[Python-checkins] GH-91719: Make MSVC generate somewhat faster switch code (#91718)
gvanrossum
webhook-mailer at python.org
Thu Apr 21 14:54:12 EDT 2022
https://github.com/python/cpython/commit/f8dc6186d1857a19edd182277a9d78e6d6cc3787
commit: f8dc6186d1857a19edd182277a9d78e6d6cc3787
branch: main
author: Guido van Rossum <guido at python.org>
committer: gvanrossum <gvanrossum at gmail.com>
date: 2022-04-21T11:53:57-07:00
summary:
GH-91719: Make MSVC generate somewhat faster switch code (#91718)
Apparently a switch on an 8-bit quantity where all cases are
present generates a more efficient jump (doing only one indexed
memory load instead of two).
So we make opcode and use_tracing uint8_t, and generate a macro
full of extra `case NNN:` lines for all unused opcodes.
See https://github.com/faster-cpython/ideas/issues/321#issuecomment-1103263673
files:
M Include/cpython/pystate.h
M Include/opcode.h
M Python/ceval.c
M Tools/scripts/generate_opcode_h.py
diff --git a/Include/cpython/pystate.h b/Include/cpython/pystate.h
index 1af21a2c947d9..2bd46067cbbe1 100644
--- a/Include/cpython/pystate.h
+++ b/Include/cpython/pystate.h
@@ -46,7 +46,7 @@ typedef struct _PyCFrame {
* discipline and make sure that instances of this struct cannot
* accessed outside of their lifetime.
*/
- int use_tracing;
+ uint8_t use_tracing; // 0 or 255 (or'ed into opcode, hence 8-bit type)
/* Pointer to the currently executing frame (it can be NULL) */
struct _PyInterpreterFrame *current_frame;
struct _PyCFrame *previous;
diff --git a/Include/opcode.h b/Include/opcode.h
index 8db42380cedd1..89f56e27ed437 100644
--- a/Include/opcode.h
+++ b/Include/opcode.h
@@ -707,6 +707,84 @@ static const char *const _PyOpcode_OpName[256] = {
};
#endif
+#define EXTRA_CASES \
+ case 180: \
+ case 181: \
+ case 182: \
+ case 183: \
+ case 184: \
+ case 185: \
+ case 186: \
+ case 187: \
+ case 188: \
+ case 189: \
+ case 190: \
+ case 191: \
+ case 192: \
+ case 193: \
+ case 194: \
+ case 195: \
+ case 196: \
+ case 197: \
+ case 198: \
+ case 199: \
+ case 200: \
+ case 201: \
+ case 202: \
+ case 203: \
+ case 204: \
+ case 205: \
+ case 206: \
+ case 207: \
+ case 208: \
+ case 209: \
+ case 210: \
+ case 211: \
+ case 212: \
+ case 213: \
+ case 214: \
+ case 215: \
+ case 216: \
+ case 217: \
+ case 218: \
+ case 219: \
+ case 220: \
+ case 221: \
+ case 222: \
+ case 223: \
+ case 224: \
+ case 225: \
+ case 226: \
+ case 227: \
+ case 228: \
+ case 229: \
+ case 230: \
+ case 231: \
+ case 232: \
+ case 233: \
+ case 234: \
+ case 235: \
+ case 236: \
+ case 237: \
+ case 238: \
+ case 239: \
+ case 240: \
+ case 241: \
+ case 242: \
+ case 243: \
+ case 244: \
+ case 245: \
+ case 246: \
+ case 247: \
+ case 248: \
+ case 249: \
+ case 250: \
+ case 251: \
+ case 252: \
+ case 253: \
+ case 254: \
+ ;
+
#define HAS_ARG(op) ((op) >= HAVE_ARGUMENT)
/* Reserve some bytecodes for internal use in the compiler.
diff --git a/Python/ceval.c b/Python/ceval.c
index 12b0aef774e36..a80583f5abd12 100644
--- a/Python/ceval.c
+++ b/Python/ceval.c
@@ -1662,7 +1662,9 @@ _PyEval_EvalFrameDefault(PyThreadState *tstate, _PyInterpreterFrame *frame, int
#ifdef Py_STATS
int lastopcode = 0;
#endif
- int opcode; /* Current opcode */
+ // opcode is an 8-bit value to improve the code generated by MSVC
+ // for the big switch below (in combination with the EXTRA_CASES macro).
+ uint8_t opcode; /* Current opcode */
int oparg; /* Current opcode argument, if any */
_Py_atomic_int * const eval_breaker = &tstate->interp->ceval.eval_breaker;
@@ -5645,7 +5647,7 @@ _PyEval_EvalFrameDefault(PyThreadState *tstate, _PyInterpreterFrame *frame, int
#if USE_COMPUTED_GOTOS
_unknown_opcode:
#else
- default:
+ EXTRA_CASES // From opcode.h, a 'case' for each unused opcode
#endif
fprintf(stderr, "XXX lineno: %d, opcode: %d\n",
_PyInterpreterFrame_GetLine(frame), opcode);
diff --git a/Tools/scripts/generate_opcode_h.py b/Tools/scripts/generate_opcode_h.py
index a13fa778db4ea..1b45020835dd4 100644
--- a/Tools/scripts/generate_opcode_h.py
+++ b/Tools/scripts/generate_opcode_h.py
@@ -129,6 +129,13 @@ def main(opcode_py, outfile='Include/opcode.h'):
fobj.write("};\n")
fobj.write("#endif\n")
+ fobj.write("\n")
+ fobj.write("#define EXTRA_CASES \\\n")
+ for i, flag in enumerate(used):
+ if not flag:
+ fobj.write(f" case {i}: \\\n")
+ fobj.write(" ;\n")
+
fobj.write(footer)
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