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backend-6502.c
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backend-6502.c
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/*
* 6502 backend for the Fuzix C Compiler
*
* The big challenge here is that the C stack is a software
* construct and so quite slow to adjust. As the compiler thinks
* mostly in terms of call frames we can avoid a chunk of the cost
* but not all of it.
*
* We try and reduce the cost by
* 1. Generating direct references whenever we can
* 2. When we need a helper and we can directly access we stuff the
* one side of the operation into @tmp
* 3. For certain operations we generate the left/right ourselves and
* go via the CPU stack. This is a win in some common cases like
* assignment, particularly on the 65C02
*
* For the rest we have to go via the C stack which whilst painfulf in
* places is helped by the relatively low clocks per instruction.
*
* Elements of this design like the separate stack with ZP pointer are
* heavily influenced by CC65 and one goal is to use many of the same
* support functions. Our pproach to code generation is however quite
* different and constrained by wanting to run on an 8bit micro.
*/
#include <stdio.h>
#include <stdint.h>
#include <stdlib.h>
#include <string.h>
#include <stdarg.h>
#include "compiler.h"
#include "backend.h"
#define NMOS_6502 0
#define CMOS_6502 1
#define BYTE(x) (((unsigned)(x)) & 0xFF)
#define WORD(x) (((unsigned)(x)) & 0xFFFF)
/*
* State for the current function
*/
static unsigned frame_len; /* Number of bytes of stack frame */
static unsigned sp; /* Stack pointer offset tracking */
static unsigned unreachable; /* Code following an unconditional jump */
static unsigned xlabel; /* Internal backend generated branches */
static unsigned argbase; /* Track shift between arguments and stack */
/*
* Node types we create in rewriting rules
*/
#define T_NREF (T_USER) /* Load of C global/static */
#define T_CALLNAME (T_USER+1) /* Function call by name */
#define T_NSTORE (T_USER+2) /* Store to a C global/static */
#define T_LREF (T_USER+3) /* Ditto for local */
#define T_LSTORE (T_USER+4)
#define T_LBREF (T_USER+5) /* Ditto for labelled strings or local static */
#define T_LBSTORE (T_USER+6)
#define T_RREF (T_USER+7)
#define T_RSTORE (T_USER+8)
#define T_RDEREF (T_USER+9) /* *regptr */
#define T_REQ (T_USER+10) /* *regptr */
/*
* 6502 specifics. We need to track some register values to produce
* bearable code
*/
static void output(const char *p, ...)
{
va_list v;
va_start(v, p);
putchar('\t');
vprintf(p, v);
putchar('\n');
va_end(v);
}
static void label(const char *p, ...)
{
va_list v;
va_start(v, p);
vprintf(p, v);
putchar(':');
putchar('\n');
va_end(v);
}
#define R_A 0
#define R_X 1
#define R_Y 2
#define INVALID 0
struct regtrack {
unsigned state;
uint8_t value;
unsigned snum;
unsigned offset;
};
struct regtrack reg[3];
static void invalidate_regs(void)
{
reg[R_A].state = INVALID;
reg[R_X].state = INVALID;
reg[R_Y].state = INVALID;
printf(";invalregs\n");
}
static void invalidate_a(void)
{
reg[R_A].state = INVALID;
}
static void invalidate_x(void)
{
reg[R_X].state = INVALID;
}
static void invalidate_y(void)
{
reg[R_Y].state = INVALID;
}
static void const_a_set(unsigned val)
{
if (reg[R_A].state == T_CONSTANT)
reg[R_A].value = val;
else
reg[R_A].state = INVALID;
}
static void const_x_set(unsigned val)
{
if (reg[R_X].state == T_CONSTANT)
reg[R_X].value = val;
else
reg[R_X].state = INVALID;
}
static void const_y_set(unsigned val)
{
if (reg[R_Y].state == T_CONSTANT)
reg[R_Y].value = val;
else
reg[R_Y].state = INVALID;
}
/* Get a value into A, adjust and track */
static void load_a(uint8_t n)
{
if (reg[R_A].state == T_CONSTANT) {
