Move peephole optimizer to separate file.

1 files changed, 615 insertions, 0 deletions

diff --git a/Python/peephole.c b/Python/peephole.c
new file mode 100644
index 0000000..1d94319
--- /dev/null
+++ b/Python/peephole.c
@@ -0,0 +1,615 @@
+/* Peehole optimizations for bytecode compiler. */
+
+#include "Python.h"
+
+#include "Python-ast.h"
+#include "node.h"
+#include "pyarena.h"
+#include "ast.h"
+#include "code.h"
+#include "compile.h"
+#include "symtable.h"
+#include "opcode.h"
+
+#define GETARG(arr, i) ((int)((arr[i+2]<<8) + arr[i+1]))
+#define UNCONDITIONAL_JUMP(op)	(op==JUMP_ABSOLUTE || op==JUMP_FORWARD)
+#define ABSOLUTE_JUMP(op) (op==JUMP_ABSOLUTE || op==CONTINUE_LOOP)
+#define GETJUMPTGT(arr, i) (GETARG(arr,i) + (ABSOLUTE_JUMP(arr[i]) ? 0 : i+3))
+#define SETARG(arr, i, val) arr[i+2] = val>>8; arr[i+1] = val & 255
+#define CODESIZE(op)  (HAS_ARG(op) ? 3 : 1)
+#define ISBASICBLOCK(blocks, start, bytes) \
+	(blocks[start]==blocks[start+bytes-1])
+
+/* Replace LOAD_CONST c1. LOAD_CONST c2 ... LOAD_CONST cn BUILD_TUPLE n
+   with	   LOAD_CONST (c1, c2, ... cn).
+   The consts table must still be in list form so that the
+   new constant (c1, c2, ... cn) can be appended.
+   Called with codestr pointing to the first LOAD_CONST.
+   Bails out with no change if one or more of the LOAD_CONSTs is missing. 
+   Also works for BUILD_LIST when followed by an "in" or "not in" test.
+*/
+static int
+tuple_of_constants(unsigned char *codestr, int n, PyObject *consts)
+{
+	PyObject *newconst, *constant;
+	Py_ssize_t i, arg, len_consts;
+
+	/* Pre-conditions */
+	assert(PyList_CheckExact(consts));
+	assert(codestr[n*3] == BUILD_TUPLE || codestr[n*3] == BUILD_LIST);
+	assert(GETARG(codestr, (n*3)) == n);
+	for (i=0 ; i<n ; i++)
+		assert(codestr[i*3] == LOAD_CONST);
+
+	/* Buildup new tuple of constants */
+	newconst = PyTuple_New(n);
+	if (newconst == NULL)
+		return 0;
+	len_consts = PyList_GET_SIZE(consts);
+	for (i=0 ; i<n ; i++) {
+		arg = GETARG(codestr, (i*3));
+		assert(arg < len_consts);
+		constant = PyList_GET_ITEM(consts, arg);
+		Py_INCREF(constant);
+		PyTuple_SET_ITEM(newconst, i, constant);
+	}
+
+	/* Append folded constant onto consts */
+	if (PyList_Append(consts, newconst)) {
+		Py_DECREF(newconst);
+		return 0;
+	}
+	Py_DECREF(newconst);
+
+	/* Write NOPs over old LOAD_CONSTS and
+	   add a new LOAD_CONST newconst on top of the BUILD_TUPLE n */
+	memset(codestr, NOP, n*3);
+	codestr[n*3] = LOAD_CONST;
+	SETARG(codestr, (n*3), len_consts);
+	return 1;
+}
+
+/* Replace LOAD_CONST c1. LOAD_CONST c2 BINOP
+   with	   LOAD_CONST binop(c1,c2)
+   The consts table must still be in list form so that the
+   new constant can be appended.
+   Called with codestr pointing to the first LOAD_CONST. 
+   Abandons the transformation if the folding fails (i.e.  1+'a').  
+   If the new constant is a sequence, only folds when the size
+   is below a threshold value.	That keeps pyc files from
+   becoming large in the presence of code like:	 (None,)*1000.
