[llvm] [BOLT][AArch64] Refuse to run CDSplit pass (PR #159351)
Paschalis Mpeis via llvm-commits
llvm-commits at lists.llvm.org
Wed Oct 1 04:24:12 PDT 2025
https://github.com/paschalis-mpeis updated https://github.com/llvm/llvm-project/pull/159351
>From 9f1fb0718fc400458d639dc26e204d35a8a3b43e Mon Sep 17 00:00:00 2001
From: Paschalis Mpeis <paschalis.mpeis at arm.com>
Date: Wed, 17 Sep 2025 11:34:59 +0100
Subject: [PATCH 1/4] [BOLT][AArch64] Refuse to run CDSplit pass
LongJmp does not support warm blocks. On builds without assertions, this
may lead to unexpected crashes.
This patch exits with a clear message.
---
bolt/include/bolt/Passes/SplitFunctions.h | 19 ------------
bolt/include/bolt/Utils/CommandLineOpts.h | 20 +++++++++++++
bolt/lib/Passes/LongJmp.cpp | 4 +++
bolt/lib/Passes/SplitFunctions.cpp | 36 +++++------------------
bolt/lib/Utils/CommandLineOpts.cpp | 23 +++++++++++++++
bolt/test/AArch64/unsupported-passes.test | 8 +++--
6 files changed, 60 insertions(+), 50 deletions(-)
diff --git a/bolt/include/bolt/Passes/SplitFunctions.h b/bolt/include/bolt/Passes/SplitFunctions.h
index 8bdc48b68eb7a..2c1bf1890cd97 100644
--- a/bolt/include/bolt/Passes/SplitFunctions.h
+++ b/bolt/include/bolt/Passes/SplitFunctions.h
@@ -18,25 +18,6 @@
namespace llvm {
namespace bolt {
-/// Strategy used to partition blocks into fragments.
-enum SplitFunctionsStrategy : char {
- /// Split each function into a hot and cold fragment using profiling
- /// information.
- Profile2 = 0,
- /// Split each function into a hot, warm, and cold fragment using
- /// profiling information.
- CDSplit,
- /// Split each function into a hot and cold fragment at a randomly chosen
- /// split point (ignoring any available profiling information).
- Random2,
- /// Split each function into N fragments at a randomly chosen split points
- /// (ignoring any available profiling information).
- RandomN,
- /// Split all basic blocks of each function into fragments such that each
- /// fragment contains exactly a single basic block.
- All
-};
-
class SplitStrategy {
public:
using BlockIt = BinaryFunction::BasicBlockOrderType::iterator;
diff --git a/bolt/include/bolt/Utils/CommandLineOpts.h b/bolt/include/bolt/Utils/CommandLineOpts.h
index 859d6f3bf6774..0964c2c9d8473 100644
--- a/bolt/include/bolt/Utils/CommandLineOpts.h
+++ b/bolt/include/bolt/Utils/CommandLineOpts.h
@@ -29,6 +29,25 @@ enum HeatmapModeKind {
HM_Optional // perf2bolt --heatmap
};
+/// Strategy used to partition blocks into fragments.
+enum SplitFunctionsStrategy : char {
+ /// Split each function into a hot and cold fragment using profiling
+ /// information.
+ Profile2 = 0,
+ /// Split each function into a hot, warm, and cold fragment using
+ /// profiling information.
+ CDSplit,
+ /// Split each function into a hot and cold fragment at a randomly chosen
+ /// split point (ignoring any available profiling information).
+ Random2,
+ /// Split each function into N fragments at a randomly chosen split points
+ /// (ignoring any available profiling information).
+ RandomN,
+ /// Split all basic blocks of each function into fragments such that each
+ /// fragment contains exactly a single basic block.
