[llvm] TableGen: Emit perfect hash function for runtime libcalls (PR #150192)
Matt Arsenault via llvm-commits
llvm-commits at lists.llvm.org
Thu Aug 14 07:46:32 PDT 2025
https://github.com/arsenm updated https://github.com/llvm/llvm-project/pull/150192
>From 904e7a4aaa59cf3274f83b093734fd8959ba2ee3 Mon Sep 17 00:00:00 2001
From: Matt Arsenault <Matthew.Arsenault at amd.com>
Date: Sat, 19 Jul 2025 18:39:12 +0900
Subject: [PATCH 1/6] TableGen: Emit perfect hash function for runtime libcalls
a96121089b9c94e08c6632f91f2dffc73c0ffa28 reverted a change
to use a binary search on the string name table because it
was too slow. This replaces it with a static string hash
table based on the known set of libcall names. Microbenchmarking
shows this is similarly fast to using DenseMap. It's possibly
slightly slower than using StringSet, though these aren't an
exact comparison. This also saves on the one time use construction
of the map, so it could be better in practice.
This search isn't simple set check, since it does find the
range of possible matches with the same name. There's also
an additional check for whether the current target supports
the name. The runtime constructed set doesn't require this,
since it only adds the symbols live for the target.
Followed algorithm from this post
http://0x80.pl/notesen/2023-04-30-lookup-in-strings.html
I'm also thinking the 2 special case global symbols should
just be added to RuntimeLibcalls. There are also other global
references emitted in the backend that aren't tracked; we probably
should just use this as a centralized database for all compiler
selected symbols.
---
llvm/benchmarks/CMakeLists.txt | 17 ++
llvm/benchmarks/RuntimeLibcalls.cpp | 116 ++++++++++
llvm/include/llvm/IR/RuntimeLibcalls.h | 44 +++-
llvm/lib/IR/RuntimeLibcalls.cpp | 58 ++---
llvm/lib/Object/IRSymtab.cpp | 46 ++--
llvm/test/TableGen/RuntimeLibcallEmitter.td | 26 +++
llvm/unittests/IR/CMakeLists.txt | 1 +
llvm/unittests/IR/RuntimeLibcallsTest.cpp | 63 ++++++
.../TableGen/Basic/RuntimeLibcallsEmitter.cpp | 203 +++++++++++++++++-
9 files changed, 493 insertions(+), 81 deletions(-)
create mode 100644 llvm/benchmarks/RuntimeLibcalls.cpp
create mode 100644 llvm/unittests/IR/RuntimeLibcallsTest.cpp
diff --git a/llvm/benchmarks/CMakeLists.txt b/llvm/benchmarks/CMakeLists.txt
index 1078efa55f497..9613678d2e0ac 100644
--- a/llvm/benchmarks/CMakeLists.txt
+++ b/llvm/benchmarks/CMakeLists.txt
@@ -11,3 +11,20 @@ add_benchmark(FormatVariadicBM FormatVariadicBM.cpp PARTIAL_SOURCES_INTENDED)
add_benchmark(GetIntrinsicInfoTableEntriesBM GetIntrinsicInfoTableEntriesBM.cpp PARTIAL_SOURCES_INTENDED)
add_benchmark(SandboxIRBench SandboxIRBench.cpp PARTIAL_SOURCES_INTENDED)
+# Extract the list of symbols in a random utility as sample data.
