Initial commit

interpreters/bf-jit-unsafe-opt.c

@@ -0,0 +1,617 @@
+// This is an exercise in futility more than anything else
+#define _GNU_SOURCE
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <stdint.h>
+#include <stdbool.h>
+#include <assert.h>
+#include <errno.h>
+
+#if (defined __x86_64__ || defined __amd64__) && defined __unix__
+	#include <unistd.h>
+	#include <sys/mman.h>
+#else
+	#error Platform not supported
+#endif
+
+#define exit_fatal(...)                                                        \
+	do {                                                                       \
+		fprintf (stderr, "fatal: " __VA_ARGS__);                               \
+		exit (EXIT_FAILURE);                                                   \
+	} while (0)
+
+// --- Safe memory management --------------------------------------------------
+
+static void *
+xcalloc (size_t m, size_t n)
+{
+	void *p = calloc (m, n);
+	if (!p)
+		exit_fatal ("calloc: %s\n", strerror (errno));
+	return p;
+}
+
+static void *
+xrealloc (void *o, size_t n)
+{
+	void *p = realloc (o, n);
+	if (!p && n)
+		exit_fatal ("realloc: %s\n", strerror (errno));
+	return p;
+}
+
+// --- Dynamically allocated strings -------------------------------------------
+
+struct str
+{
+	char *str;                          ///< String data, null terminated
+	size_t alloc;                       ///< How many bytes are allocated
+	size_t len;                         ///< How long the string actually is
+};
+
+static void
+str_init (struct str *self)
+{
+	self->len = 0;
+	self->str = xcalloc (1, (self->alloc = 16));
+}
+
+static void
+str_ensure_space (struct str *self, size_t n)
+{
+	// We allocate at least one more byte for the terminating null character
+	size_t new_alloc = self->alloc;
+	while (new_alloc <= self->len + n)
+		new_alloc <<= 1;
+	if (new_alloc != self->alloc)
+		self->str = xrealloc (self->str, (self->alloc = new_alloc));
+}
+
+static void
+str_append_data (struct str *self, const void *data, size_t n)
+{
+	str_ensure_space (self, n);
+	memcpy (self->str + self->len, data, n);
+	self->str[self->len += n] = '\0';
+}
+
+static void
+str_append_c (struct str *self, char c)
+{
+	str_append_data (self, &c, 1);
+}
+
+// --- Application -------------------------------------------------------------
+
+enum command { RIGHT, LEFT, INC, DEC, SET, IN, OUT, BEGIN, END,
+	EAT, INCACC, DECACC };
+bool grouped[] = { 1, 1, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0 };
+struct instruction { enum command cmd; int offset; size_t arg; };
+#define INSTRUCTION(c, o, a) (struct instruction) { (c), (o), (a) }
+
+// - - Callbacks - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+
+FILE *input;                            ///< User input
+
+static int
+cin (void)
+{
+	int c = fgetc (input);
+	assert (c != EOF);
+	return c;
+}
+
+// - - Main  - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+
+#ifdef DEBUG
+static void
+debug_dump (const char *filename, struct instruction *in, size_t len)
+{
+	FILE *fp = fopen (filename, "w");
+	long indent = 0;
+	for (size_t i = 0; i < len; i++)
+	{
+		if (in[i].cmd == END)
+			indent--;
+		for (long k = 0; k < indent; k++)
+			fprintf (fp, "  ");
+
+		switch (in[i].cmd)
+		{
+		case RIGHT:  fputs ("RIGHT ", fp); break;
+		case LEFT:   fputs ("LEFT  ", fp); break;
+		case INC:    fputs ("INC   ", fp); break;
+		case DEC:    fputs ("DEC   ", fp); break;
+		case OUT:    fputs ("OUT   ", fp); break;
+		case IN:     fputs ("IN    ", fp); break;
+		case BEGIN:  fputs ("BEGIN ", fp); break;
+		case END:    fputs ("END   ", fp); break;
+		case SET:    fputs ("SET   ", fp); break;
+		case EAT:    fputs ("EAT   ", fp); break;
+		case INCACC: fputs ("INCACC", fp); break;
+		case DECACC: fputs ("DECACC", fp); break;
+		}
+		fprintf (fp, " %zu [%d]\n", in[i].arg, in[i].offset);
+		if (in[i].cmd == BEGIN)
+			indent++;
+	}
+	fclose (fp);
+}
+#else
+#define debug_dump(...)
