From 667769d1c0d963114ca9c026a7ed039734de10e2 Mon Sep 17 00:00:00 2001
From: Lorenzo Torres <lorenzo@sagittarius-a.org>
Date: Sat, 17 Jan 2026 10:33:19 +0100
Subject: [PATCH] implement array subscript for assignment in codegen

---
 codegen.c | 110 +++++++++++++++++++++++++++++++++++++++++++++++++++---
 test      | Bin 0 -> 20368 bytes
 test.s    |  90 ++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 195 insertions(+), 5 deletions(-)
 create mode 100755 test
 create mode 100644 test.s

diff --git a/codegen.c b/codegen.c
index 552bb77..d1c58fd 100644
--- a/codegen.c
+++ b/codegen.c
@@ -152,14 +152,114 @@ void gen_binary(FILE *fp, ast_node *expr)
 			fprintf(fp, "or %%rcx, %%rax\n");
 			break;
 		case OP_ASSIGN: {
-			if (expr->expr.binary.left->type != NODE_IDENTIFIER) {
+			if (expr->expr.binary.left->type == NODE_IDENTIFIER) {
+				gen_expr(fp, expr->expr.binary.right);
+				int offset = get_var_offset(expr->expr.binary.left->expr.string.start,
+				expr->expr.binary.left->expr.string.len);
+				fprintf(fp, "mov %%rax, -%d(%%rbp)\n", offset);
+			} else if (expr->expr.binary.left->type == NODE_ARRAY_SUBSCRIPT) {
+				ast_node *subscript = expr->expr.binary.left;
+				usize element_size = 8;
+				type *base_type = subscript->expr.subscript.expr->expr_type;
+				bool is_slice = false;
+
+				if (base_type) {
+					if (base_type->tag == TYPE_PTR && base_type->data.ptr.child) {
+						element_size = base_type->data.ptr.child->size;
+					} else if (base_type->tag == TYPE_SLICE && base_type->data.slice.child) {
+						element_size = base_type->data.slice.child->size;
+						is_slice = true;
+					}
+				}
+
+				if (subscript->expr.subscript.expr->type == NODE_IDENTIFIER && is_slice) {
+					int base_offset = get_var_offset(subscript->expr.subscript.expr->expr.string.start,
+					                                  subscript->expr.subscript.expr->expr.string.len);
+
+					fprintf(fp, "mov -%d(%%rbp), %%rcx\n", base_offset);
+					gen_expr(fp, subscript->expr.subscript.index);
+
+					if (element_size != 1) {
+						fprintf(fp, "imul $%lu, %%rax\n", element_size);
+					}
+
+					fprintf(fp, "add %%rcx, %%rax\n");
+					fprintf(fp, "push %%rax\n");
+
+					gen_expr(fp, expr->expr.binary.right);
+
+					fprintf(fp, "pop %%rcx\n");
+
+					if (subscript->expr_type && subscript->expr_type->size == 4) {
+						fprintf(fp, "mov %%eax, (%%rcx)\n");
+					} else if (subscript->expr_type && subscript->expr_type->size == 2) {
+						fprintf(fp, "mov %%ax, (%%rcx)\n");
+					} else if (subscript->expr_type && subscript->expr_type->size == 1) {
+						fprintf(fp, "mov %%al, (%%rcx)\n");
+					} else {
+						fprintf(fp, "mov %%rax, (%%rcx)\n");
+					}
+				} else if (subscript->expr.subscript.expr->type == NODE_IDENTIFIER) {
+					int base_offset = get_var_offset(subscript->expr.subscript.expr->expr.string.start,
+					                                  subscript->expr.subscript.expr->expr.string.len);
+
+					gen_expr(fp, subscript->expr.subscript.index);
+
+					if (element_size != 1) {
+						fprintf(fp, "imul $%lu, %%rax\n", element_size);
+					}
+
+					fprintf(fp, "add $%d, %%rax\n", base_offset);
+					fprintf(fp, "neg %%rax\n");
+					fprintf(fp, "add %%rbp, %%rax\n");
+					fprintf(fp, "push %%rax\n");
+
+					gen_expr(fp, expr->expr.binary.right);
+
+					fprintf(fp, "pop %%rcx\n");
+
+					if (subscript->expr_type && subscript->expr_type->size == 4) {
