From a9ace0cd8dbffb0a58f24c5b3e16dd658606dabd Mon Sep 17 00:00:00 2001
From: Alexander Medvednikov <alexander@medvednikov.com>
Date: Wed, 25 Mar 2026 16:42:21 +0300
Subject: [PATCH] cgen: fix asm volatile with no instructions generating
 invalid c code (fixes #26719)

---
 vlib/v/gen/c/cgen.v                           | 64 ++++++++++---------
 ..._empty_template_memory_barrier.c.must_have |  3 +
 .../asm_empty_template_memory_barrier.vv      |  5 ++
 3 files changed, 42 insertions(+), 30 deletions(-)
 create mode 100644 vlib/v/gen/c/testdata/asm_empty_template_memory_barrier.c.must_have
 create mode 100644 vlib/v/gen/c/testdata/asm_empty_template_memory_barrier.vv

diff --git a/vlib/v/gen/c/cgen.v b/vlib/v/gen/c/cgen.v
index d6d0cb151..f12d8fceb 100644
--- a/vlib/v/gen/c/cgen.v
+++ b/vlib/v/gen/c/cgen.v
@@ -4215,41 +4215,45 @@ fn (mut g Gen) asm_stmt(stmt ast.AsmStmt) {
 	}
 	g.writeln(' (')
 	g.indent++
-	for template_tmp in stmt.templates {
-		mut template := template_tmp
-		g.write('"')
-		if template.is_directive {
-			g.write('.')
-		}
-		g.write(template.name)
-		if template.is_label {
-			g.write(':')
-		} else {
-			g.write(' ')
-		}
-		// swap destination and operands for att syntax, not for arm64
-		if template.args.len != 0 && !template.is_directive
-			&& stmt.arch !in [.arm64, .s390x, .ppc64le, .loongarch64, .rv64, .rv32] {
-			template.args.prepend(template.args.last())
-			template.args.delete(template.args.len - 1)
-		}
-
-		for i, arg in template.args {
-			if stmt.arch == .amd64 && (template.name == 'call' || template.name[0] == `j`)
-				&& arg is ast.AsmRegister {
-				g.write('*') // indirect branching
+	if stmt.templates.len == 0 {
+		g.writeln('""')
+	} else {
+		for template_tmp in stmt.templates {
+			mut template := template_tmp
+			g.write('"')
+			if template.is_directive {
+				g.write('.')
+			}
+			g.write(template.name)
+			if template.is_label {
+				g.write(':')
+			} else {
+				g.write(' ')
+			}
+			// swap destination and operands for att syntax, not for arm64
+			if template.args.len != 0 && !template.is_directive
+				&& stmt.arch !in [.arm64, .s390x, .ppc64le, .loongarch64, .rv64, .rv32] {
+				template.args.prepend(template.args.last())
+				template.args.delete(template.args.len - 1)
 			}
 
-			g.asm_arg(arg, stmt)
-			if i + 1 < template.args.len {
-				g.write(', ')
+			for i, arg in template.args {
+				if stmt.arch == .amd64 && (template.name == 'call' || template.name[0] == `j`)
+					&& arg is ast.AsmRegister {
+					g.write('*') // indirect branching
+				}
+
+				g.asm_arg(arg, stmt)
+				if i + 1 < template.args.len {
+					g.write(', ')
+				}
 			}
-		}
 
-		if !template.is_label {
-			g.write('\\n\\t')
+			if !template.is_label {
+				g.write('\\n\\t')
+			}
+			g.writeln('"')
 		}
-		g.writeln('"')
 	}
 
 	if stmt.output.len != 0 || stmt.input.len != 0 || stmt.clobbered.len != 0 || stmt.is_goto {
diff --git a/vlib/v/gen/c/testdata/asm_empty_template_memory_barrier.c.must_have b/vlib/v/gen/c/testdata/asm_empty_template_memory_barrier.c.must_have
new file mode 100644
index 000000000..11616f6d3
--- /dev/null
+++ b/vlib/v/gen/c/testdata/asm_empty_template_memory_barrier.c.must_have
@@ -0,0 +1,3 @@
+__asm__ volatile (
+""
+: : : "memory"
diff --git a/vlib/v/gen/c/testdata/asm_empty_template_memory_barrier.vv b/vlib/v/gen/c/testdata/asm_empty_template_memory_barrier.vv
new file mode 100644
index 000000000..b42d9f73b
--- /dev/null
+++ b/vlib/v/gen/c/testdata/asm_empty_template_memory_barrier.vv
@@ -0,0 +1,5 @@
+fn main() {
+	asm volatile amd64 {
+		; ; ; memory
+	}
+}
-- 
2.39.5