+#endif
+
+int
+main (int argc, char *argv[])
+{
+	(void) argc;
+	(void) argv;
+
+	struct str program;
+	str_init (&program);
+
+	int c;
+	while ((c = fgetc (stdin)) != EOF)
+		str_append_c (&program, c);
+	if (ferror (stdin))
+		exit_fatal ("can't read program\n");
+	if (!(input = fopen ("/dev/tty", "rb")))
+		exit_fatal ("can't open terminal for reading\n");
+
+// - - Decode and group  - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+
+	struct instruction *parsed = xcalloc (sizeof *parsed, program.len);
+	size_t parsed_len = 0;
+
+	for (size_t i = 0; i < program.len; i++)
+	{
+		enum command cmd;
+		switch (program.str[i])
+		{
+		case '>': cmd = RIGHT; break;
+		case '<': cmd = LEFT;  break;
+		case '+': cmd = INC;   break;
+		case '-': cmd = DEC;   break;
+		case '.': cmd = OUT;   break;
+		case ',': cmd = IN;    break;
+		case '[': cmd = BEGIN; break;
+		case ']': cmd = END;   break;
+		default:  continue;
+		}
+
+		// The most basic optimization is to group identical commands together
+		if (!parsed_len || !grouped[cmd] || parsed[parsed_len - 1].cmd != cmd)
+			parsed_len++;
+
+		parsed[parsed_len - 1].cmd = cmd;
+		parsed[parsed_len - 1].arg++;
+	}
+
+// - - Optimization passes - - - - - - - - - - - - - - - - - - - - - - - - - - -
+
+	debug_dump ("bf-no-opt.txt", parsed, parsed_len);
+
+	size_t in = 0, out = 0;
+	for (; in < parsed_len; in++, out++)
+	{
+		if (in + 2 < parsed_len
+		 && parsed[in    ].cmd == BEGIN
+		 && parsed[in + 1].cmd == DEC && parsed[in + 1].arg == 1
+		 && parsed[in + 2].cmd == END)
+		{
+			parsed[out] = INSTRUCTION (SET, 0, 0);
+			in += 2;
+		}
+		else if (out && parsed[out - 1].cmd == SET && parsed[in].cmd == INC)
+			parsed[--out].arg += parsed[in].arg;
+		else if (out != in)
+			parsed[out] = parsed[in];
+	}
+	parsed_len = out;
+
+	debug_dump ("bf-pre-offsets.txt", parsed, parsed_len);
+
+	// Add offsets to INC/DEC/SET stuck between LEFT/RIGHT
+	// and compress the LEFT/RIGHT sequences
+	for (in = 0, out = 0; in < parsed_len; in++, out++)
+	{
+		ssize_t dir = 0;
+		if (parsed[in].cmd == RIGHT)
+			dir = parsed[in].arg;
+		else if (parsed[in].cmd == LEFT)
+			dir = -(ssize_t) parsed[in].arg;
+		else
+		{
+			parsed[out] = parsed[in];
+			continue;
+		}
+
+		while (in + 2 < parsed_len)
+		{
+			// An immediate offset has its limits
+			if (dir < INT8_MIN || dir > INT8_MAX)
+				break;
+
+			ssize_t diff;
+			if (parsed[in + 2].cmd == RIGHT)
+				diff = parsed[in + 2].arg;
+			else if (parsed[in + 2].cmd == LEFT)
+				diff = -(ssize_t) parsed[in + 2].arg;
+			else
+				break;
+
+			int cmd = parsed[in + 1].cmd;
+			if (cmd != INC && cmd != DEC && cmd != SET)
+				break;
+
+			parsed[out] = parsed[in + 1];
+			parsed[out].offset = dir;
+
+			dir += diff;
+			out += 1;
+			in += 2;
+		}
+
+		for (; in + 1 < parsed_len; in++)
+		{
+			if (parsed[in + 1].cmd == RIGHT)
+				dir += parsed[in + 1].arg;
+			else if (parsed[in + 1].cmd == LEFT)
+				dir -= (ssize_t) parsed[in + 1].arg;
+			else
+				break;
+		}
+
+		if (!dir)
+			out--;
+		else if (dir > 0)
+			parsed[out] = INSTRUCTION (RIGHT, 0, dir);
+		else
+			parsed[out] = INSTRUCTION (LEFT, 0, -dir);
+	}
