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gh-109039: Branch prediction for Tier 2 interpreter (#109038)

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This adds a 16-bit inline cache entry to the conditional branch instructions POP_JUMP_IF_{FALSE,TRUE,NONE,NOT_NONE} and their instrumented variants, which is used to keep track of the branch direction.

Each time we encounter these instructions we shift the cache entry left by one and set the bottom bit to whether we jumped.

Then when it's time to translate such a branch to Tier 2 uops, we use the bit count from the cache entry to decided whether to continue translating the "didn't jump" branch or the "jumped" branch.

The counter is initialized to a pattern of alternating ones and zeros to avoid bias.

The .pyc file magic number is updated. There's a new test, some fixes for existing tests, and a few miscellaneous cleanups.
This commit is contained in:
Guido van Rossum 2023-09-11 11:20:24 -07:00 • committed by GitHub
parent ecd21a629a
commit bcce5e2718
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GPG key ID: 4AEE18F83AFDEB23
15 changed files with 339 additions and 181 deletions
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58
Python/generated_cases.c.h generated
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@ -2996,8 +2996,13 @@
PyObject *cond;
cond = stack_pointer[-1];
assert(PyBool_Check(cond));
JUMPBY(oparg * Py_IsFalse(cond));
int flag = Py_IsFalse(cond);
#if ENABLE_SPECIALIZATION
next_instr->cache = (next_instr->cache << 1) | flag;
#endif
JUMPBY(oparg * flag);
STACK_SHRINK(1);
next_instr += 1;
DISPATCH();
}
@ -3005,8 +3010,13 @@
PyObject *cond;
cond = stack_pointer[-1];
assert(PyBool_Check(cond));
JUMPBY(oparg * Py_IsTrue(cond));
int flag = Py_IsTrue(cond);
#if ENABLE_SPECIALIZATION
next_instr->cache = (next_instr->cache << 1) | flag;
#endif
JUMPBY(oparg * flag);
STACK_SHRINK(1);
next_instr += 1;
DISPATCH();
}
@ -3029,9 +3039,14 @@
cond = b;
{
assert(PyBool_Check(cond));
JUMPBY(oparg * Py_IsTrue(cond));
int flag = Py_IsTrue(cond);
#if ENABLE_SPECIALIZATION
next_instr->cache = (next_instr->cache << 1) | flag;
#endif
JUMPBY(oparg * flag);
}
STACK_SHRINK(1);
next_instr += 1;
DISPATCH();
}
@ -3054,9 +3069,14 @@
cond = b;
{
assert(PyBool_Check(cond));
JUMPBY(oparg * Py_IsFalse(cond));
int flag = Py_IsFalse(cond);
#if ENABLE_SPECIALIZATION
next_instr->cache = (next_instr->cache << 1) | flag;
#endif
JUMPBY(oparg * flag);
}
STACK_SHRINK(1);
next_instr += 1;
DISPATCH();
}
@ -4921,8 +4941,13 @@
PyObject *cond = POP();
assert(PyBool_Check(cond));
_Py_CODEUNIT *here = next_instr - 1;
int offset = Py_IsTrue(cond) * oparg;
int flag = Py_IsTrue(cond);
int offset = flag * oparg;
#if ENABLE_SPECIALIZATION
next_instr->cache = (next_instr->cache << 1) | flag;
#endif
INSTRUMENTED_JUMP(here, next_instr + offset, PY_MONITORING_EVENT_BRANCH);
next_instr += 1;
DISPATCH();
}
@ -4930,23 +4955,33 @@
PyObject *cond = POP();
assert(PyBool_Check(cond));
_Py_CODEUNIT *here = next_instr - 1;
int offset = Py_IsFalse(cond) * oparg;
int flag = Py_IsFalse(cond);
int offset = flag * oparg;
#if ENABLE_SPECIALIZATION
next_instr->cache = (next_instr->cache << 1) | flag;
#endif
INSTRUMENTED_JUMP(here, next_instr + offset, PY_MONITORING_EVENT_BRANCH);
next_instr += 1;
DISPATCH();
}
TARGET(INSTRUMENTED_POP_JUMP_IF_NONE) {
PyObject *value = POP();
_Py_CODEUNIT *here = next_instr-1;
_Py_CODEUNIT *here = next_instr - 1;
int flag = Py_IsNone(value);
int offset;
if (Py_IsNone(value)) {
if (flag) {
offset = oparg;
}
else {
Py_DECREF(value);
offset = 0;
}
#if ENABLE_SPECIALIZATION
next_instr->cache = (next_instr->cache << 1) | flag;
#endif
INSTRUMENTED_JUMP(here, next_instr + offset, PY_MONITORING_EVENT_BRANCH);
next_instr += 1;
DISPATCH();
}
@ -4954,14 +4989,19 @@
PyObject *value = POP();
_Py_CODEUNIT *here = next_instr-1;
int offset;
if (Py_IsNone(value)) {
int nflag = Py_IsNone(value);
if (nflag) {
offset = 0;
}
else {
Py_DECREF(value);
offset = oparg;
}
#if ENABLE_SPECIALIZATION
next_instr->cache = (next_instr->cache << 1) | !nflag;
#endif
INSTRUMENTED_JUMP(here, next_instr + offset, PY_MONITORING_EVENT_BRANCH);
next_instr += 1;
DISPATCH();
}