if (reg[R_A].value == n)
return;
}
/* No inca deca */
if (reg[R_X].state == T_CONSTANT && reg[R_X].value == n)
output("txa");
else if (reg[R_Y].state == T_CONSTANT && reg[R_Y].value == n)
output("tya");
else
output("lda #%u", n);
reg[R_A].state = T_CONSTANT;
reg[R_A].value = n;
}
/* Get a value into X, adjust and track */
static void load_x(uint8_t n)
{
if (reg[R_X].state == T_CONSTANT) {
if (reg[R_X].value == n)
return;
if (reg[R_X].value == n - 1) {
output("inx");
reg[R_X].value++;
return;
}
if (reg[R_X].value == n + 1) {
output("dex");
reg[R_X].value--;
return;
}
}
/* TODO: tyx for later CPU ? */
if (reg[R_A].state == T_CONSTANT && reg[R_A].value == n)
output("tax");
else
output("ldx #%u", n);
reg[R_X].state = T_CONSTANT;
reg[R_X].value = n;
}
/* Get a value into Y, adjust and track */
static void load_y(uint8_t n)
{
if (reg[R_Y].state == T_CONSTANT) {
if (reg[R_Y].value == n)
return;
if (reg[R_Y].value == n - 1) {
output("iny");
reg[R_Y].value++;
return;
}
if (reg[R_Y].value == n + 1) {
output("dey");
reg[R_Y].value--;
return;
}
}
/* TODO: tyx for later CPU ? */
if (reg[R_A].state == T_CONSTANT && reg[R_A].value == n)
output("tay");
else
output("ldy #%u", n);
reg[R_Y].state = T_CONSTANT;
reg[R_Y].value = n;
}
/*
* For now just try and eliminate the reloads. We shuld be able to
* eliminate some surplus stores with thought if we are careful
* how we defer them.
*/
static void set_xa_node(struct node *n)
{
unsigned op = n->op;
unsigned value = n->value;
/* Turn store forms into ref forms */
switch(op) {
case T_NSTORE:
op = T_NREF;
break;
case T_LBSTORE:
op = T_LBREF;
break;
case T_LSTORE:
op = T_LREF;
break;
case T_NAME:
case T_CONSTANT:
case T_NREF:
case T_LBREF:
case T_LREF:
case T_LOCAL:
case T_ARGUMENT:
break;
default:
invalidate_a();
invalidate_x();
printf("; invalidate xa\n");
return;
}
; printf("; set XA %x, %d\n", op, value);
reg[R_X].state = op;
reg[R_A].state = op;
reg[R_A].value = value;
reg[R_X].value = value;
reg[R_A].snum = n->snum;
reg[R_X].snum = n->snum;
return;
}
/* Can't deal with NREF until we propagate volatile info better */
static unsigned xa_contains(struct node *n)
{
// printf(";xa contains? %x %ld\n", n->op, n->value);
if (n->op == T_NREF)
return 0;
if (reg[R_A].state != n->op || reg[R_X].state != n->op)
return 0;
if (reg[R_A].value != n->value || reg[R_X].value != n->value)
return 0;
if (reg[R_A].snum != n->snum || reg[R_X].snum != n->snum)
return 0;
/* Looks good */
return 1;
}
static void set_a_node(struct node *n)
{
unsigned op = n->op;
unsigned value = n->value;
switch(op) {
case T_NAME:
case T_CONSTANT:
case T_NREF:
case T_NSTORE:
case T_LBREF:
case T_LBSTORE:
case T_LREF:
case T_LSTORE:
case T_LOCAL:
case T_ARGUMENT:
reg[R_A].state = op;
reg[R_A].value = value;
reg[R_A].snum = n->snum;
return;
default:
invalidate_a();
}
}
static unsigned a_contains(struct node *n)
{
if (reg[R_A].state != n->op)
return 0;
if (reg[R_A].value != n->value)
return 0;
if (reg[R_A].snum != n->snum)
return 0;
/* Looks good */
return 1;
}
/* Memory writes occured, invalidate according to what we know. Passing
NULL indicates unknown memory changes */
static void invalidate_node(struct node *n)
{
/* For now don't deal with the complex cases of whether we might
invalidate another object */
if (reg[R_A].state != T_CONSTANT)
reg[R_A].state = INVALID;
if (reg[R_X].state != T_CONSTANT)
reg[R_X].state = INVALID;
}
static void invalidate_mem(void)
{
if (reg[R_A].state != T_CONSTANT)
reg[R_A].state = INVALID;
if (reg[R_X].state != T_CONSTANT)
reg[R_X].state = INVALID;
}
static void set_reg(unsigned r, unsigned v)
{
reg[r].state = T_CONSTANT;
reg[r].value = (uint8_t)v;
}
/*
* Example size handling. In this case for a system that always
* pushes words.
