructionRead(writer->code, opcode, &instruction)) {
+    if (!wasmGlobalInstructionRead(writer->code, &instruction)) {
         fprintf(
             stderr,
             "w2c2: invalid %s instruction encoding\n",
@@ -1131,7 +1129,7 @@ wasmCWriteLoadExpr(
 ) {
     WasmLoadStoreInstruction instruction;
 
-    if (!wasmLoadStoreInstructionRead(writer->code, opcode, &instruction)) {
+    if (!wasmLoadStoreInstructionRead(writer->code, &instruction)) {
         fprintf(stderr, "w2c2: invalid load instruction encoding\n");
         return false;
     }
@@ -1260,7 +1258,7 @@ wasmCWriteStoreExpr(
     const WasmOpcode opcode
 ) {
     WasmLoadStoreInstruction instruction;
-    if (!wasmLoadStoreInstructionRead(writer->code, opcode, &instruction)) {
+    if (!wasmLoadStoreInstructionRead(writer->code, &instruction)) {
         fprintf(stderr, "w2c2: invalid store instruction encoding\n");
         return false;
     }
@@ -1356,10 +1354,8 @@ WARN_UNUSED_RESULT
 wasmCWriteMemorySize(
     const WasmCFunctionWriter* writer
 ) {
-    static const WasmOpcode opcode = wasmOpcodeMemorySize;
-
     WasmMemoryInstruction instruction;
-    if (!wasmMemoryInstructionRead(writer->code, opcode, &instruction)) {
+    if (!wasmMemoryInstructionRead(writer->code, &instruction)) {
         fprintf(stderr, "w2c2: invalid memory.size instruction encoding\n");
         return false;
     }
@@ -1411,10 +1407,8 @@ WARN_UNUSED_RESULT
 wasmCWriteMemoryGrow(
     const WasmCFunctionWriter* writer
 ) {
-    static const WasmOpcode opcode = wasmOpcodeMemoryGrow;
-
     WasmMemoryInstruction instruction;
-    if (!wasmMemoryInstructionRead(writer->code, opcode, &instruction)) {
+    if (!wasmMemoryInstructionRead(writer->code, &instruction)) {
         fprintf(stderr, "w2c2: invalid memory.grow instruction encoding\n");
         return false;
     }
@@ -1551,8 +1545,8 @@ wasmCWriteMemoryFill(
     const WasmCFunctionWriter* writer,
     const WasmMiscOpcode miscOpcode
 ) {
-    WasmMiscMemoryInstruction instruction;
-    if (!wasmMiscMemoryInstructionRead(writer->code, miscOpcode, &instruction)) {
+    WasmMemoryInstruction instruction;
+    if (!wasmMemoryInstructionRead(writer->code, &instruction)) {
         fprintf(stderr, "w2c2: invalid memory.fill instruction encoding\n");
         return false;
     }
@@ -2286,10 +2280,8 @@ WARN_UNUSED_RESULT
 wasmCWriteBranchExpr(
     const WasmCFunctionWriter* writer
 ) {
-    static const WasmOpcode opcode = wasmOpcodeBr;
-
     WasmBranchInstruction instruction;
-    if (!wasmBranchInstructionRead(writer->code, opcode, &instruction)) {
+    if (!wasmBranchInstructionRead(writer->code, &instruction)) {
         fprintf(stderr, "w2c2: invalid br instruction encoding\n");
         return false;
     }
@@ -2308,10 +2300,8 @@ WARN_UNUSED_RESULT
 wasmCWriteBranchIfExpr(
     WasmCFunctionWriter* writer
 ) {
-    static const WasmOpcode opcode = wasmOpcodeBrIf;
-
     WasmBranchInstruction instruction;
-    if (!wasmBranchInstructionRead(writer->code, opcode, &instruction)) {
+    if (!wasmBranchInstructionRead(writer->code, &instruction)) {
         fprintf(stderr, "w2c2: invalid br.if instruction encoding\n");
         return false;
     }
@@ -3614,7 +3604,7 @@ wasmCWriteConstantExpr(
         }
         case wasmOpcodeGlobalGet: {
             WasmGlobalInstruction instruction;
-            MUST (wasmGlobalInstructionRead(&code, opcode, &instruction))
+            MUST (wasmGlobalInstructionRead(&code, &instruction))
             MUST (wasmCWriteStringGlobalUse(builder, module, instruction.globalIndex, false))
             break;
         }
@@ -4860,19 +4850,19 @@ wasmCImplementationWriterThread(
         }
 
