From 6810928927e4d12d9a5dd90e672afb096882b730 Mon Sep 17 00:00:00 2001 From: Brandt Bucher Date: Wed, 2 Oct 2024 12:24:37 -0700 Subject: [PATCH] GH-118093: Don't lose confidence when tracing through 100% biased branches (GH-124813) --- .../2024-09-30-16-39-37.gh-issue-118093.J2A3gz.rst | 2 ++ Python/optimizer.c | 6 ++---- 2 files changed, 4 insertions(+), 4 deletions(-) create mode 100644 Misc/NEWS.d/next/Core_and_Builtins/2024-09-30-16-39-37.gh-issue-118093.J2A3gz.rst 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",