From e754ca62dbe1826609a5a2623ec7d7df9dccac9b Mon Sep 17 00:00:00 2001
From: Evgeniy Stratonikov <evgeniy@nspcc.ru>
Date: Tue, 2 Mar 2021 14:34:23 +0300
Subject: [PATCH] compiler: do not emit CONVERT for syscall results

When we encounter type assertion CONVERT is emitted.
This isn't needed for SYSCALL (or opcode) results
because value already has needed type.
Problems can arise when result is converted to invalid type
but `neogointernal` package shouldn't be used directly anyway.
---
 pkg/compiler/codegen.go | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/pkg/compiler/codegen.go b/pkg/compiler/codegen.go
index 1baf52704..730256e9d 100644
--- a/pkg/compiler/codegen.go
+++ b/pkg/compiler/codegen.go
@@ -1226,6 +1226,10 @@ func (c *codegen) Visit(node ast.Node) ast.Visitor {
 	// not the assertion type.
 	case *ast.TypeAssertExpr:
 		ast.Walk(c, n.X)
+		if c.isCallExprSyscall(n.X) {
+			return nil
+		}
+
 		goTyp := c.typeOf(n.Type)
 		if canConvert(goTyp.String()) {
 			typ := toNeoType(goTyp)
@@ -1246,6 +1250,20 @@ func (c *codegen) packVarArgs(n *ast.CallExpr, typ *types.Signature) int {
 	return varSize
 }
 
+func (c *codegen) isCallExprSyscall(e ast.Expr) bool {
+	ce, ok := e.(*ast.CallExpr)
+	if !ok {
+		return false
+	}
+	sel, ok := ce.Fun.(*ast.SelectorExpr)
+	if !ok {
+		return false
+	}
+	name, _ := c.getFuncNameFromSelector(sel)
+	f, ok := c.funcs[name]
+	return ok && isSyscall(f)
+}
+
 // processDefers emits code for `defer` statements.
 // TRY-related opcodes handle exception as follows:
 // 1. CATCH block is executed only if exception has occurred.