Mercurial > cpython-lru_cache-weakref

diff Python/ceval.c @ 28302:8c082936daaf legacy-trunk

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Introduced macros for a simple opcode prediction protocol. Applied to common cases: COMPARE_OP is often followed by a JUMP_IF. JUMP_IF is usually followed by POP_TOP. Shows improved timings on PyStone, PyBench, and specific tests using timeit.py: python timeit.py -s "x=1" "if x==1: pass" python timeit.py -s "x=1" "if x==2: pass" python timeit.py -s "x=1" "if x: pass" python timeit.py -s "x=100" "while x!=1: x-=1" Potential future candidates: GET_ITER predicts FOR_ITER FOR_ITER predicts STORE_FAST or UNPACK_SEQUENCE Also, applied missing goto fast_next_opcode to DUP_TOPX.
author Raymond Hettinger <python@rcn.com>
date Sun, 16 Mar 2003 03:11:04 +0000
parents 7654c24decc4
children 470504ef578b
line wrap: on
line diff
--- a/Python/ceval.c	Sat Mar 15 12:25:00 2003 +0000
+++ b/Python/ceval.c	Sun Mar 16 03:11:04 2003 +0000
@@ -602,6 +602,26 @@
 #define JUMPTO(x)	(next_instr = first_instr + (x))
 #define JUMPBY(x)	(next_instr += (x))
 
+/* OpCode prediction macros
+	Some opcodes tend to come in pairs thus making it possible to predict
+	the second code when the first is run.  For example, COMPARE_OP is often
+	followed by JUMP_IF_FALSE or JUMP_IF_TRUE.  And, those opcodes are often
+	followed by a POP_TOP.
+
+	Verifying the prediction costs a single high-speed test of register
+	variable against a constant.  If the pairing was good, then the odds
+	processor has a high likelihood of making its own successful branch
+	prediction which results in a nearly zero overhead transition to the
+	next opcode.
+
+	A successful prediction saves a trip through the eval-loop including
+	its two unpredictable branches, the HASARG test and the switch-case.
+*/
+
+#define PREDICT(op)	if (*next_instr == op) goto PRED_##op
+#define PREDICTED(op)		PRED_##op: next_instr++
+#define PREDICTED_WITH_ARG(op)	PRED_##op: oparg = (next_instr += 3, (next_instr[-1]<<8) + next_instr[-2])
+
 /* Stack manipulation macros */
 
 #define STACK_LEVEL()	(stack_pointer - f->f_valuestack)
@@ -873,6 +893,7 @@
 			SETLOCAL(oparg, v);
 			goto fast_next_opcode;
 
+		PREDICTED(POP_TOP);
 		case POP_TOP:
 			v = POP();
 			Py_DECREF(v);
@@ -920,7 +941,7 @@
 				STACKADJ(2);
 				SET_TOP(x);
 				SET_SECOND(w);
-				continue;
+				goto fast_next_opcode;
 			} else if (oparg == 3) {
 				x = TOP();
 				Py_INCREF(x);
@@ -932,7 +953,7 @@
 				SET_TOP(x);
 				SET_SECOND(w);
 				SET_THIRD(v);
-				continue;
+				goto fast_next_opcode;
 			}
 			Py_FatalError("invalid argument to DUP_TOPX"
 				      " (bytecode corruption?)");
@@ -1918,8 +1939,10 @@
 			Py_DECREF(v);
 			Py_DECREF(w);
 			SET_TOP(x);
-			if (x != NULL) continue;
-			break;
+			if (x == NULL) break;
+			PREDICT(JUMP_IF_FALSE);
+			PREDICT(JUMP_IF_TRUE);
+			continue;
 
 		case IMPORT_NAME:
 			w = GETITEM(names, oparg);
@@ -1974,10 +1997,13 @@
 			JUMPBY(oparg);
 			goto fast_next_opcode;
 
+		PREDICTED_WITH_ARG(JUMP_IF_FALSE);
 		case JUMP_IF_FALSE:
 			w = TOP();
-			if (w == Py_True)
+			if (w == Py_True) {
+				PREDICT(POP_TOP);
 				goto fast_next_opcode;
+			}
 			if (w == Py_False) {
 				JUMPBY(oparg);
 				goto fast_next_opcode;
@@ -1991,10 +2017,13 @@
 				break;
 			continue;
 
+		PREDICTED_WITH_ARG(JUMP_IF_TRUE);
 		case JUMP_IF_TRUE:
 			w = TOP();
-			if (w == Py_False)
+			if (w == Py_False) {
+				PREDICT(POP_TOP);
 				goto fast_next_opcode;
+			}
 			if (w == Py_True) {
 				JUMPBY(oparg);
 				goto fast_next_opcode;