examples: add a brainfuck->wasm compiler example (#19492)

examples/wasm_codegen/bf_compiler.v

@@ -0,0 +1,132 @@
+import os
+import wasm
+
+const runtime_page = 1024 * 64 // 64 KiBs
+
+fn generate_ciovec(mut start wasm.Function, sp wasm.LocalIndex) {
+	// construct struct __wasi_ciovec_t
+	//
+	// field, `const uint8_t *buf`
+	start.i32_const(runtime_page)
+	start.local_get(sp)
+	start.store(.i32_t, 2, 0)
+	// field, `__wasi_size_t buf_len`
+	start.i32_const(runtime_page)
+	start.i32_const(1) // len
+	start.store(.i32_t, 2, 4)
+}
+
+fn generate_code(mut start wasm.Function, bf_expr string) {
+	// locals are initialised to zero, by spec
+	sp := start.new_local_named(.i32_t, 'sp')
+
+	mut loop_labels := []wasm.LabelIndex{}
+	mut block_labels := []wasm.LabelIndex{}
+
+	// our page, the second one
+
+	for ch in bf_expr {
+		match ch {
+			`>` {
+				start.local_get(sp)
+				start.i32_const(1)
+				start.add(.i32_t)
+				start.local_set(sp)
+			}
+			`<` {
+				start.local_get(sp)
+				start.i32_const(1)
+				start.sub(.i32_t)
+				start.local_set(sp)
+			}
+			`+` {
+				start.local_get(sp)
+				{
+					start.local_get(sp)
+					start.load8(.i32_t, false, 0, 0)
+					start.i32_const(1)
+					start.add(.i32_t)
+				}
+				start.store8(.i32_t, 0, 0)
+			}
+			`-` {
+				start.local_get(sp)
+				{
+					start.local_get(sp)
+					start.load8(.i32_t, false, 0, 0)
+					start.i32_const(1)
+					start.sub(.i32_t)
+				}
+				start.store8(.i32_t, 0, 0)
+			}
+			`.` {
+				generate_ciovec(mut start, sp)
+
+				start.i32_const(1) // stdout
+				start.i32_const(runtime_page) // *iovs
+				start.i32_const(1) // iovs_len
+				start.i32_const(runtime_page + 1024) // *nwritten
+				start.call_import('wasi_unstable', 'fd_write')
+				start.drop() // ignore errno
+			}
+			`,` {
+				generate_ciovec(mut start, sp)
+
+				start.i32_const(0) // stdin
+				start.i32_const(runtime_page) // *iovs
+				start.i32_const(1) // iovs_len
+				start.i32_const(runtime_page + 1024) // *nwritten
+				start.call_import('wasi_unstable', 'fd_read')
+				start.drop() // ignore errno
+			}
+			`[` {
+				block_lbl := start.c_block([], [])
+				loop_lbl := start.c_loop([], [])
+				{
+					start.local_get(sp)
+					start.load8(.i32_t, false, 0, 0)
+					start.eqz(.i32_t)
+					start.c_br_if(block_lbl)
+				}
+				loop_labels << loop_lbl
+				block_labels << block_lbl
+			}
+			`]` {
+				loop_lbl := loop_labels.pop()
+				start.c_br(loop_lbl) // jump back to top
+				start.c_end(loop_lbl)
+				start.c_end(block_labels.pop())
+			}
+			else {}
+		}
+	}
+}
+
+@[noreturn]
+fn usage() {
+	eprintln('Usage: bf <expr> <outfile>')
+	exit(1)
+}
+
+fn main() {
+	bf_expr := os.args[1] or { usage() }
+
+	outfile := os.args[2] or { usage() }
+
+	mut m := wasm.Module{}
+	m.enable_debug('wasm bf')
+	m.new_function_import('wasi_unstable', 'fd_write', [.i32_t, .i32_t, .i32_t, .i32_t],
+		[.i32_t])
+	m.new_function_import('wasi_unstable', 'fd_read', [.i32_t, .i32_t, .i32_t, .i32_t],
+		[.i32_t])
+	m.assign_memory('memory', true, 2, none)
+
+	mut start := m.new_function('_start', [], [])
+	{
+		generate_code(mut start, bf_expr)
+	}
+	m.commit(start, true)
+
+	bytes := m.compile()
+	os.write_file_array(outfile, bytes)!
+}