[llvm] [AArch64] Lower jump table cases threshold to 10 (PR #143632)
Guy David via llvm-commits
llvm-commits at lists.llvm.org
Tue Jun 10 16:47:02 PDT 2025
https://github.com/guy-david created https://github.com/llvm/llvm-project/pull/143632
Previous stabs at this setting (https://github.com/llvm/llvm-project/pull/71166) hypertuned it for SPEC2017, but Clang's own compilation can benefit from a slightly lower threshold, yielding a 0.3% improvement in compile time, while still not regressing SPEC.
Most notable benefactors of this change are:
- `llvm::Instruction::getNumSuccessors` (11 cases)
- `llvm::Instruction::getSuccessor` (11 cases)
Test Suite:
```
Tests: 4316
Metric: compile_time
Program compile_time
lhs rhs diff
SingleSour...ce/UnitTests/SignlessTypes/div 0.02 0.02 3.0%
SingleSour.../UnitTests/SignlessTypes/cast2 0.02 0.02 2.8%
SingleSource/Benchmarks/Misc/flops-4 0.02 0.02 1.9%
SingleSour...ebra/solvers/cholesky/cholesky 0.05 0.05 1.8%
SingleSour...tTests/2020-01-06-coverage-006 0.02 0.02 1.7%
SingleSour...ce/Benchmarks/Stanford/FloatMM 0.03 0.03 1.7%
SingleSour...9-04-16-BitfieldInitialization 0.02 0.02 1.7%
SingleSour...nitTests/2003-07-08-BitOpsTest 0.02 0.02 1.7%
MultiSourc...marks/Prolangs-C++/vcirc/vcirc 0.02 0.02 1.6%
MultiSourc...Prolangs-C/fixoutput/fixoutput 0.05 0.05 1.5%
SingleSour...h/stencils/jacobi-1d/jacobi-1d 0.04 0.04 1.4%
MultiSourc...rks/Prolangs-C++/office/office 0.28 0.28 1.4%
SingleSour...arks/Adobe-C++/functionobjects 0.39 0.40 1.3%
SingleSour...Tests/2003-10-29-ScalarReplBug 0.02 0.02 1.2%
SingleSour...arks/Adobe-C++/stepanov_vector 0.41 0.42 1.2%
Geomean difference -0.3%
compile_time
l/r lhs rhs diff
count 4316.000000 4316.000000 469.000000
mean 0.057747 0.057595 -0.003034
std 0.544528 0.543139 0.007625
min 0.000000 0.000000 -0.035294
25% 0.000000 0.000000 -0.007006
50% 0.000000 0.000000 -0.003257
75% 0.000000 0.000000 0.000000
max 18.295300 18.252500 0.030151
```
>From 925a6c7a36817f89d2b8435fd1c3f8849141e8f0 Mon Sep 17 00:00:00 2001
From: Guy David <guyda96 at gmail.com>
Date: Mon, 9 Jun 2025 14:05:06 +0300
Subject: [PATCH] [AArch64] Lower jump table cases threshold to 10
Previous stabs at this setting hypertuned it for SPEC2017, but Clang's
own compilation can benefit from a slightly lower threshold, yielding
0.3% improvement in compile time, while still maintaining a 0.1%
improvement in SPEC2017.
Most notable benefactors of this change are:
- llvm::Instruction::getNumSuccessors (11 cases)
- llvm::Instruction::getSuccessor (11 cases)
---
llvm/lib/Target/AArch64/AArch64Subtarget.cpp | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/llvm/lib/Target/AArch64/AArch64Subtarget.cpp b/llvm/lib/Target/AArch64/AArch64Subtarget.cpp
index a28e6bad0dca0..68ed10570a52f 100644
--- a/llvm/lib/Target/AArch64/AArch64Subtarget.cpp
+++ b/llvm/lib/Target/AArch64/AArch64Subtarget.cpp
@@ -73,7 +73,7 @@ static cl::opt<AArch64PAuth::AuthCheckMethod>
cl::values(AUTH_CHECK_METHOD_CL_VALUES_LR));
static cl::opt<unsigned> AArch64MinimumJumpTableEntries(
- "aarch64-min-jump-table-entries", cl::init(13), cl::Hidden,
+ "aarch64-min-jump-table-entries", cl::init(10), cl::Hidden,
cl::desc("Set minimum number of entries to use a jump table on AArch64"));
static cl::opt<unsigned> AArch64StreamingHazardSize(
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