*/
static unsigned get_size(unsigned t)
{
if (PTR(t))
return 2;
if (t == CSHORT || t == USHORT)
return 2;
if (t == CCHAR || t == UCHAR)
return 1;
if (t == CLONG || t == ULONG || t == FLOAT)
return 4;
if (t == CLONGLONG || t == ULONGLONG || t == DOUBLE)
return 8;
if (t == VOID)
return 0;
error("gs");
return 0;
}
/*
* For 6502 we keep byte objects byte size
*/
static unsigned get_stack_size(unsigned t)
{
return get_size(t);
}
/* Generate a call to an internal helper */
static void gen_internal(const char *p)
{
invalidate_regs();
output("jsr __%s", p);
}
/* Construct a direct operation if possible for the primary op */
static int do_pri8(struct node *n, const char *op, void (*pre)(struct node *__n))
{
struct node *r = n->right;
const char *name;
switch(n->op) {
case T_LABEL:
pre(n);
output("%s #<T%d+%d", op, n->val2, (unsigned)n->value);
return 1;
case T_NAME:
pre(n);
name = namestr(n->snum);
output("%s #<_%s+%d", op, name, (unsigned)n->value);
return 1;
case T_CONSTANT:
/* These had the right squashed into them */
case T_LREF:
case T_NREF:
case T_LBREF:
case T_LSTORE:
case T_NSTORE:
case T_LBSTORE:
/* These had the right squashed into them */
r = n;
break;
}
switch(r->op) {
case T_CONSTANT:
pre(n);
output("%s #%d", op, r->value & 0xFF);
return 1;
case T_LREF:
case T_LSTORE:
/* 255 is a fringe case we can do for 8bit but not split
8 and 16, so for now just skip it */
if (r->value < 254) {
pre(n);
load_y(r->value);
output("%s (@sp),y", op);
return 1;
}
/* For now punt */
return 0;
case T_NREF:
case T_NSTORE:
pre(n);
name = namestr(r->snum);
output("%s _%s+%d", op, name, (unsigned)r->value);
return 1;
case T_LBSTORE:
case T_LBREF:
pre(n);
output("%s T%d+%d", op, r->val2, (unsigned)r->value);
return 1;
/* If we add registers
case T_RREF:
output("%s __reg%d", op, r->val2);
return 1;*/
}
return 0;
}
/* Construct a direct operation if possible for the primary op */
static int do_pri8hi(struct node *n, const char *op, void (*pre)(struct node *__n))
{
struct node *r = n->right;
const char *name;
switch(n->op) {
case T_LABEL:
pre(n);
output("%s #>T%d+%d", op, n->val2, (unsigned)n->value);
return 1;
case T_NAME:
pre(n);
name = namestr(n->snum);
output("%s #_%s+%d", op, name, (unsigned)n->value);
return 1;
case T_CONSTANT:
/* These had the right squashed into them */
case T_LREF:
case T_NREF:
case T_LBREF:
case T_LSTORE:
case T_NSTORE:
case T_LBSTORE:
/* These had the right squashed into them */
r = n;
break;
}
switch(r->op) {
case T_CONSTANT:
pre(n);
output("%s #%d", op, (unsigned)(r->value >> 8));
return 1;
case T_LREF:
case T_LSTORE:
if (r->value < 254) {
pre(n);
load_y(r->value + 1) ;
output("%s (@sp),y", op);
return 1;
}
/* For now punt */
return 0;
case T_NREF:
case T_NSTORE:
pre(n);
name = namestr(r->snum);
output("%s _%s+%d", op, name, (unsigned)r->value + 1);
return 1;
case T_LBSTORE:
case T_LBREF:
pre(n);
output("%s T%d+%d", op, r->val2, (unsigned)r->value + 1);
return 1;
/* If we add registers