+	parsed_len = out;
+
+	debug_dump ("bf-pre-incdec-unloop.txt", parsed, parsed_len);
+
+	// Try to eliminate loops that eat a cell and add/subtract its value
+	// to/from some other cell
+	for (in = 0, out = 0; in < parsed_len; in++, out++)
+	{
+		parsed[out] = parsed[in];
+		if (parsed[in].cmd != BEGIN)
+			continue;
+
+		bool ok = false;
+		size_t count = 0;
+		for (size_t k = in + 1; k < parsed_len; k++)
+		{
+			if (parsed[k].cmd == END)
+			{
+				ok = true;
+				break;
+			}
+			if (parsed[k].cmd != INC
+			 && parsed[k].cmd != DEC)
+				break;
+			count++;
+		}
+		if (!ok)
+			continue;
+
+		// Stable sort operations by their offsets, put [0] first
+		bool sorted;
+		do
+		{
+			sorted = true;
+			for (size_t k = 1; k < count; k++)
+			{
+				if (parsed[in + k].offset == 0)
+					continue;
+				if (parsed[in + k + 1].offset != 0
+				 && parsed[in + k].offset <= parsed[in + k + 1].offset)
+					continue;
+
+				struct instruction tmp = parsed[in + k + 1];
+				parsed[in + k + 1] = parsed[in + k];
+				parsed[in + k] = tmp;
+				sorted = false;
+			}
+		}
+		while (!sorted);
+
+		// Abort the optimization on duplicate offsets (complication with [0])
+		for (size_t k = 1; k < count; k++)
+			if (parsed[in + k].offset == parsed[in + k + 1].offset)
+				ok = false;
+		// XXX: can't make the code longer either
+		for (size_t k = 1; k <= count; k++)
+			if (parsed[in + k].arg != 1)
+				ok = false;
+		if (!ok
+		 || parsed[in + 1].cmd != DEC
+		 || parsed[in + 1].offset != 0)
+			continue;
+
+		int min_safe_left_offset = 0;
+		if (in > 1 && parsed[in - 1].cmd == RIGHT)
+			min_safe_left_offset = -parsed[in - 1].arg;
+
+		bool cond_needed_for_safety = false;
+		for (size_t k = 0; k < count; k++)
+			if (parsed[in + k + 1].offset < min_safe_left_offset)
+			{
+				cond_needed_for_safety = true;
+				break;
+			}
+
+		in++;
+		if (cond_needed_for_safety)
+			out++;
+
+		parsed[out] = INSTRUCTION (EAT, 0, 0);
+		for (size_t k = 1; k < count; k++)
+			parsed[out + k] = INSTRUCTION (parsed[in + k].cmd == INC
+				? INCACC : DECACC, parsed[in + k].offset, 0);
+
+		in += count;
+		out += count;
+
+		if (cond_needed_for_safety)
+			parsed[out] = INSTRUCTION (END, 0, 0);
+		else
+			out--;
+	}
+	parsed_len = out;
+
+	debug_dump ("bf-optimized.txt", parsed, parsed_len);
+
+// - - Loop pairing  - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+
+	size_t nesting = 0;
+	size_t *stack = xcalloc (sizeof *stack, parsed_len);
+	for (size_t i = 0; i < parsed_len; i++)
+	{
+		switch (parsed[i].cmd)
+		{
+		case BEGIN:
+			stack[nesting++] = i;
+			break;
+		case END:
+			assert (nesting > 0);
+
+			--nesting;
+			parsed[stack[nesting]].arg = i + 1;
+
+			// Looping can be disabled by optimizations
+			if (parsed[i].arg)
+				parsed[i].arg = stack[nesting] + 1;
+		default:
+			break;
+		}
+	}
+	free (stack);
+	assert (nesting == 0);
+
+	debug_dump ("bf-final.txt", parsed, parsed_len);
+
+// - - JIT - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+
+	// Functions preserve the registers rbx, rsp, rbp, r12, r13, r14, and r15;
+	// while rax, rdi, rsi, rdx, rcx, r8, r9, r10, r11 are scratch registers.