+ All
+};
+
using HeatmapBlockSizes = std::vector<unsigned>;
struct HeatmapBlockSpecParser : public llvm::cl::parser<HeatmapBlockSizes> {
explicit HeatmapBlockSpecParser(llvm::cl::Option &O)
@@ -78,6 +97,7 @@ extern llvm::cl::opt<std::string> OutputFilename;
extern llvm::cl::opt<std::string> PerfData;
extern llvm::cl::opt<bool> PrintCacheMetrics;
extern llvm::cl::opt<bool> PrintSections;
+extern llvm::cl::opt<SplitFunctionsStrategy> SplitStrategy;
// The format to use with -o in aggregation mode (perf2bolt)
enum ProfileFormatKind { PF_Fdata, PF_YAML };
diff --git a/bolt/lib/Passes/LongJmp.cpp b/bolt/lib/Passes/LongJmp.cpp
index 4dade161cc232..e62cbe4e6d9d5 100644
--- a/bolt/lib/Passes/LongJmp.cpp
+++ b/bolt/lib/Passes/LongJmp.cpp
@@ -894,6 +894,10 @@ void LongJmpPass::relaxLocalBranches(BinaryFunction &BF) {
}
Error LongJmpPass::runOnFunctions(BinaryContext &BC) {
+ if (opts::SplitStrategy == opts::SplitFunctionsStrategy::CDSplit) {
+ BC.errs() << "BOLT-ERROR: CDSplit is not supported on AArch64\n";
+ exit(1);
+ }
if (opts::CompactCodeModel) {
BC.outs()
diff --git a/bolt/lib/Passes/SplitFunctions.cpp b/bolt/lib/Passes/SplitFunctions.cpp
index b21401e069bfa..37243c5f3c7a1 100644
--- a/bolt/lib/Passes/SplitFunctions.cpp
+++ b/bolt/lib/Passes/SplitFunctions.cpp
@@ -85,29 +85,7 @@ static cl::opt<unsigned> SplitThreshold(
"size is reduced. Note that on some architectures the size can "
"increase after splitting."),
cl::init(0), cl::Hidden, cl::cat(BoltOptCategory));
-
-static cl::opt<SplitFunctionsStrategy> SplitStrategy(
- "split-strategy", cl::init(SplitFunctionsStrategy::Profile2),
- cl::values(clEnumValN(SplitFunctionsStrategy::Profile2, "profile2",
- "split each function into a hot and cold fragment "
- "using profiling information")),
- cl::values(clEnumValN(SplitFunctionsStrategy::CDSplit, "cdsplit",
- "split each function into a hot, warm, and cold "
- "fragment using profiling information")),
- cl::values(clEnumValN(
- SplitFunctionsStrategy::Random2, "random2",
- "split each function into a hot and cold fragment at a randomly chosen "
- "split point (ignoring any available profiling information)")),
- cl::values(clEnumValN(
- SplitFunctionsStrategy::RandomN, "randomN",
- "split each function into N fragments at a randomly chosen split "
- "points (ignoring any available profiling information)")),
- cl::values(clEnumValN(
- SplitFunctionsStrategy::All, "all",
- "split all basic blocks of each function into fragments such that each "
- "fragment contains exactly a single basic block")),
- cl::desc("strategy used to partition blocks into fragments"),
- cl::cat(BoltOptCategory));
+
static cl::opt<double> CallScale(
"call-scale",
@@ -724,14 +702,14 @@ Error SplitFunctions::runOnFunctions(BinaryContext &BC) {
// If split strategy is not CDSplit, then a second run of the pass is not
// needed after function reordering.
if (BC.HasFinalizedFunctionOrder &&
- opts::SplitStrategy != SplitFunctionsStrategy::CDSplit)
+ opts::SplitStrategy != opts::SplitFunctionsStrategy::CDSplit)
return Error::success();
std::unique_ptr<SplitStrategy> Strategy;
bool ForceSequential = false;
switch (opts::SplitStrategy) {
- case SplitFunctionsStrategy::CDSplit:
+ case opts::SplitFunctionsStrategy::CDSplit:
// CDSplit runs two splitting passes: hot-cold splitting (SplitPrfoile2)
// before function reordering and hot-warm-cold splitting
// (SplitCacheDirected) after function reordering.
@@ -742,21 +720,21 @@ Error SplitFunctions::runOnFunctions(BinaryContext &BC) {
opts::AggressiveSplitting = true;
BC.HasWarmSection = true;
break;
- case SplitFunctionsStrategy::Profile2:
+ case opts::SplitFunctionsStrategy::Profile2:
Strategy = std::make_unique<SplitProfile2>();
break;
- case SplitFunctionsStrategy::Random2:
+ case opts::SplitFunctionsStrategy::Random2:
Strategy = std::make_unique<SplitRandom2>();
// If we split functions randomly, we need to ensure that across runs with
// the same input, we generate random numbers for each function in the same
// order.