case T_RREF:
output("%s __reg%d+1", op, r->val2);
return 1;*/
}
return 0;
}
/* 16bit/ We are rather limited here because we only have a few ops with x */
static int do_pri16(struct node *n, const char *op, void (*pre)(struct node *__n))
{
struct node *r = n->right;
const char *name;
switch(n->op) {
case T_LABEL:
pre(n);
output("%sa #<T%d+%d", op, n->val2, (unsigned)n->value);
output("%sx #>T%d+%d", op, n->val2, ((unsigned)n->value) >> 8);
return 1;
case T_NAME:
pre(n);
name = namestr(n->snum);
output("%sa #<_%s+%d", op, n, (unsigned)n->value);
output("%sx #>_%s+%d", op, n, ((unsigned)n->value) >> 8);
return 1;
case T_LREF:
case T_NREF:
case T_LBREF:
case T_LSTORE:
case T_NSTORE:
case T_LBSTORE:
case T_CONSTANT:
/* These had the right squashed into them */
r = n;
}
switch(r->op) {
case T_CONSTANT:
pre(n);
output("%sa #%d", op, r->value & 0xFF);
output("%sx #%d", op, r->value >> 8);
return 1;
case T_LSTORE:
case T_LREF:
if (r->value < 255) {
pre(n);
load_y(r->value + 1);
output("%sa (@sp),y", op);
output("tax");
load_y(r->value);
output("%sa (@sp),y", op);
return 1;
}
/* For now punt */
return 0;
case T_NSTORE:
case T_NREF:
name = namestr(r->snum);
pre(n);
output("%sa _%s+%d", op, name, (unsigned)r->value);
output("%sx _%s+%d", op, name, ((unsigned)r->value) + 1);
return 1;
case T_LBSTORE:
case T_LBREF:
pre(n);
output("%sa T%d+%d", op, r->val2, (unsigned)r->value);
output("%sx T%d+%d", op, r->val2, ((unsigned)r->value) + 1);
return 1;
/* If we add registers
case T_RREF:
pre(n);
output("%sa __reg%dd", op, r->val2);
output("%sx __reg%d + 1", op, r->val2);
return 1;*/
}
return 0;
}
static void pre_none(struct node *n)
{
}
static void pre_store8(struct node *n)
{
output("sta @tmp");
}
static void pre_store16(struct node *n)
{
output("sta @tmp");
output("stx @tmp+1");
}
static int pri8(struct node *n, const char *op)
{
return do_pri8(n, op, pre_none);
}
static int pri16(struct node *n, const char *op)
{
return do_pri16(n, op, pre_none);
}
static int pri8_help(struct node *n, char *helper)
{
if (do_pri8(n, "lda", pre_store8)) {
/* Helper invalidates A itself */
helper_s(n, helper);
set_reg(R_Y, 0);
return 1;
}
return 0;
}
static int pri16_help(struct node *n, char *helper)
{
if (do_pri16(n, "ld", pre_store16)) {
/* Helper invalidates XA itself */
helper_s(n, helper);
set_reg(R_Y, 1);
return 1;
}
return 0;
}
static int pri_help(struct node *n, char *helper)
{
unsigned s = get_size(n->type);
if (s == 1 && pri8_help(n, helper))
return 1;
else if (s == 2 && pri16_help(n, helper))
return 1;
return 0;
}
static void pre_clc(struct node *n)
{
output("clc");
}
static void pre_sec(struct node *n)
{
output("sec");
}
static void pre_stash(struct node *n)
{
output("sta @tmp");
output("stx @tmp+1");
}
/*
* inc and dec are complicated but worth some effort as they
* are so commonly used for small constants. We could o with
* spotting and folding some stuff like *x++ perhaps to get a
* bit better codegen.
