backend-default.c

#include <stdio.h>
#include <stdint.h>
#include <stdlib.h>
#include "compiler.h"
#include "backend.h"

#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 */

/* 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
 *	at this point, but we do rewrite name references and function calls
 *	to make them easier to process.
 */
struct node *gen_rewrite_node(struct node *n)
{
	return n;
}

/* Export the C symbol */
void gen_export(const char *name)
{
	printf("	.export _%s\n", name);
}

void gen_segment(unsigned s)
{
	switch(s) {
	case A_CODE:
		printf("\t.code\n");
		break;
	case A_DATA:
		printf("\t.data\n");
		break;
	case A_LITERAL:
		printf("\t.literal\n");
		break;
	case A_BSS:
		printf("\t.bss\n");
		break;
	default:
		error("gseg");
	}
}

void gen_prologue(const char *name)
{
	printf("_%s:\n", name);
}

/* Generate the stack frame */
void gen_frame(unsigned size, unsigned aframe)
{
	frame_len = size;
	sp += size;
	gen_helpcall(NULL);
	printf("enter\n");
	gen_value(UINT, size);
}

void gen_epilogue(unsigned size, unsigned argsize)
{
	if (sp != size) {
		error("sp");
	}
	sp -= size;
	gen_helpcall(NULL);
	printf("exit\n");
	gen_value(UINT, size);
	printf("\tret\n");
}

void gen_label(const char *tail, unsigned n)
{
	printf("L%d%s:\n", n, tail);
}

unsigned gen_exit(const char *tail, unsigned n)
{
	printf("\tjmp L%d%s\n", n, tail);
	return 0;
}

void gen_jump(const char *tail, unsigned n)
{
	printf("\tjmp L%d%s\n", n, tail);
}

void gen_jfalse(const char *tail, unsigned n)
{
	printf("\tjz L%d%s\n", n, tail);
}

void gen_jtrue(const char *tail, unsigned n)
{
	printf("\tjnz L%d%s\n", n, tail);
}

void gen_switch(unsigned n, unsigned type)
{
	gen_helpcall(NULL);
	printf("switch");
	helper_type(type, 0);
	printf("\n\t.word Sw%d\n", n);
}

void gen_switchdata(unsigned n, unsigned size)
{
	printf("Sw%d:\n", n);
	printf("\t.word %d\n", size);
}

void gen_case_label(unsigned tag, unsigned entry)
{
	printf("Sw%d_%d:\n", tag, entry);
}

void gen_case_data(unsigned tag, unsigned entry)
{
	printf("\t.word Sw%d_%d\n", tag, entry);
}

void gen_helpcall(struct node *n)
{
	printf("\tcall __");
}

void gen_helptail(struct node *n)
{
}

void gen_helpclean(struct node *n)
{
}

void gen_data_label(const char *name, unsigned align)
{
	printf("_%s:\n", name);
}

void gen_space(unsigned value)
{
	printf("\t.ds %d\n", value);
}

void gen_text_data(struct node *n)
{
	printf("\t.word T%d\n", n->val2);
}

void gen_literal(unsigned n)
{
	if (n)
		printf("T%d:\n", n);
}

void gen_name(struct node *n)
{
	printf("\t.word _%s+%d\n", namestr(n->snum), WORD(n->value));
}

void gen_value(unsigned type, unsigned long value)
{
	if (PTR(type)) {
		printf("\t.word %u\n", (unsigned) value);
		return;
	}
	switch (type) {
	case CCHAR:
	case UCHAR:
		printf("\t.byte %u\n", (unsigned) value & 0xFF);
		break;
	case CSHORT:
	case USHORT:
		printf("\t.word %d\n", (unsigned) value & 0xFFFF);
		break;
	case CLONG:
	case ULONG:
	case FLOAT:
		/* We are little endian */
		printf("\t.word %d\n", (unsigned) (value & 0xFFFF));
		printf("\t.word %d\n", (unsigned) ((value >> 16) & 0xFFFF));
		break;
	default:
		error("unsuported type");
	}
}

void gen_start(void)
{
	printf("\t.code\n");
}

void gen_end(void)
{
}

void gen_tree(struct node *n)
{
	codegen_lr(n);
	printf(";\n");
}

/*
 *	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;
}

static unsigned get_stack_size(unsigned t)
{
	unsigned n = get_size(t);
	if (n == 1)
		return 2;
	return n;
}

unsigned gen_push(struct node *n)
{
	/* Our push will put the object on the stack, so account for it */
	sp += get_stack_size(n->type);
	return 0;
}

/*
 *	If possible turn this node into a direct access. We've already checked
 *	that the right hand side is suitable. If this returns 0 it will instead
 *	fall back to doing it stack based.
 */
unsigned gen_direct(struct node *n)
{
	switch(n->op) {
	/* Clean up is special and must be handled directly. It also has the
	   type of the function return so don't use that for the cleanup value
	   in n->right */
	case T_CLEANUP:
		gen_helpcall(NULL);
		printf("cleanup\n");
		gen_value(UINT, n->right->value);
		sp -= n->right->value;
		return 1;
	}
	return 0;
}

/*
 *	Allow the code generator to shortcut the generation of the argument
 *	of a single argument operator (for example to shortcut constant cases
 *	or simple name loads that can be done better directly)
 */
unsigned gen_uni_direct(struct node *n)
{
	return 0;
}

/*
 *	Allow the code generator to shortcut trees it knows
 */
unsigned gen_shortcut(struct node *n)
{
	return 0;
}

unsigned gen_node(struct node *n)
{
	/* Function call arguments are special - they are removed by the
	   act of call/return and reported via T_CLEANUP */
	if (n->left && n->op != T_ARGCOMMA && n->op != T_FUNCCALL)
		sp -= get_stack_size(n->left->type);
	return 0;
}