ForceSequential = true;
break;
- case SplitFunctionsStrategy::RandomN:
+ case opts::SplitFunctionsStrategy::RandomN:
Strategy = std::make_unique<SplitRandomN>();
ForceSequential = true;
break;
- case SplitFunctionsStrategy::All:
+ case opts::SplitFunctionsStrategy::All:
Strategy = std::make_unique<SplitAll>();
break;
}
diff --git a/bolt/lib/Utils/CommandLineOpts.cpp b/bolt/lib/Utils/CommandLineOpts.cpp
index 5635da476451d..095612ac3a4ac 100644
--- a/bolt/lib/Utils/CommandLineOpts.cpp
+++ b/bolt/lib/Utils/CommandLineOpts.cpp
@@ -104,6 +104,29 @@ ExecutionCountThreshold("execution-count-threshold",
cl::Hidden,
cl::cat(BoltOptCategory));
+cl::opt<SplitFunctionsStrategy> SplitStrategy(
+ "split-strategy", cl::init(SplitFunctionsStrategy::Profile2),
+ cl::values(clEnumValN(SplitFunctionsStrategy::Profile2, "profile2",
+ "split each function into a hot and cold fragment "
+ "using profiling information")),
+ cl::values(clEnumValN(SplitFunctionsStrategy::CDSplit, "cdsplit",
+ "split each function into a hot, warm, and cold "
+ "fragment using profiling information")),
+ cl::values(clEnumValN(
+ SplitFunctionsStrategy::Random2, "random2",
+ "split each function into a hot and cold fragment at a randomly chosen "
+ "split point (ignoring any available profiling information)")),
+ cl::values(clEnumValN(
+ SplitFunctionsStrategy::RandomN, "randomN",
+ "split each function into N fragments at a randomly chosen split "
+ "points (ignoring any available profiling information)")),
+ cl::values(clEnumValN(
+ SplitFunctionsStrategy::All, "all",
+ "split all basic blocks of each function into fragments such that each "
+ "fragment contains exactly a single basic block")),
+ cl::desc("strategy used to partition blocks into fragments"),
+ cl::cat(BoltOptCategory));
+
bool HeatmapBlockSpecParser::parse(cl::Option &O, StringRef ArgName,
StringRef Arg, HeatmapBlockSizes &Val) {
// Parses a human-readable suffix into a shift amount or nullopt on error.
diff --git a/bolt/test/AArch64/unsupported-passes.test b/bolt/test/AArch64/unsupported-passes.test
index 886fc1c574dcf..f70c4d42e2929 100644
--- a/bolt/test/AArch64/unsupported-passes.test
+++ b/bolt/test/AArch64/unsupported-passes.test
@@ -3,6 +3,10 @@
// REQUIRES: system-linux,asserts,target=aarch64{{.*}}
RUN: %clang %cflags %p/../Inputs/hello.c -o %t -Wl,-q
-RUN: not llvm-bolt %t -o %t.bolt --frame-opt=all 2>&1 | FileCheck %s
+RUN: not llvm-bolt %t -o %t.bolt --frame-opt=all 2>&1 | FileCheck %s --check-prefix=CHECK-FRAME-OPT
-CHECK: BOLT-ERROR: frame-optimizer is supported only on X86
+CHECK-FRAME-OPT: BOLT-ERROR: frame-optimizer is supported only on X86
+
+RUN: not llvm-bolt %t -o %t.bolt split-functions --split-strategy=cdsplit 2>&1 | FileCheck %s --check-prefix=CHECK-CDSPLIT
+
+CHECK-CDSPLIT: BOLT-ERROR: CDSplit is not supported on AArch64
>From 1a1405f432577f67063524f7e58a2c681919ba7f Mon Sep 17 00:00:00 2001
From: Paschalis Mpeis <paschalis.mpeis at arm.com>
Date: Wed, 17 Sep 2025 13:55:20 +0100
Subject: [PATCH 2/4] code formatter fix
---
bolt/lib/Passes/SplitFunctions.cpp | 1 -
1 file changed, 1 deletion(-)
diff --git a/bolt/lib/Passes/SplitFunctions.cpp b/bolt/lib/Passes/SplitFunctions.cpp
index 37243c5f3c7a1..eab669b32b71e 100644
--- a/bolt/lib/Passes/SplitFunctions.cpp
+++ b/bolt/lib/Passes/SplitFunctions.cpp
@@ -85,7 +85,6 @@ static cl::opt<unsigned> SplitThreshold(
"size is reduced. Note that on some architectures the size can "
"increase after splitting."),
cl::init(0), cl::Hidden, cl::cat(BoltOptCategory));
-
static cl::opt<double> CallScale(
"call-scale",