*/
/* Try to write inline inc and dec for simple forms */
/* TODO: sort out flag tests for dec */
static int leftop_memc(struct node *n, const char *op)
{
struct node *l = n->left;
struct node *r = n->right;
unsigned v;
unsigned sz = get_size(n->type);
char *name;
unsigned count;
unsigned nr = n->flags & NORETURN;
if (sz > 2)
return 0;
if (r->op != T_CONSTANT || r->value > 2)
return 0;
else
count = r->value;
/* Being super clever doesn't help if we need the value anyway */
if (!nr && (n->op == T_PLUSPLUS || n->op == T_MINUSMINUS))
return 0;
v = l->value;
switch(l->op) {
case T_NAME:
name = namestr(l->snum);
while(count--) {
output("%s _%s+%d", op, name, v);
if (sz == 2) {
output("beq X%d", ++xlabel);
output("%s _%s+%d", op, name, v + 1);
label("X%d", xlabel);
}
}
if (!nr) {
output("lda _%s+%d", name, v);
if (sz == 2)
output("ldx _%s+%d", name, v + 1);
}
return 1;
case T_LABEL:
while(count--) {
output("%s T%d+%d", op, (unsigned)l->val2, v);
if (sz == 2) {
output("beq X%d", ++xlabel);
output("%s T%d+%d", op, (unsigned)l->val2, v + 1);
label("X%d", xlabel);
}
}
if (nr == 1) {
output("lda T%d+%d", (unsigned)l->val2, v);
if (sz == 2)
output("ldx T%d+%d", (unsigned)l->val2, v + 1);
}
return 1;
case T_ARGUMENT:
v += argbase + frame_len;
case T_LOCAL:
return 0;
/* Don't seem to have a suitable addressing mode */
}
return 0;
}
/* Do a 16bit operation upper half by switching X into A */
static unsigned try_via_x(struct node *n, const char *op, void (*pre)(struct node *))
{
if (optsize) {
struct node *r = n->right;
unsigned rop = r->op;
if (rop == T_LREF) {
if (r->value == 0) {
output("jsr __%ssp0", op);
set_reg(R_Y, 1);
invalidate_x();
invalidate_a();
return 1;
} else if (r->value < 255) {
output("ldy #%d", r->value);
output("jsr __%spy", op);
const_y_set(reg[R_Y].value + 1);
invalidate_x();
invalidate_a();
return 1;
}
}
if (rop == T_CONSTANT && r->value < 256) {
load_y(r->value);
output("jsr __%s8y", op);
invalidate_x();
invalidate_a();
return 1;
}
}
/* Name and lbref are progably not worth it as have to go via tmp */
if (do_pri8(n, op, pre) == 0)
return 0;
output("pha");
output("txa");
memcpy(®[R_A], ®[R_X], sizeof(struct regtrack));
do_pri8hi(n, op, pre_none);
output("tax");
output("pla");
invalidate_a();
invalidate_x();
}
static void squash_node(struct node *n, struct node *o)
{
n->value = o->value;
n->val2 = o->val2;
n->snum = o->snum;
free_node(o);
}
static void squash_left(struct node *n, unsigned op)
{
struct node *l = n->left;
n->op = op;
squash_node(n, l);
n->left = NULL;
}
static void squash_right(struct node *n, unsigned op)
{
struct node *r = n->right;
n->op = op;
squash_node(n, r);
n->right = NULL;
}
static unsigned is_simple(struct node *n)
{
unsigned op = n->op;
/* Multi-word objects are never simple */
if (!PTR(n->type) && (n->type & ~UNSIGNED) > CSHORT)
return 0;
/* We can use these directly with primary operators on A */
if (op == T_CONSTANT || op == T_LABEL || op == T_NAME || (op == T_LREF && n->value < 255))
return 10;
/* Can go via @tmp */
if (op == T_NREF || op == T_LBREF)
return 1;
/* Hard */
return 0;
}
/* Chance to rewrite the tree from the top rather than none by node
upwards. We will use this for 8bit ops at some point and for cconly
propagation */
struct node *gen_rewrite(struct node *n)
{
return n;
}
/*
* Our chance to do tree rewriting. We don't do much for the 8080
* at this point, but we do rewrite name references and function calls
* to make them easier to process.