         {
-            WasmCImplementationWriterTask* task = writer->task;
+            const WasmCImplementationWriterTask* task = writer->task;
 
             const WasmModule* module = task->module;
             const char* moduleName = task->moduleName;
             const char* headerName = task->headerName;
-            char filePrefix = task->filePrefix;
-            U32 fileIndex = task->fileIndex;
-            U32 functionsPerFile = task->functionsPerFile;
-            U32 startFunctionIDIndex = task->startFunctionIDIndex;
-            WasmFunctionIDs functionIDs = task->functionIDs;
-            bool pretty = task->pretty;
-            bool debug = task->debug;
-            bool multipleModules = task->multipleModules;
+            const char filePrefix = task->filePrefix;
+            const U32 fileIndex = task->fileIndex;
+            const U32 functionsPerFile = task->functionsPerFile;
+            const U32 startFunctionIDIndex = task->startFunctionIDIndex;
+            const WasmFunctionIDs functionIDs = task->functionIDs;
+            const bool pretty = task->pretty;
+            const bool debug = task->debug;
+            const bool multipleModules = task->multipleModules;
             WasmDebugLines* debugLines = task->debugLines;
 
             writer->task = NULL;
@@ -4880,7 +4870,7 @@ wasmCImplementationWriterThread(
             pthread_mutex_unlock(&writer->mutex);
 
             {
-                bool result = wasmCWriteImplementationFile(
+                const bool result = wasmCWriteImplementationFile(
                     module,
                     moduleName,
                     headerName,
@@ -4895,7 +4885,7 @@ wasmCImplementationWriterThread(
                     multipleModules
                 );
                 if (!result) {
-                    WasmFunctionID startFunctionID = functionIDs.functionIDs[startFunctionIDIndex];
+                    const WasmFunctionID startFunctionID = functionIDs.functionIDs[startFunctionIDIndex];
                     fprintf(
                         stderr,
                         "w2c2: failed to write implementation file %d. start function index: %d\n",
diff --git a/w2c2/instruction.c b/w2c2/instruction.c
index b722800..cc32f9b 100644
--- a/w2c2/instruction.c
+++ b/w2c2/instruction.c
@@ -5,13 +5,11 @@
 bool
 wasmLocalInstructionRead(
     Buffer* buffer,
-    const WasmOpcode opcode,
     WasmLocalInstruction* result
 ) {
     U32 localIndex = 0;
     MUST (leb128ReadU32(buffer, &localIndex) > 0)
 
-    result->opcode = opcode;
     result->localIndex = localIndex;
 
     return true;
@@ -22,13 +20,11 @@ wasmLocalInstructionRead(
 bool
 wasmGlobalInstructionRead(
     Buffer* buffer,
-    const WasmOpcode opcode,
     WasmGlobalInstruction* result
 ) {
     U32 globalIndex = 0;
     MUST (leb128ReadU32(buffer, &globalIndex) > 0)
 
-    result->opcode = opcode;
     result->globalIndex = globalIndex;
 
     return true;
@@ -42,7 +38,6 @@ wasmConstInstructionRead(
     const WasmOpcode opcode,
     WasmConstInstruction* result
 ) {
-    result->opcode = opcode;
     switch (opcode) {
         case wasmOpcodeI32Const:
             return leb128ReadI32(buffer, &result->value.i32) > 0;
@@ -62,7 +57,6 @@ wasmConstInstructionRead(
 bool
 wasmLoadStoreInstructionRead(
     Buffer* buffer,
-    const WasmOpcode opcode,
     WasmLoadStoreInstruction* result
 ) {
     U32 align = 0;
@@ -71,7 +65,6 @@ wasmLoadStoreInstructionRead(
     MUST (leb128ReadU32(buffer, &align) > 0)
     MUST (leb128ReadU32(buffer, &offset) > 0)
 
-    result->opcode = opcode;
     result->align = align;
     result->offset = offset;
 
@@ -117,13 +110,11 @@ wasmCallIndirectInstructionRead(
 bool
 wasmBranchInstructionRead(
     Buffer* buffer,
-    const WasmOpcode opcode,
     WasmBranchInstruction* result
 ) {
     U32 labelIndex = 0;
     MUST(leb128ReadU32(buffer, &labelIndex) > 0)
 
-    result->opcode = opcode;
     result->labelIndex = labelIndex;
 
     return true;
@@ -171,31 +162,11 @@ wasmBranchTableInstructionFree(
 bool
 wasmMemoryInstructionRead(
     Buffer* buffer,
-    const WasmOpcode opcode,
     WasmMemoryInstruction* result
 ) {
     U32 memoryIndex = 0;
     MUST(leb128ReadU32(buffer, &memoryIndex) > 0)
 