+*/
+static int
+fold_binops_on_constants(unsigned char *codestr, PyObject *consts)
+{
+	PyObject *newconst, *v, *w;
+	Py_ssize_t len_consts, size;
+	int opcode;
+
+	/* Pre-conditions */
+	assert(PyList_CheckExact(consts));
+	assert(codestr[0] == LOAD_CONST);
+	assert(codestr[3] == LOAD_CONST);
+
+	/* Create new constant */
+	v = PyList_GET_ITEM(consts, GETARG(codestr, 0));
+	w = PyList_GET_ITEM(consts, GETARG(codestr, 3));
+	opcode = codestr[6];
+	switch (opcode) {
+		case BINARY_POWER:
+			newconst = PyNumber_Power(v, w, Py_None);
+			break;
+		case BINARY_MULTIPLY:
+			newconst = PyNumber_Multiply(v, w);
+			break;
+		case BINARY_DIVIDE:
+			/* Cannot fold this operation statically since
+                           the result can depend on the run-time presence
+                           of the -Qnew flag */
+			return 0;
+		case BINARY_TRUE_DIVIDE:
+			newconst = PyNumber_TrueDivide(v, w);
+			break;
+		case BINARY_FLOOR_DIVIDE:
+			newconst = PyNumber_FloorDivide(v, w);
+			break;
+		case BINARY_MODULO:
+			newconst = PyNumber_Remainder(v, w);
+			break;
+		case BINARY_ADD:
+			newconst = PyNumber_Add(v, w);
+			break;
+		case BINARY_SUBTRACT:
+			newconst = PyNumber_Subtract(v, w);
+			break;
+		case BINARY_SUBSCR:
+			newconst = PyObject_GetItem(v, w);
+			break;
+		case BINARY_LSHIFT:
+			newconst = PyNumber_Lshift(v, w);
+			break;
+		case BINARY_RSHIFT:
+			newconst = PyNumber_Rshift(v, w);
+			break;
+		case BINARY_AND:
+			newconst = PyNumber_And(v, w);
+			break;
+		case BINARY_XOR:
+			newconst = PyNumber_Xor(v, w);
+			break;
+		case BINARY_OR:
+			newconst = PyNumber_Or(v, w);
+			break;
+		default:
+			/* Called with an unknown opcode */
+			PyErr_Format(PyExc_SystemError,
+			     "unexpected binary operation %d on a constant",
+				     opcode);
+			return 0;
+	}
+	if (newconst == NULL) {
+		PyErr_Clear();
+		return 0;
+	}
+	size = PyObject_Size(newconst);
+	if (size == -1)
+		PyErr_Clear();
+	else if (size > 20) {
+		Py_DECREF(newconst);
+		return 0;
+	}
+
+	/* Append folded constant into consts table */
+	len_consts = PyList_GET_SIZE(consts);
+	if (PyList_Append(consts, newconst)) {
+		Py_DECREF(newconst);
+		return 0;
+	}
+	Py_DECREF(newconst);
+
+	/* Write NOP NOP NOP NOP LOAD_CONST newconst */
+	memset(codestr, NOP, 4);
+	codestr[4] = LOAD_CONST;
+	SETARG(codestr, 4, len_consts);
+	return 1;
+}
+
+static int
+fold_unaryops_on_constants(unsigned char *codestr, PyObject *consts)
+{
+	PyObject *newconst=NULL, *v;
+	Py_ssize_t len_consts;
+	int opcode;
+
+	/* Pre-conditions */
+	assert(PyList_CheckExact(consts));
+	assert(codestr[0] == LOAD_CONST);
+
+	/* Create new constant */
+	v = PyList_GET_ITEM(consts, GETARG(codestr, 0));
+	opcode = codestr[3];
+	switch (opcode) {
+		case UNARY_NEGATIVE:
+			/* Preserve the sign of -0.0 */
+			if (PyObject_IsTrue(v) == 1)
+				newconst = PyNumber_Negative(v);
+			break;
+		case UNARY_CONVERT:
+			newconst = PyObject_Repr(v);
+			break;
+		case UNARY_INVERT:
+			newconst = PyNumber_Invert(v);
+			break;
+		default:
+			/* Called with an unknown opcode */
+			PyErr_Format(PyExc_SystemError,
+			     "unexpected unary operation %d on a constant",
+				     opcode);
+			return 0;
+	}
+	if (newconst == NULL) {
+		PyErr_Clear();
+		return 0;
+	}
+
+	/* Append folded constant into consts table */
+	len_consts = PyList_GET_SIZE(consts);
+	if (PyList_Append(consts, newconst)) {
+		Py_DECREF(newconst);
+		return 0;
+	}
+	Py_DECREF(newconst);
+
+	/* Write NOP LOAD_CONST newconst */
+	codestr[0] = NOP;
+	codestr[1] = LOAD_CONST;
+	SETARG(codestr, 1, len_consts);
+	return 1;
+}
+
+static unsigned int *
+markblocks(unsigned char *code, int len)
+{
+	unsigned int *blocks = (unsigned int *)PyMem_Malloc(len*sizeof(int));
+	int i,j, opcode, blockcnt = 0;
+
+	if (blocks == NULL) {
+		PyErr_NoMemory();
+		return NULL;
+	}
+	memset(blocks, 0, len*sizeof(int));
+
+	/* Mark labels in the first pass */
+	for (i=0 ; i<len ; i+=CODESIZE(opcode)) {
+		opcode = code[i];
+		switch (opcode) {
+			case FOR_ITER:
+			case JUMP_FORWARD:
+			case JUMP_IF_FALSE:
+			case JUMP_IF_TRUE:
+			case JUMP_ABSOLUTE:
+			case CONTINUE_LOOP:
+			case SETUP_LOOP:
+			case SETUP_EXCEPT:
+			case SETUP_FINALLY:
+				j = GETJUMPTGT(code, i);
+				blocks[j] = 1;
+				break;
+		}
+	}
+	/* Build block numbers in the second pass */
+	for (i=0 ; i<len ; i++) {
+		blockcnt += blocks[i];	/* increment blockcnt over labels */
+		blocks[i] = blockcnt;
+	}
+	return blocks;
+}
+
+/* Perform basic peephole optimizations to components of a code object.
+   The consts object should still be in list form to allow new constants 
+   to be appended.
+
+   To keep the optimizer simple, it bails out (does nothing) for code
+   containing extended arguments or that has a length over 32,700.  That 
+   allows us to avoid overflow and sign issues.	 Likewise, it bails when
+   the lineno table has complex encoding for gaps >= 255.
+
+   Optimizations are restricted to simple transformations occuring within a
+   single basic block.	All transformations keep the code size the same or 
+   smaller.  For those that reduce size, the gaps are initially filled with 
+   NOPs.  Later those NOPs are removed and the jump addresses retargeted in 
+   a single pass.  Line numbering is adjusted accordingly. */
+
+PyObject *
+PyCode_Optimize(PyObject *code, PyObject* consts, PyObject *names,
+                PyObject *lineno_obj)
+{
+	Py_ssize_t i, j, codelen;
+	int nops, h, adj;
+	int tgt, tgttgt, opcode;
+	unsigned char *codestr = NULL;
+	unsigned char *lineno;
+	int *addrmap = NULL;
+	int new_line, cum_orig_line, last_line, tabsiz;
+	int cumlc=0, lastlc=0;	/* Count runs of consecutive LOAD_CONSTs */
+	unsigned int *blocks = NULL;
+	char *name;
+
+	/* Bail out if an exception is set */
+	if (PyErr_Occurred())
+		goto exitUnchanged;
+
+	/* Bypass optimization when the lineno table is too complex */
+	assert(PyString_Check(lineno_obj));
+	lineno = (unsigned char*)PyString_AS_STRING(lineno_obj);
+	tabsiz = PyString_GET_SIZE(lineno_obj);
+	if (memchr(lineno, 255, tabsiz) != NULL)
+		goto exitUnchanged;
+
+	/* Avoid situations where jump retargeting could overflow */
+	assert(PyString_Check(code));
+	codelen = PyString_Size(code);
+	if (codelen > 32700)
+		goto exitUnchanged;
+
+	/* Make a modifiable copy of the code string */
+	codestr = (unsigned char *)PyMem_Malloc(codelen);
+	if (codestr == NULL)
+		goto exitUnchanged;
+	codestr = (unsigned char *)memcpy(codestr, 
+                                        PyString_AS_STRING(code), codelen);
+
+	/* Verify that RETURN_VALUE terminates the codestring.	This allows
+	   the various transformation patterns to look ahead several
+	   instructions without additional checks to make sure they are not
+	   looking beyond the end of the code string.
+	*/
+	if (codestr[codelen-1] != RETURN_VALUE)
+		goto exitUnchanged;
+
+	/* Mapping to new jump targets after NOPs are removed */
+	addrmap = (int *)PyMem_Malloc(codelen * sizeof(int));
+	if (addrmap == NULL)
+		goto exitUnchanged;
+
+	blocks = markblocks(codestr, codelen);
+	if (blocks == NULL)
+		goto exitUnchanged;
+	assert(PyList_Check(consts));
+
+	for (i=0 ; i<codelen ; i += CODESIZE(codestr[i])) {
+		opcode = codestr[i];
+
+		lastlc = cumlc;
+		cumlc = 0;
+
+		switch (opcode) {
+
+			/* Replace UNARY_NOT JUMP_IF_FALSE POP_TOP with 
+			   with	   JUMP_IF_TRUE POP_TOP */
+			case UNARY_NOT:
+				if (codestr[i+1] != JUMP_IF_FALSE  ||
+				    codestr[i+4] != POP_TOP  ||
+				    !ISBASICBLOCK(blocks,i,5))
+					continue;
+				tgt = GETJUMPTGT(codestr, (i+1));
+				if (codestr[tgt] != POP_TOP)
+					continue;
+				j = GETARG(codestr, i+1) + 1;
+				codestr[i] = JUMP_IF_TRUE;
+				SETARG(codestr, i, j);
+				codestr[i+3] = POP_TOP;
+				codestr[i+4] = NOP;
+				break;
+
+				/* not a is b -->  a is not b
+				   not a in b -->  a not in b
+				   not a is not b -->  a is b
+				   not a not in b -->  a in b
+				*/
+			case COMPARE_OP:
+				j = GETARG(codestr, i);
+				if (j < 6  ||  j > 9  ||
+				    codestr[i+3] != UNARY_NOT  || 
+				    !ISBASICBLOCK(blocks,i,4))
+					continue;
+				SETARG(codestr, i, (j^1));
+				codestr[i+3] = NOP;
+				break;
+
+				/* Replace LOAD_GLOBAL/LOAD_NAME None
+                                   with LOAD_CONST None */
+			case LOAD_NAME:
+			case LOAD_GLOBAL:
+				j = GETARG(codestr, i);
+				name = PyString_AsString(PyTuple_GET_ITEM(names, j));
+				if (name == NULL  ||  strcmp(name, "None") != 0)
+					continue;
+				for (j=0 ; j < PyList_GET_SIZE(consts) ; j++) {
+					if (PyList_GET_ITEM(consts, j) == Py_None) {
+						codestr[i] = LOAD_CONST;
+						SETARG(codestr, i, j);
+						cumlc = lastlc + 1;
+						break;
+					}
+				}
+				break;
+
+				/* Skip over LOAD_CONST trueconst
+                                   JUMP_IF_FALSE xx  POP_TOP */
+			case LOAD_CONST:
+				cumlc = lastlc + 1;
+				j = GETARG(codestr, i);
+				if (codestr[i+3] != JUMP_IF_FALSE  ||
+				    codestr[i+6] != POP_TOP  ||
+				    !ISBASICBLOCK(blocks,i,7)  ||
+				    !PyObject_IsTrue(PyList_GET_ITEM(consts, j)))
+					continue;
+				memset(codestr+i, NOP, 7);
+				cumlc = 0;
+				break;
+
+				/* Try to fold tuples of constants (includes a case for lists
+				   which are only used for "in" and "not in" tests).
+				   Skip over BUILD_SEQN 1 UNPACK_SEQN 1.
+				   Replace BUILD_SEQN 2 UNPACK_SEQN 2 with ROT2.
+				   Replace BUILD_SEQN 3 UNPACK_SEQN 3 with ROT3 ROT2. */
+			case BUILD_TUPLE:
+			case BUILD_LIST:
+				j = GETARG(codestr, i);
+				h = i - 3 * j;
+				if (h >= 0  &&
+				    j <= lastlc	 &&
+				    ((opcode == BUILD_TUPLE && 
+				      ISBASICBLOCK(blocks, h, 3*(j+1))) ||
+				     (opcode == BUILD_LIST && 
+				      codestr[i+3]==COMPARE_OP && 
+				      ISBASICBLOCK(blocks, h, 3*(j+2)) &&
+				      (GETARG(codestr,i+3)==6 ||
+				       GETARG(codestr,i+3)==7))) &&
+				    tuple_of_constants(&codestr[h], j, consts)) {
+					assert(codestr[i] == LOAD_CONST);
+					cumlc = 1;
+					break;
+				}
+				if (codestr[i+3] != UNPACK_SEQUENCE  ||
+				    !ISBASICBLOCK(blocks,i,6) ||
+				    j != GETARG(codestr, i+3))
+					continue;
+				if (j == 1) {
+					memset(codestr+i, NOP, 6);
+				} else if (j == 2) {
+					codestr[i] = ROT_TWO;
+					memset(codestr+i+1, NOP, 5);
+				} else if (j == 3) {
+					codestr[i] = ROT_THREE;
+					codestr[i+1] = ROT_TWO;
+					memset(codestr+i+2, NOP, 4);
+				}
+				break;
+
+				/* Fold binary ops on constants.
+				   LOAD_CONST c1 LOAD_CONST c2 BINOP -->  LOAD_CONST binop(c1,c2) */
+			case BINARY_POWER:
+			case BINARY_MULTIPLY:
+			case BINARY_TRUE_DIVIDE:
+			case BINARY_FLOOR_DIVIDE:
+			case BINARY_MODULO:
+			case BINARY_ADD:
+			case BINARY_SUBTRACT:
+			case BINARY_SUBSCR:
+			case BINARY_LSHIFT:
+			case BINARY_RSHIFT:
+			case BINARY_AND:
+			case BINARY_XOR:
+			case BINARY_OR:
+				if (lastlc >= 2	 &&
+				    ISBASICBLOCK(blocks, i-6, 7)  &&
+				    fold_binops_on_constants(&codestr[i-6], consts)) {
+					i -= 2;
+					assert(codestr[i] == LOAD_CONST);
+					cumlc = 1;
+				}
+				break;
+
+				/* Fold unary ops on constants.
+				   LOAD_CONST c1  UNARY_OP -->	LOAD_CONST unary_op(c) */
+			case UNARY_NEGATIVE:
+			case UNARY_CONVERT:
+			case UNARY_INVERT:
+				if (lastlc >= 1	 &&
+				    ISBASICBLOCK(blocks, i-3, 4)  &&
+				    fold_unaryops_on_constants(&codestr[i-3], consts))	{
+					i -= 2;
+					assert(codestr[i] == LOAD_CONST);
+					cumlc = 1;
+				}
+				break;
+
+				/* Simplify conditional jump to conditional jump where the
+				   result of the first test implies the success of a similar
+				   test or the failure of the opposite test.
+				   Arises in code like:
+				   "if a and b:"
+				   "if a or b:"
+				   "a and b or c"
+				   "(a and b) and c"
+				   x:JUMP_IF_FALSE y   y:JUMP_IF_FALSE z  -->  x:JUMP_IF_FALSE z
+				   x:JUMP_IF_FALSE y   y:JUMP_IF_TRUE z	 -->  x:JUMP_IF_FALSE y+3
+				   where y+3 is the instruction following the second test.
+				*/
+			case JUMP_IF_FALSE:
+			case JUMP_IF_TRUE:
+				tgt = GETJUMPTGT(codestr, i);
+				j = codestr[tgt];
+				if (j == JUMP_IF_FALSE	||  j == JUMP_IF_TRUE) {
+					if (j == opcode) {
+						tgttgt = GETJUMPTGT(codestr, tgt) - i - 3;
+						SETARG(codestr, i, tgttgt);
+					} else {
+						tgt -= i;
+						SETARG(codestr, i, tgt);
+					}
+					break;
+				}
+				/* Intentional fallthrough */  
+
+				/* Replace jumps to unconditional jumps */
+			case FOR_ITER:
+			case JUMP_FORWARD:
+			case JUMP_ABSOLUTE:
+			case CONTINUE_LOOP:
+			case SETUP_LOOP:
+			case SETUP_EXCEPT:
+			case SETUP_FINALLY:
+				tgt = GETJUMPTGT(codestr, i);
+				if (!UNCONDITIONAL_JUMP(codestr[tgt]))
+					continue;
+				tgttgt = GETJUMPTGT(codestr, tgt);
+				if (opcode == JUMP_FORWARD) /* JMP_ABS can go backwards */
+					opcode = JUMP_ABSOLUTE;
+				if (!ABSOLUTE_JUMP(opcode))
+					tgttgt -= i + 3;     /* Calc relative jump addr */
+				if (tgttgt < 0)		  /* No backward relative jumps */
+					continue;
+				codestr[i] = opcode;
+				SETARG(codestr, i, tgttgt);
+				break;
+
+			case EXTENDED_ARG:
+				goto exitUnchanged;
+
+				/* Replace RETURN LOAD_CONST None RETURN with just RETURN */
+			case RETURN_VALUE:
+				if (i+4 >= codelen  ||
+				    codestr[i+4] != RETURN_VALUE	 ||
+				    !ISBASICBLOCK(blocks,i,5))
+					continue;
+				memset(codestr+i+1, NOP, 4);
+				break;
+		}
+	}
+
+	/* Fixup linenotab */
+	for (i=0, nops=0 ; i<codelen ; i += CODESIZE(codestr[i])) {
+		addrmap[i] = i - nops;
+		if (codestr[i] == NOP)
+			nops++;
+	}
+	cum_orig_line = 0;
+	last_line = 0;
+	for (i=0 ; i < tabsiz ; i+=2) {
+		cum_orig_line += lineno[i];
+		new_line = addrmap[cum_orig_line];
+		assert (new_line - last_line < 255);
+		lineno[i] =((unsigned char)(new_line - last_line));
+		last_line = new_line;
+	}
+
+	/* Remove NOPs and fixup jump targets */
+	for (i=0, h=0 ; i<codelen ; ) {
+		opcode = codestr[i];
+		switch (opcode) {
+			case NOP:
+				i++;
+				continue;
+
+			case JUMP_ABSOLUTE:
+			case CONTINUE_LOOP:
+				j = addrmap[GETARG(codestr, i)];
+				SETARG(codestr, i, j);
+				break;
+
+			case FOR_ITER:
+			case JUMP_FORWARD:
+			case JUMP_IF_FALSE:
+			case JUMP_IF_TRUE:
+			case SETUP_LOOP:
+			case SETUP_EXCEPT:
+			case SETUP_FINALLY:
+				j = addrmap[GETARG(codestr, i) + i + 3] - addrmap[i] - 3;
+				SETARG(codestr, i, j);
+				break;
+		}
+		adj = CODESIZE(opcode);
+		while (adj--)
+			codestr[h++] = codestr[i++];
+	}
+	assert(h + nops == codelen);
+
+	code = PyString_FromStringAndSize((char *)codestr, h);
+	PyMem_Free(addrmap);
+	PyMem_Free(codestr);
+	PyMem_Free(blocks);
+	return code;
+
+ exitUnchanged:
+	if (blocks != NULL)
+		PyMem_Free(blocks);
+	if (addrmap != NULL)
+		PyMem_Free(addrmap);
+	if (codestr != NULL)
+		PyMem_Free(codestr);
+	Py_INCREF(code);
+	return code;
+}