*
* We need to look at rewriting deref and assign with plus offset
* as if we've stuffed the ptr into tmp we can use ,y for deref
*/
struct node *gen_rewrite_node(struct node *n)
{
struct node *l = n->left;
struct node *r = n->right;
unsigned op = n->op;
unsigned nt = n->type;
/* TODO
- rewrite some reg ops
*/
/* *regptr */
if (op == T_DEREF && r->op == T_RREF) {
n->op = T_RDEREF;
n->right = NULL;
return n;
}
/* *regptr = */
if (op == T_EQ && l->op == T_RREF) {
n->op = T_REQ;
n->left = NULL;
return n;
}
/* Rewrite references into a load operation */
if (nt == CCHAR || nt == UCHAR || nt == CSHORT || nt == USHORT || PTR(nt)) {
if (op == T_DEREF) {
if (r->op == T_LOCAL || r->op == T_ARGUMENT) {
if (r->op == T_ARGUMENT)
r->value += argbase + frame_len;
squash_right(n, T_LREF);
return n;
}
if (r->op == T_REG) {
squash_right(n, T_RREF);
return n;
}
if (r->op == T_NAME) {
squash_right(n, T_NREF);
return n;
}
if (r->op == T_LABEL) {
squash_right(n, T_LBREF);
return n;
}
}
if (op == T_EQ) {
if (l->op == T_NAME) {
squash_left(n, T_NSTORE);
return n;
}
if (l->op == T_LABEL) {
squash_left(n, T_LBSTORE);
return n;
}
if (l->op == T_LOCAL || l->op == T_ARGUMENT) {
if (l->op == T_ARGUMENT)
l->value += argbase + frame_len;
squash_left(n, T_LSTORE);
return n;
}
if (l->op == T_REG) {
squash_left(n, T_RSTORE);
return n;
}
}
}
/* Eliminate casts for sign, pointer conversion or same */
if (op == T_CAST) {
if (nt == r->type || (nt ^ r->type) == UNSIGNED ||
(PTR(nt) && PTR(r->type))) {
free_node(n);
return r;
}
}
/* Rewrite function call of a name into a new node so we can
turn it easily into call xyz */
if (op == T_FUNCCALL && r->op == T_NAME && PTR(r->type) == 1) {
n->op = T_CALLNAME;
n->snum = r->snum;
n->value = r->value;
n->val2 = r->val2;
free_node(r);
n->right = NULL;
}
/* Commutive operations. We can swap the sides over on these */
if (op == T_AND || op == T_OR || op == T_HAT || op == T_STAR || op == T_PLUS) {
/* printf(";left %d right %d\n", is_simple(n->left), is_simple(n->right)); */
if (is_simple(n->left) > is_simple(n->right)) {
n->right = l;
n->left = r;
}
}
return n;
}
/* Export the C symbol */
void gen_export(const char *name)
{
output(".export _%s\n", name);
}
void gen_segment(unsigned s)
{
switch(s) {
case A_CODE:
output(".code");
break;
case A_DATA:
output(".data");
break;
case A_LITERAL:
output(".literal");
break;
case A_BSS:
output(".bss");
break;
default:
error("gseg");
}
}
void gen_prologue(const char *name)
{
printf("_%s:\n", name);
invalidate_regs();
}
/* Generate the stack frame */
void gen_frame(unsigned size, unsigned aframe)
{
frame_len = size;
if (size == 0)
return;
sp += size;
/* Maybe shortcut some common values ? */
if (size < 256) {
load_a(size);
gen_internal("enter8");
return;
}
load_a(size & 0xFF);
load_y(size >> 8);
gen_internal("enter16");
}
void gen_epilogue(unsigned size, unsigned argsize)
{
if (sp != size) {
error("sp");
}
sp -= size;
/* TODO arg removal */
if (size > 256) {
/* Ugly as we need to preserve AX */
output("pha");
load_a(size & 0xFF);
load_y(size >> 8);
gen_internal("return16");
output("pla");
}
else if (size) {
load_y(size);
gen_internal("return8");
}
else