>From 2d8293101f1f7e940e95abcf01d8256ce2fe661f Mon Sep 17 00:00:00 2001
From: Paschalis Mpeis <paschalis.mpeis at arm.com>
Date: Mon, 29 Sep 2025 13:46:03 +0100
Subject: [PATCH 3/4] Addressing reviewers
---
bolt/lib/Passes/LongJmp.cpp | 7 +++++--
bolt/test/AArch64/unsupported-passes.test | 3 +--
2 files changed, 6 insertions(+), 4 deletions(-)
diff --git a/bolt/lib/Passes/LongJmp.cpp b/bolt/lib/Passes/LongJmp.cpp
index e62cbe4e6d9d5..03fc10709f48d 100644
--- a/bolt/lib/Passes/LongJmp.cpp
+++ b/bolt/lib/Passes/LongJmp.cpp
@@ -894,8 +894,11 @@ void LongJmpPass::relaxLocalBranches(BinaryFunction &BF) {
}
Error LongJmpPass::runOnFunctions(BinaryContext &BC) {
- if (opts::SplitStrategy == opts::SplitFunctionsStrategy::CDSplit) {
- BC.errs() << "BOLT-ERROR: CDSplit is not supported on AArch64\n";
+
+ if (!opts::CompactCodeModel &&
+ opts::SplitStrategy == opts::SplitFunctionsStrategy::CDSplit) {
+ BC.errs() << "BOLT-ERROR: CDSplit is not supported with LongJmp. Try with "
+ "'--compact-code-model'\n";
exit(1);
}
diff --git a/bolt/test/AArch64/unsupported-passes.test b/bolt/test/AArch64/unsupported-passes.test
index f70c4d42e2929..5b12d86500eea 100644
--- a/bolt/test/AArch64/unsupported-passes.test
+++ b/bolt/test/AArch64/unsupported-passes.test
@@ -8,5 +8,4 @@ RUN: not llvm-bolt %t -o %t.bolt --frame-opt=all 2>&1 | FileCheck %s --check-pre
CHECK-FRAME-OPT: BOLT-ERROR: frame-optimizer is supported only on X86
RUN: not llvm-bolt %t -o %t.bolt split-functions --split-strategy=cdsplit 2>&1 | FileCheck %s --check-prefix=CHECK-CDSPLIT
-
-CHECK-CDSPLIT: BOLT-ERROR: CDSplit is not supported on AArch64
+CHECK-CDSPLIT: BOLT-ERROR: CDSplit is not supported with LongJmp. Try with '--compact-code-model'
>From cc477f0527475495a27cf3995179f1af6d33bdf5 Mon Sep 17 00:00:00 2001
From: Paschalis Mpeis <paschalis.mpeis at arm.com>
Date: Wed, 1 Oct 2025 12:22:10 +0100
Subject: [PATCH 4/4] Addressing reviewers (2)
---
bolt/lib/Passes/LongJmp.cpp | 9 +++------
bolt/lib/Rewrite/RewriteInstance.cpp | 7 +++++++
2 files changed, 10 insertions(+), 6 deletions(-)
diff --git a/bolt/lib/Passes/LongJmp.cpp b/bolt/lib/Passes/LongJmp.cpp
index 03fc10709f48d..03c1ea9d837e2 100644
--- a/bolt/lib/Passes/LongJmp.cpp
+++ b/bolt/lib/Passes/LongJmp.cpp
@@ -895,12 +895,9 @@ void LongJmpPass::relaxLocalBranches(BinaryFunction &BF) {
Error LongJmpPass::runOnFunctions(BinaryContext &BC) {
- if (!opts::CompactCodeModel &&
- opts::SplitStrategy == opts::SplitFunctionsStrategy::CDSplit) {
- BC.errs() << "BOLT-ERROR: CDSplit is not supported with LongJmp. Try with "
- "'--compact-code-model'\n";
- exit(1);
- }
+ assert((opts::CompactCodeModel ||
+ opts::SplitStrategy != opts::SplitFunctionsStrategy::CDSplit) &&
+ "LongJmp cannot work with functions split in more than two fragments");
if (opts::CompactCodeModel) {
BC.outs()
diff --git a/bolt/lib/Rewrite/RewriteInstance.cpp b/bolt/lib/Rewrite/RewriteInstance.cpp
index a6e4dbc9c192f..db5628ecd400c 100644
--- a/bolt/lib/Rewrite/RewriteInstance.cpp
+++ b/bolt/lib/Rewrite/RewriteInstance.cpp
@@ -2113,6 +2113,13 @@ void RewriteInstance::adjustCommandLineOptions() {
opts::SplitEH = false;
}
+ if (BC->isAArch64() && !opts::CompactCodeModel &&
+ opts::SplitStrategy == opts::SplitFunctionsStrategy::CDSplit) {
+ BC->errs() << "BOLT-ERROR: CDSplit is not supported with LongJmp. Try with "
+ "'--compact-code-model'\n";
+ exit(1);
+ }
+
if (opts::StrictMode && !BC->HasRelocations) {
BC->errs()
<< "BOLT-WARNING: disabling strict mode (-strict) in non-relocation "
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