https://github.com/python/cpython/commit/6810928927e4d12d9a5dd90e672afb096882b730
commit: 6810928927e4d12d9a5dd90e672afb096882b730
branch: main
author: Brandt Bucher <[email protected]>
committer: brandtbucher <[email protected]>
date: 2024-10-02T19:24:37Z
summary:
GH-118093: Don't lose confidence when tracing through 100% biased branches
(GH-124813)
files:
A
Misc/NEWS.d/next/Core_and_Builtins/2024-09-30-16-39-37.gh-issue-118093.J2A3gz.rst
M Python/optimizer.c
diff --git
a/Misc/NEWS.d/next/Core_and_Builtins/2024-09-30-16-39-37.gh-issue-118093.J2A3gz.rst
b/Misc/NEWS.d/next/Core_and_Builtins/2024-09-30-16-39-37.gh-issue-118093.J2A3gz.rst
new file mode 100644
index 00000000000000..2e5c64581b6aef
--- /dev/null
+++
b/Misc/NEWS.d/next/Core_and_Builtins/2024-09-30-16-39-37.gh-issue-118093.J2A3gz.rst
@@ -0,0 +1,2 @@
+Improve the experimental JIT compiler's ability to stay "on trace" when
+encountering highly-biased branches.
diff --git a/Python/optimizer.c b/Python/optimizer.c
index 978649faa04d45..b876b6c2bd72fd 100644
--- a/Python/optimizer.c
+++ b/Python/optimizer.c
@@ -643,14 +643,12 @@ translate_bytecode_to_trace(
int bitcount = _Py_popcount32(counter);
int jump_likely = bitcount > 8;
/* If bitcount is 8 (half the jumps were taken), adjust
confidence by 50%.
- If it's 16 or 0 (all or none were taken), adjust by 10%
- (since the future is still somewhat uncertain).
For values in between, adjust proportionally. */
if (jump_likely) {
- confidence = confidence * (bitcount + 2) / 20;
+ confidence = confidence * bitcount / 16;
}
else {
- confidence = confidence * (18 - bitcount) / 20;
+ confidence = confidence * (16 - bitcount) / 16;
}
uint32_t uopcode = BRANCH_TO_GUARD[opcode -
POP_JUMP_IF_FALSE][jump_likely];
DPRINTF(2, "%d: %s(%d): counter=%04x, bitcount=%d, likely=%d,
confidence=%d, uopcode=%s\n",
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