+
+	str_init (&program);
+	size_t *offsets = xcalloc (sizeof *offsets, parsed_len + 1);
+	uint8_t *arith  = xcalloc (sizeof *arith,   parsed_len);
+
+#define CODE(x) { char t[] = x; str_append_data (&program, t, sizeof t - 1); }
+#define WORD(x) { size_t t = (size_t)(x); str_append_data (&program, &t, 8); }
+#define DWRD(x) { size_t t = (size_t)(x); str_append_data (&program, &t, 4); }
+
+	CODE ("\x48\x89\xF8")                     // mov rax, rdi
+	CODE ("\x30\xDB")                         // xor bl, bl
+
+	for (size_t i = 0; i < parsed_len; i++)
+	{
+		offsets[i] = program.len;
+
+		size_t arg = parsed[i].arg;
+		assert (arg <= UINT32_MAX);
+
+		int offset = parsed[i].offset;
+		assert (offset <= INT8_MAX && offset >= INT8_MIN);
+
+		// Don't save what we've just loaded
+		if (parsed[i].cmd == LEFT || parsed[i].cmd == RIGHT)
+			if (i < 2 || i + 1 >= parsed_len
+			 || (parsed[i - 2].cmd != LEFT && parsed[i - 2].cmd != RIGHT)
+			 || parsed[i - 1].cmd != BEGIN
+			 || parsed[i + 1].cmd != END)
+				CODE ("\x88\x18")             // mov [rax], bl
+
+		switch (parsed[i].cmd)
+		{
+		case RIGHT:
+			// add rax, "arg" -- optimistic, no boundary checking
+			if (arg > INT8_MAX)
+				{ CODE ("\x48\x05")     DWRD (arg) }
+			else
+				{ CODE ("\x48\x83\xC0") str_append_c (&program, arg); }
+			break;
+		case LEFT:
+			// sub rax, "arg" -- optimistic, no boundary checking
+			if (arg > INT8_MAX)
+				{ CODE ("\x48\x2D")     DWRD (arg) }
+			else
+				{ CODE ("\x48\x83\xE8") str_append_c (&program, arg); }
+			break;
+
+		case EAT:
+			CODE ("\x41\x88\xDC")             // mov r12b, bl
+			CODE ("\x30\xDB")                 // xor bl, bl
+			arith[i] = 1;
+			break;
+		case INCACC:
+			if (offset)
+			{
+				CODE ("\x44\x00\x60")         // add [rax+"offset"], r12b
+				str_append_c (&program, offset);
+			}
+			else
+			{
+				CODE ("\x44\x00\xE3")         // add bl, r12b
+				arith[i] = 1;
+			}
+			break;
+		case DECACC:
+			if (offset)
+			{
+				CODE ("\x44\x28\x60")         // sub [rax+"offset"], r12b
+				str_append_c (&program, offset);
+			}
+			else
+			{
+				CODE ("\x44\x28\xE3")         // sub bl, r12b
+				arith[i] = 1;
+			}
+			break;
+
+		case INC:
+			if (offset)
+			{
+				CODE ("\x80\x40")             // add byte [rax+"offset"], "arg"
+				str_append_c (&program, offset);
+			}
+			else
+			{
+				arith[i] = 1;
+				CODE ("\x80\xC3")             // add bl, "arg"
+			}
+			str_append_c (&program, arg);
+			break;
+		case DEC:
+			if (offset)
+			{
+				CODE ("\x80\x68")             // sub byte [rax+"offset"], "arg"
+				str_append_c (&program, offset);
+			}
+			else
+			{
+				arith[i] = 1;
+				CODE ("\x80\xEB")             // sub bl, "arg"
+			}
+			str_append_c (&program, arg);
+			break;
+		case SET:
+			if (offset)
+			{
+				CODE ("\xC6\x40")             // mov byte [rax+"offset"], "arg"
+				str_append_c (&program, offset);
+			}
+			else
+				CODE ("\xB3")                 // mov bl, "arg"
+			str_append_c (&program, arg);
+			break;
+
+		case OUT:
+			CODE ("\x50\x53")                 // push rax, push rbx
+			CODE ("\x48\x0F\xB6\xFB")         // movzx rdi, bl
+			CODE ("\x48\xBE") WORD (stdout)   // mov rsi, "stdout"
+			CODE ("\x48\xB8") WORD (fputc)    // mov rax, "fputc"