+						fprintf(fp, "mov %%eax, (%%rcx)\n");
+					} else if (subscript->expr_type && subscript->expr_type->size == 2) {
+						fprintf(fp, "mov %%ax, (%%rcx)\n");
+					} else if (subscript->expr_type && subscript->expr_type->size == 1) {
+						fprintf(fp, "mov %%al, (%%rcx)\n");
+					} else {
+						fprintf(fp, "mov %%rax, (%%rcx)\n");
+					}
+				} else {
+					gen_expr(fp, subscript->expr.subscript.expr);
+					fprintf(fp, "push %%rax\n");
+
+					gen_expr(fp, subscript->expr.subscript.index);
+
+					if (element_size != 1) {
+						fprintf(fp, "imul $%lu, %%rax\n", element_size);
+					}
+
+					fprintf(fp, "pop %%rcx\n");
+					fprintf(fp, "add %%rcx, %%rax\n");
+					fprintf(fp, "push %%rax\n");
+
+					gen_expr(fp, expr->expr.binary.right);
+
+					fprintf(fp, "pop %%rcx\n");
+
+					if (subscript->expr_type && subscript->expr_type->size == 4) {
+						fprintf(fp, "mov %%eax, (%%rcx)\n");
+					} else if (subscript->expr_type && subscript->expr_type->size == 2) {
+						fprintf(fp, "mov %%ax, (%%rcx)\n");
+					} else if (subscript->expr_type && subscript->expr_type->size == 1) {
+						fprintf(fp, "mov %%al, (%%rcx)\n");
+					} else {
+						fprintf(fp, "mov %%rax, (%%rcx)\n");
+					}
+				}
+			} else {
 				fprintf(fp, "# ERROR: left side of assignment must be identifier\n");
 				break;
 			}
-			gen_expr(fp, expr->expr.binary.right);
-			int offset = get_var_offset(expr->expr.binary.left->expr.string.start,
-			                            expr->expr.binary.left->expr.string.len);
-			fprintf(fp, "mov %%rax, -%d(%%rbp)\n", offset);
+			
 			break;
 		}
 		case OP_ASSIGN_PTR: {
diff --git a/test b/test
new file mode 100755
index 0000000000000000000000000000000000000000..1b89d353242a021ce1ef52d7b784b465683311ed
GIT binary patch
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diff --git a/test.s b/test.s
new file mode 100644
index 0000000..b86c66e
--- /dev/null
+++ b/test.s
@@ -0,0 +1,90 @@
+.section .text
+.global main
+main:
+push %rbp
+mov %rsp, %rbp
+sub $256, %rsp
+movb $72, -32(%rbp)
+movb $101, -31(%rbp)
+movb $108, -30(%rbp)
+movb $108, -29(%rbp)
+movb $111, -28(%rbp)
+movb $32, -27(%rbp)
+movb $119, -26(%rbp)
+movb $111, -25(%rbp)
+movb $114, -24(%rbp)
+movb $108, -23(%rbp)
+movb $100, -22(%rbp)
+movb $33, -21(%rbp)
+movb $10, -20(%rbp)
+lea -32(%rbp), %rax
+mov %rax, -48(%rbp)
+mov $14, %rax
+mov %rax, -40(%rbp)
+mov -40(%rbp), %rax
+push %rax
+pop %rdi
+call malloc
+mov %rax, -56(%rbp)
+mov -56(%rbp), %rcx
+mov $0, %rax
+push %rax
+mov $13, %rax
+mov %rax, %rdx
+pop %rax
+mov %rdx, %r8
+sub %rax, %r8
+inc %r8
+add %rcx, %rax
+mov %rax, -88(%rbp)
+mov %r8, -80(%rbp)
+lea -88(%rbp), %rax
+mov (%rax), %rcx
+mov 8(%rax), %rdx
+mov %rcx, -72(%rbp)
+mov %rdx, -64(%rbp)
+mov $0, %rax
+mov %rax, -96(%rbp)
+.L0:
+mov -96(%rbp), %rax
+mov %rax, %rcx
+mov -40(%rbp), %rax
+cmp %rax, %rcx
+setl %al
+movzx %al, %rax
+test %rax, %rax
+jz .L1
+mov -72(%rbp), %rcx
+mov -96(%rbp), %rax
+add %rcx, %rax
+push %rax
+mov -48(%rbp), %rcx
+mov -96(%rbp), %rax
+add %rcx, %rax
+movzbl (%rax), %eax
+pop %rcx
+mov %al, (%rcx)
+mov -96(%rbp), %rax
+mov %rax, %rcx
+mov $1, %rax
+add %rcx, %rax
+mov %rax, -96(%rbp)
+jmp .L0
+.L1:
+mov $1, %rax
+push %rax
+mov -72(%rbp), %rax
+push %rax
+mov -64(%rbp), %rax
+push %rax
+pop %rdx
+pop %rsi
+pop %rdi
+call write
+mov $0, %rax
+mov %rbp, %rsp
+pop %rbp
+ret
+mov %rbp, %rsp
+pop %rbp
+ret