cgen: skip empty asm amd64 {} blocks, to ease prototyping

Author: spytheman

vlib/v/gen/c/cgen.v

@@ -3337,6 +3337,10 @@ fn (mut g Gen) gen_attrs(attrs []ast.Attr) {
 }
 
 fn (mut g Gen) asm_stmt(stmt ast.AsmStmt) {
+	if stmt.templates.len == 0 && stmt.input.len == 0 && stmt.output.len == 0
+		&& stmt.global_labels.len == 0 && !stmt.is_goto && !stmt.is_volatile {
+		return
+	}
 	g.write('__asm__')
 	if stmt.is_volatile {
 		g.write(' volatile')

vlib/v/gen/c/text_manipulation.v

@@ -11,7 +11,7 @@ const trace_gen_wanted_value = $d('trace_gen_wanted_value', '')
 fn (mut g Gen) trace_gen_wanted_context(last_character_len int, s string) {
 	last_n := g.out.last_n(last_character_len)
 	eprintln('> trace_gen_wanted, last characters:\n${last_n}\n')
-	eprintln('> trace_gen_wanted, found wanted cgen string `${trace_gen_wanted_value}` in generated string ${s}')
+	eprintln("> trace_gen_wanted, found wanted cgen string `${trace_gen_wanted_value}` in generated string: \"${s}\"")
 	print_backtrace()
 }
 

vlib/v/slow_tests/assembly/asm_empty_statement_test.v

@@ -0,0 +1,7 @@
+fn test_empty_asm_statements() {
+	asm amd64 {
+	}
+	asm arm64 {
+	}
+	assert true
+}