+			CODE ("\xFF\xD0")                 // call rax
+			CODE ("\x5B\x58")                 // pop rbx, pop rax
+			break;
+		case IN:
+			CODE ("\x50")                     // push rax
+			CODE ("\x48\xB8") WORD (cin)      // mov rax, "cin"
+			CODE ("\xFF\xD0")                 // call rax
+			CODE ("\x88\xC3")                 // mov bl, al
+			CODE ("\x58")                     // pop rax
+			break;
+
+		case BEGIN:
+			// Don't test the register when the flag has been set already;
+			// this doesn't have much of an effect in practice
+			if (!i || !arith[i - 1])
+				CODE ("\x84\xDB")             // test bl, bl
+			CODE ("\x0F\x84\x00\x00\x00\x00") // jz "offsets[i]"
+			break;
+		case END:
+			// We know that the cell is zero, make this an "if", not a "loop";
+			// this doesn't have much of an effect in practice
+			if (!arg)
+				break;
+
+			if (!i || !arith[i - 1])
+				CODE ("\x84\xDB")             // test bl, bl
+			CODE ("\x0F\x85\x00\x00\x00\x00") // jnz "offsets[i]"
+			break;
+		}
+
+		// No sense in reading it out when we overwrite it immediately;
+		// this doesn't have much of an effect in practice
+		if (parsed[i].cmd == LEFT || parsed[i].cmd == RIGHT)
+			if (i + 1 >= parsed_len
+			 || parsed[i + 1].cmd != SET
+			 || parsed[i + 1].offset != 0)
+				CODE ("\x8A\x18")             // mov bl, [rax]
+	}
+	// When there is a loop at the end we need to be able to jump past it
+	offsets[parsed_len] = program.len;
+	str_append_c (&program, '\xC3');          // ret
+
+	// Now that we know where each instruction is, fill in relative jumps;
+	// this must accurately reflect code generators for BEGIN and END
+	for (size_t i = 0; i < parsed_len; i++)
+	{
+		if ((parsed[i].cmd != BEGIN && parsed[i].cmd != END)
+		 || !parsed[i].arg)
+			continue;
+
+		size_t fixup = offsets[i] + 2;
+		if (!i || !arith[i - 1])
+			fixup += 2;
+
+		*(int32_t *)(program.str + fixup) =
+			((intptr_t)(offsets[parsed[i].arg]) - (intptr_t)(fixup + 4));
+	}
+	free (offsets);
+	free (arith);
+
+#ifdef DEBUG
+	FILE *bin = fopen ("bf-jit.bin", "w");
+	fwrite (program.str, program.len, 1, bin);
+	fclose (bin);
+#endif
+
+// - - Runtime - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+
+	// Some systems may have W^X
+	void *executable = mmap (NULL, program.len, PROT_READ | PROT_WRITE,
+		MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+	if (!executable)
+		exit_fatal ("mmap: %s\n", strerror (errno));
+
+	memcpy (executable, program.str, program.len);
+	if (mprotect (executable, program.len, PROT_READ | PROT_EXEC))
+		exit_fatal ("mprotect: %s\n", strerror (errno));
+
+	// We create crash zones on both ends of the tape for some minimum safety
+	long pagesz = sysconf (_SC_PAGESIZE);
+	assert (pagesz > 0);
+
+	const size_t tape_len = (1 << 20) + 2 * pagesz;
+	char *tape = mmap (NULL, tape_len, PROT_READ | PROT_WRITE,
+		MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+	if (!tape)
+		exit_fatal ("mmap: %s\n", strerror (errno));
+
+	memset (tape, 0, tape_len);
+	if (mprotect (tape,                     pagesz, PROT_NONE)
+	 || mprotect (tape + tape_len - pagesz, pagesz, PROT_NONE))
+		exit_fatal ("mprotect: %s\n", strerror (errno));
+
+	((void (*) (char *)) executable)(tape + pagesz);
+	return 0;
+}