core/vm: return copy of input slice in identity precompile, avoid ret…

…urndata copy (ethereum#25183)

* core/vm: return copy of input slice in identity precompile.  don't deep copy return data slice upon call completion

* make use of common.CopyBytes

core/vm/contracts.go

@@ -235,7 +235,7 @@ func (c *dataCopy) RequiredGas(input []byte) uint64 {
 	return uint64(len(input)+31)/32*params.IdentityPerWordGas + params.IdentityBaseGas
 }
 func (c *dataCopy) Run(in []byte) ([]byte, error) {
-	return in, nil
+	return common.CopyBytes(in), nil
 }
 
 // bigModExp implements a native big integer exponential modular operation.

core/vm/instructions.go

@@ -697,7 +697,6 @@ func opCall(pc *uint64, interpreter *EVMInterpreter, scope *ScopeContext) ([]byt
 	}
 	stack.push(&temp)
 	if err == nil || err == ErrExecutionReverted {
-		ret = common.CopyBytes(ret)
 		scope.Memory.Set(retOffset.Uint64(), retSize.Uint64(), ret)
 	}
 	scope.Contract.Gas += returnGas
@@ -733,7 +732,6 @@ func opCallCode(pc *uint64, interpreter *EVMInterpreter, scope *ScopeContext) ([
 	}
 	stack.push(&temp)
 	if err == nil || err == ErrExecutionReverted {
-		ret = common.CopyBytes(ret)
 		scope.Memory.Set(retOffset.Uint64(), retSize.Uint64(), ret)
 	}
 	scope.Contract.Gas += returnGas
@@ -762,7 +760,6 @@ func opDelegateCall(pc *uint64, interpreter *EVMInterpreter, scope *ScopeContext
 	}
 	stack.push(&temp)
 	if err == nil || err == ErrExecutionReverted {
-		ret = common.CopyBytes(ret)
 		scope.Memory.Set(retOffset.Uint64(), retSize.Uint64(), ret)
 	}
 	scope.Contract.Gas += returnGas
@@ -791,7 +788,6 @@ func opStaticCall(pc *uint64, interpreter *EVMInterpreter, scope *ScopeContext)
 	}
 	stack.push(&temp)
 	if err == nil || err == ErrExecutionReverted {
-		ret = common.CopyBytes(ret)
 		scope.Memory.Set(retOffset.Uint64(), retSize.Uint64(), ret)
 	}
 	scope.Contract.Gas += returnGas