[PATCH olang v1 0/1] deref operation returning value

[PATCH olang v1 0/1] deref operation returning value

[Carlos Maniero]

We had discussed over IRC about may adding some extra information on the
deref operation to support this feature, but there are two reasons why I
opted to keep this on code gen:

1) Modifying the AST would require changing the unary data structure
from a struct to an union, but no other operator would be beneficed by
this since only the deref needs some extra information.

2) The assign operation is required to identify if its LHS is a deref,
once the mov instruction will differ from a simple ref: The simple ref
will mov the expression result to a RBP offset and the deref will mov
the expression result to the pointer location.

Also, once we have the IR, this logic could easily fit the layer that
will build the IR.

Carlos Maniero (1):
  codegen: x64: deref returns pointer value

 src/codegen_x86_64.c | 61 +++++++++++++++++++++++++++++++++++++-------
 1 file changed, 52 insertions(+), 9 deletions(-)

-- 
2.46.1

[PATCH olang v1 1/1] codegen: x64: deref returns pointer value

[Carlos Maniero]

Deref is context dependent, when doing an assignment:

  *a = 1

It is expected for the deref codegen to return the pointer location, so
than the assignment binop would be able to assign a new value at that
location.

On another hand, when performing:

  return *a

It is expected for deref to actually returns the pointer location value.
The codegen of both behaviors were defined in new functions to avoid
indiscriminately increase the codegen_x86_64_emit_expression
switch/case.

Register choice:
================

Since the operation *mov (%rax), %rax* is not possible, I arbitrarily
choose R10 as it is a caller-saved register.

Signed-off-by: Carlos Maniero <carlos@maniero.me>
---
 src/codegen_x86_64.c | 61 +++++++++++++++++++++++++++++++++++++-------
 1 file changed, 52 insertions(+), 9 deletions(-)

diff --git a/src/codegen_x86_64.c b/src/codegen_x86_64.c
index deb7e24..db1b77a 100644
--- a/src/codegen_x86_64.c
+++ b/src/codegen_x86_64.c
@@ -52,6 +52,8 @@ typedef enum x86_64_register_type
     REG_R15
 } x86_64_register_type_t;
 
+typedef size_t size_in_bytes_t;
+
 /**
  * Arch/ABI      arg1  arg2  arg3  arg4  arg5  arg6  arg7  Notes
  * ──────────────────────────────────────────────────────────────
@@ -76,6 +78,14 @@ codegen_x86_64_put_stack_offset(codegen_x86_64_t *codegen,
 static size_t
 codegen_x86_64_get_stack_offset(codegen_x86_64_t *codegen, symbol_t *symbol);
 
+static size_in_bytes_t
+codegen_x86_64_emit_unary_deref_address(codegen_x86_64_t *codegen,
+                                              ast_unary_op_t *unary_op);
+
+static size_in_bytes_t
+codegen_x86_64_emit_unary_deref_value(codegen_x86_64_t *codegen,
+                                            ast_unary_op_t *unary_op);
+
 static size_t
 type_to_bytes(type_t *type);
 
@@ -126,8 +136,6 @@ codegen_x86_64_get_next_label(codegen_x86_64_t *codegen)
     return ++codegen->label_index;
 }
 
-typedef size_t size_in_bytes_t;
-
 static size_in_bytes_t
 codegen_x86_64_emit_expression(codegen_x86_64_t *codegen, ast_node_t *expr_node)
 {
@@ -619,7 +627,8 @@ codegen_x86_64_emit_expression(codegen_x86_64_t *codegen, ast_node_t *expr_node)
                                        AST_UNARY_DEREFERENCE &&
                                    "unsupported assignment lhs");
 
-                            codegen_x86_64_emit_expression(codegen, bin_op.lhs);
+                            codegen_x86_64_emit_unary_deref_address(
+                                codegen, &bin_op.lhs->as_unary_op);
 
                             fprintf(codegen->out, "    push %%rax\n");
 
@@ -679,12 +688,8 @@ codegen_x86_64_emit_expression(codegen_x86_64_t *codegen, ast_node_t *expr_node)
                     return 8;
                 }
                 case AST_UNARY_DEREFERENCE: {
-                    // FIXME: support dereference of dereference (**)
-                    assert(unary_op.expr->kind == AST_NODE_REF &&
-                           "unsupported unary expression for dereference (*)");
-
-                    return codegen_x86_64_emit_expression(codegen,
-                                                          unary_op.expr);
+                    return codegen_x86_64_emit_unary_deref_value(
+                        codegen, &unary_op);
                 }
                 default: {
                     assert(0 && "unsupported unary operation");
@@ -829,6 +834,44 @@ codegen_x86_64_emit_if(codegen_x86_64_t *codegen, ast_if_stmt_t if_stmt)
     fprintf(codegen->out, ".L%ld:\n", end_else_label);
 }
 
+static size_in_bytes_t
+codegen_x86_64_emit_unary_deref_address(codegen_x86_64_t *codegen,
+                                              ast_unary_op_t *unary_op)
+{
+    assert(unary_op->kind == AST_UNARY_DEREFERENCE);
+    // FIXME: support dereference of dereference (**)
+    assert(unary_op->expr->kind == AST_NODE_REF &&
+           "unsupported unary expression for dereference (*)");
+
+    return codegen_x86_64_emit_expression(codegen, unary_op->expr);
+}
+
+static size_in_bytes_t
+codegen_x86_64_emit_unary_deref_value(codegen_x86_64_t *codegen,
+                                            ast_unary_op_t *unary_op)
+{
+    codegen_x86_64_emit_unary_deref_address(codegen, unary_op);
+
+    ast_ref_t ref = unary_op->expr->as_ref;
+
+    symbol_t *symbol = scope_lookup(ref.scope, ref.id);
+
+    assert(symbol->type->kind == TYPE_PTR);
+
+    size_in_bytes_t deref_size = type_to_bytes(symbol->type->as_ptr.type);
+
+    fprintf(codegen->out,
+            "    mov (%%rax), %s\n",
+            get_reg_for(REG_R10, deref_size));
+
+    fprintf(codegen->out,
+            "    mov %s, %s\n",
+            get_reg_for(REG_R10, deref_size),
+            get_reg_for(REG_ACCUMULATOR, deref_size));
+
+    return deref_size;
+}
+
 static size_t
 type_to_bytes(type_t *type)
 {
-- 
2.46.1

[olang/patches/.build.yml] build failed

[builds.sr.ht]

olang/patches/.build.yml: FAILED in 20s

[deref operation returning value][0] from [Carlos Maniero][1]

[0]: https://lists.sr.ht/~johnnyrichard/olang-devel/patches/55515
[1]: mailto:carlos@maniero.me

✗ #1352279 FAILED olang/patches/.build.yml https://builds.sr.ht/~johnnyrichard/job/1352279

Re: [olang/patches/.build.yml] build failed

[Carlos Maniero]

I broke the format :(

I'll wait for the review before submitting a v2.