-    result->opcode = opcode;
-    result->memoryIndex = memoryIndex;
-
-    return true;
-}
-
-/* WasmMiscMemoryInstruction */
-
-bool
-WARN_UNUSED_RESULT
-wasmMiscMemoryInstructionRead(
-    Buffer* buffer,
-    const WasmMiscOpcode opcode,
-    WasmMiscMemoryInstruction* result
-) {
-    U32 memoryIndex = 0;
-    MUST(leb128ReadU32(buffer, &memoryIndex) > 0)
-
-    result->opcode = opcode;
     result->memoryIndex = memoryIndex;
 
     return true;
@@ -219,4 +190,3 @@ wasmMemoryCopyInstructionRead(
 
     return true;
 }
-
diff --git a/w2c2/instruction.h b/w2c2/instruction.h
index bba6b68..2d33ea6 100644
--- a/w2c2/instruction.h
+++ b/w2c2/instruction.h
@@ -8,7 +8,6 @@
 /* WasmLocalInstruction */
 
 typedef struct WasmLocalInstruction {
-    WasmOpcode opcode;
     U32 localIndex;
 } WasmLocalInstruction;
 
@@ -16,14 +15,12 @@ bool
 WARN_UNUSED_RESULT
 wasmLocalInstructionRead(
     Buffer* buffer,
-    WasmOpcode opcode,
     WasmLocalInstruction* result
 );
 
 /* WasmGlobalInstruction */
 
 typedef struct WasmGlobalInstruction {
-    WasmOpcode opcode;
     U32 globalIndex;
 } WasmGlobalInstruction;
 
@@ -31,7 +28,6 @@ bool
 WARN_UNUSED_RESULT
 wasmGlobalInstructionRead(
     Buffer* buffer,
-    WasmOpcode opcode,
     WasmGlobalInstruction* result
 );
 
@@ -45,7 +41,6 @@ typedef union WasmValue {
 } WasmValue;
 
 typedef struct WasmConstInstruction {
-    WasmOpcode opcode;
     WasmValue value;
 } WasmConstInstruction;
 
@@ -60,7 +55,6 @@ wasmConstInstructionRead(
 /* WasmLoadStoreInstruction */
 
 typedef struct WasmLoadStoreInstruction {
-    WasmOpcode opcode;
     U32 align;
     U32 offset;
 } WasmLoadStoreInstruction;
@@ -69,7 +63,6 @@ bool
 WARN_UNUSED_RESULT
 wasmLoadStoreInstructionRead(
     Buffer* buffer,
-    WasmOpcode opcode,
     WasmLoadStoreInstruction* result
 );
 
@@ -103,7 +96,6 @@ wasmCallIndirectInstructionRead(
 /* WasmBranchInstruction */
 
 typedef struct WasmBranchInstruction {
-    WasmOpcode opcode;
     U32 labelIndex;
 } WasmBranchInstruction;
 
@@ -111,7 +103,6 @@ bool
 WARN_UNUSED_RESULT
 wasmBranchInstructionRead(
     Buffer* buffer,
-    WasmOpcode opcode,
     WasmBranchInstruction* result
 );
 
@@ -138,7 +129,6 @@ wasmBranchTableInstructionRead(
 /* WasmMemoryInstruction */
 
 typedef struct WasmMemoryInstruction {
-    WasmOpcode opcode;
     U32 memoryIndex;
 } WasmMemoryInstruction;
 
@@ -146,25 +136,9 @@ bool
 WARN_UNUSED_RESULT
 wasmMemoryInstructionRead(
     Buffer* buffer,
-    WasmOpcode opcode,
     WasmMemoryInstruction* result
 );
 
-/* WasmMiscMemoryInstruction */
-
-typedef struct WasmMiscMemoryInstruction {
-    WasmMiscOpcode opcode;
-    U32 memoryIndex;
-} WasmMiscMemoryInstruction;
-
-bool
-WARN_UNUSED_RESULT
-wasmMiscMemoryInstructionRead(
-    Buffer* buffer,
-    WasmMiscOpcode opcode,
-    WasmMiscMemoryInstruction* result
-);
-
 /* WasmMemoryCopyInstruction */
 
 typedef struct WasmMemoryCopyInstruction {
diff --git a/w2c2/main.c b/w2c2/main.c
index d573ad3..6a2609f 100644
--- a/w2c2/main.c
+++ b/w2c2/main.c
@@ -203,7 +203,7 @@ cleanImplementationFiles(void) {
 #if HAS_GLOB
     glob_t globbuf;
     size_t pathIndex = 0;
-    int globResult = glob("*.c", GLOB_NOSORT, NULL, &globbuf);
+    const int globResult = glob("*.c", GLOB_NOSORT, NULL, &globbuf);
     if (globResult != 0) {
         if (globResult != GLOB_NOMATCH) {
             fprintf(stderr, "w2c2: failed to glob files to clean\n");
diff --git a/w2c2/reader.c b/w2c2/reader.c
index 294a541..2610d8b 100644
--- a/w2c2/reader.c
+++ b/w2c2/reader.c
@@ -1088,7 +1088,7 @@ wasmReadConstantExpr(
         }
         case wasmOpcodeGlobalGet: {
             WasmGlobalInstruction instruction;
-            MUST (wasmGlobalInstructionRead(buffer, opcode, &instruction))
+            MUST (wasmGlobalInstructionRead(buffer, &instruction))
             break;
         }
         case wasmOpcodeEnd: