From f4cf76dd5eabd8af5d2a866da1f75fa745aa6f29 Mon Sep 17 00:00:00 2001
From: Raymond Hettinger <python@rcn.com>
Date: Thu, 24 Apr 2003 05:45:23 +0000
Subject: Revert the previous enhancement to the bytecode optimizer. The
 additional code complexity and new NOP opcode were not worth it.

---
 Include/opcode.h |  2 --
 Lib/opcode.py    |  2 --
 Misc/NEWS        |  7 -----
 Python/ceval.c   |  3 --
 Python/compile.c | 92 ++++++--------------------------------------------------
 5 files changed, 9 insertions(+), 97 deletions(-)

diff --git a/Include/opcode.h b/Include/opcode.h
index 9f7d263..2f3dd04 100644
--- a/Include/opcode.h
+++ b/Include/opcode.h
@@ -14,8 +14,6 @@ extern "C" {
 #define DUP_TOP		4
 #define ROT_FOUR	5
 
-#define NOP		9
-
 #define UNARY_POSITIVE	10
 #define UNARY_NEGATIVE	11
 #define UNARY_NOT	12
diff --git a/Lib/opcode.py b/Lib/opcode.py
index 15f92a7..cfde5f8 100644
--- a/Lib/opcode.py
+++ b/Lib/opcode.py
@@ -49,8 +49,6 @@ def_op('ROT_THREE', 3)
 def_op('DUP_TOP', 4)
 def_op('ROT_FOUR', 5)
 
-def_op('NOP', 9)
-
 def_op('UNARY_POSITIVE', 10)
 def_op('UNARY_NEGATIVE', 11)
 def_op('UNARY_NOT', 12)
diff --git a/Misc/NEWS b/Misc/NEWS
index 4996f1b..65ad925 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -306,13 +306,6 @@ Core and builtins
   value, but according to PEP 237 it really needs to be 1 now.  This
   will be backported to Python 2.2.3 a well.  (SF #660455)
 
-- Added several bytecode optimizations.  Provides speed-ups to
-  inverted in/is tests, inverted jumps, while 1 loops, and jumps to
-  unconditional jumps.
-
-- Added a new opcode, NOP, which is used in some of the bytecode
-  transformations.
-
 - int(s, base) sometimes sign-folds hex and oct constants; it only
   does this when base is 0 and s.strip() starts with a '0'.  When the
   sign is actually folded, as in int("0xffffffff", 0) on a 32-bit
diff --git a/Python/ceval.c b/Python/ceval.c
index 7f8f654..3ea1bdc 100644
--- a/Python/ceval.c
+++ b/Python/ceval.c
@@ -873,9 +873,6 @@ eval_frame(PyFrameObject *f)
 
 		/* case STOP_CODE: this is an error! */
 
-		case NOP:
-			goto fast_next_opcode;
-
 		case LOAD_FAST:
 			x = GETLOCAL(oparg);
 			if (x != NULL) {
diff --git a/Python/compile.c b/Python/compile.c
index 4afd0eb..57f0edb 100644
--- a/Python/compile.c
+++ b/Python/compile.c
@@ -328,43 +328,6 @@ intern_strings(PyObject *tuple)
 #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])
-
-static unsigned int *
-markblocks(unsigned char *code, int len)
-{
-	unsigned int *blocks = PyMem_Malloc(len*sizeof(int));
-	int i,j, opcode, oldblock, newblock, blockcnt = 0;
-
-	if (blocks == NULL)
-		return NULL;
-	memset(blocks, 0, len*sizeof(int));
-	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);
-				oldblock = blocks[j];
-				newblock = ++blockcnt;
-				for (; j<len ; j++) {
-					if (blocks[j] != (unsigned)oldblock)
-						break;
-					blocks[j] = newblock;
-				}
-			break;
-		}
-	}
-	return blocks;
-}
 
 static PyObject *
 optimize_code(PyObject *code, PyObject* consts)
@@ -372,24 +335,18 @@ optimize_code(PyObject *code, PyObject* consts)
 	int i, j, codelen;
 	int tgt, tgttgt, opcode;
 	unsigned char *codestr;
-	unsigned int *blocks;
 
 	/* Make a modifiable copy of the code string */
 	if (!PyString_Check(code))
 		goto exitUnchanged;
 	codelen = PyString_Size(code);
 	codestr = PyMem_Malloc(codelen);
-	if (codestr == NULL)
+	if (codestr == NULL) 
 		goto exitUnchanged;
 	codestr = memcpy(codestr, PyString_AS_STRING(code), codelen);
-	blocks = markblocks(codestr, codelen);
-	if (blocks == NULL) {
-		PyMem_Free(codestr);
-		goto exitUnchanged;
-	}
 	assert(PyTuple_Check(consts));
 
-	for (i=0 ; i<codelen ; i += CODESIZE(codestr[i])) {
+	for (i=0 ; i<codelen-7 ; i += HAS_ARG(codestr[i]) ? 3 : 1) {
 		opcode = codestr[i];
 		switch (opcode) {
 
@@ -406,8 +363,8 @@ optimize_code(PyObject *code, PyObject* consts)
 			SETARG(codestr, i, 4);
 			break;
 
-		/* Replace BUILD_SEQN 2 UNPACK_SEQN 2 with ROT2 JMP+2 NOP NOP.
-		   Replace BUILD_SEQN 3 UNPACK_SEQN 3 with ROT3 ROT2 JMP+1 NOP.
+		/* Replace BUILD_SEQN 2 UNPACK_SEQN 2 with ROT2 JMP+2.
+		   Replace BUILD_SEQN 3 UNPACK_SEQN 3 with ROT3 ROT2 JMP+1.
 		   Note, these opcodes occur together only in assignment
 		   statements.  Accordingly, the unpack opcode is never
 		   a jump target.  */
@@ -420,8 +377,8 @@ optimize_code(PyObject *code, PyObject* consts)
 				codestr[i] = ROT_TWO;
 				codestr[i+1] = JUMP_FORWARD;
 				SETARG(codestr, i+1, 2);
-				codestr[i+4] = NOP;
-				codestr[i+5] = NOP;
+				codestr[i+4] = DUP_TOP;	 /* Filler codes used as NOPs */
+				codestr[i+5] = POP_TOP;
 				continue;
 			} 
 			if (GETARG(codestr, i) == 3 && \
@@ -429,41 +386,11 @@ optimize_code(PyObject *code, PyObject* consts)
 				codestr[i] = ROT_THREE;
 				codestr[i+1] = ROT_TWO;
 				codestr[i+2] = JUMP_FORWARD;
-				SETARG(codestr, i+2, 1);
-				codestr[i+5] = NOP;
+				SETARG(codestr, i+2, 1);	
+				codestr[i+5] = DUP_TOP;
 			}
 			break;
 
-		/* Simplify inverted tests.
-		   Must verify that sequence is a basic block because the jump
-		   can itself be a jump target.  Also, must verify that *both*
-		   jump alternatives go to a POP_TOP.  Otherwise, the code will
-		   expect the stack value to have been inverted.  */
-		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;
-			codestr[i] = NOP;
-			codestr[i+1] = JUMP_IF_TRUE;
-			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 (codestr[i+3] != UNARY_NOT || j < 6 || \
-			    j > 9 || !ISBASICBLOCK(blocks,i,4))
-				continue;
-			SETARG(codestr, i, (j^1));
-			codestr[i+3] = NOP;
-			break;
-
 		/* Replace jumps to unconditional jumps */
 		case FOR_ITER:
 		case JUMP_FORWARD:
@@ -475,7 +402,7 @@ optimize_code(PyObject *code, PyObject* consts)
 		case SETUP_EXCEPT:
 		case SETUP_FINALLY:
 			tgt = GETJUMPTGT(codestr, i);
-			if (!UNCONDITIONAL_JUMP(codestr[tgt]))
+			if (!UNCONDITIONAL_JUMP(codestr[tgt])) 
 				continue;
 			tgttgt = GETJUMPTGT(codestr, tgt);
 			if (opcode == JUMP_FORWARD) /* JMP_ABS can go backwards */
@@ -495,7 +422,6 @@ optimize_code(PyObject *code, PyObject* consts)
 	}
 	code = PyString_FromStringAndSize(codestr, codelen);
 	PyMem_Free(codestr);
-	PyMem_Free(blocks);
 	return code;
 
 exitUnchanged:
-- 
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