+set(SYMBOL_TEST_DATA_FILE "sample_symbol_list.txt")
+set(SYMBOL_TEST_DATA_SOURCE_BINARY $<TARGET_FILE:llc>)
+
+add_custom_command(OUTPUT ${SYMBOL_TEST_DATA_FILE}
+ COMMAND $<TARGET_FILE:llvm-nm> --no-demangle --no-sort
+ --format=just-symbols
+ ${SYMBOL_TEST_DATA_SOURCE_BINARY} > ${SYMBOL_TEST_DATA_FILE}
+ DEPENDS "$<TARGET_FILE:llvm-nm>" "$<TARGET_FILE:llc>")
+
+add_custom_target(generate-runtime-libcalls-sample-symbol-list
+ DEPENDS ${SYMBOL_TEST_DATA_FILE})
+add_benchmark(RuntimeLibcallsBench RuntimeLibcalls.cpp PARTIAL_SOURCES_INTENDED)
+
+add_dependencies(RuntimeLibcallsBench generate-runtime-libcalls-sample-symbol-list)
+target_compile_definitions(RuntimeLibcallsBench PRIVATE
+ -DSYMBOL_TEST_DATA_FILE="${CMAKE_CURRENT_BINARY_DIR}/${SYMBOL_TEST_DATA_FILE}")
diff --git a/llvm/benchmarks/RuntimeLibcalls.cpp b/llvm/benchmarks/RuntimeLibcalls.cpp
new file mode 100644
index 0000000000000..47f68abff1e0d
--- /dev/null
+++ b/llvm/benchmarks/RuntimeLibcalls.cpp
@@ -0,0 +1,116 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/IR/RuntimeLibcalls.h"
+#include "benchmark/benchmark.h"
+#include "llvm/IR/DataLayout.h"
+#include "llvm/Support/Error.h"
+#include "llvm/Support/LineIterator.h"
+#include "llvm/Support/MemoryBuffer.h"
+#include "llvm/TargetParser/Triple.h"
+#include <random>
+#include <string>
+using namespace llvm;
+
+static constexpr unsigned MaxFuncNameSize = 53;
+
+static std::vector<StringRef> getLibcallNameStringRefs() {
+ std::vector<StringRef> Names(RTLIB::NumLibcallImpls);
+ // Keep the strlens on the StringRef construction out of the benchmark loop.
+ for (RTLIB::LibcallImpl LC : RTLIB::libcall_impls()) {
+ const char *Name = RTLIB::RuntimeLibcallsInfo::getLibcallImplName(LC);
+ Names[LC] = StringRef(Name);
+ }
+
+ return Names;
+}
+
+static std::vector<std::string> getRandomFuncNames() {
+ std::mt19937_64 Rng;
+ std::uniform_int_distribution<> StringLengthDistribution(1, MaxFuncNameSize);
+ std::uniform_int_distribution<> CharDistribution(1, 255);
+ int NumTestFuncs = 1 << 10;
+ std::vector<std::string> TestFuncNames(NumTestFuncs);
+
+ for (std::string &TestFuncName : TestFuncNames) {
+ for (int I = 0, E = StringLengthDistribution(Rng); I != E; ++I)
+ TestFuncName += static_cast<char>(CharDistribution(Rng));
+ }
+
+ return TestFuncNames;
+}
+
+static std::vector<std::string> readSymbolsFromFile(StringRef InputFile) {
+ auto BufOrError = MemoryBuffer::getFileOrSTDIN(InputFile, /*IsText=*/true);
+ if (!BufOrError) {
+ reportFatalUsageError("failed to open \'" + Twine(InputFile) +
+ "\': " + BufOrError.getError().message());
+ }
+
+ // Hackily figure out if there's a prefix on the symbol names - llvm-nm
+ // appears to not have a flag to skip this.
+ llvm::Triple HostTriple(LLVM_HOST_TRIPLE);
+ std::string DummyDatalayout = "e";
+ DummyDatalayout += DataLayout::getManglingComponent(HostTriple);
+
+ DataLayout DL(DummyDatalayout);
+ char GlobalPrefix = DL.getGlobalPrefix();
+
+ std::vector<std::string> Lines;
+ for (line_iterator LineIt(**BufOrError, /*SkipBlanks=*/true);
+ !LineIt.is_at_eof(); ++LineIt) {
+ StringRef SymbolName = *LineIt;
+ SymbolName.consume_front(StringRef(&GlobalPrefix, 1));
+
+ Lines.push_back(SymbolName.str());
+ }
+ return Lines;
+}
+
+static void BM_LookupRuntimeLibcallByNameKnownCalls(benchmark::State &State) {
+ std::vector<StringRef> Names = getLibcallNameStringRefs();
+
+ for (auto _ : State) {
+ for (StringRef Name : Names) {
+ benchmark::DoNotOptimize(
+ RTLIB::RuntimeLibcallsInfo::lookupLibcallImplName(Name).empty());
+ }
+ }
+}
+
+static void BM_LookupRuntimeLibcallByNameRandomCalls(benchmark::State &State) {
+ std::vector<std::string> TestFuncNames = getRandomFuncNames();
+
+ for (auto _ : State) {
+ for (const std::string &Name : TestFuncNames) {
+ benchmark::DoNotOptimize(
+ RTLIB::RuntimeLibcallsInfo::lookupLibcallImplName(StringRef(Name))
+ .empty());
+ }
+ }
+}
+
+// This isn't fully representative, it doesn't include any anonymous functions.
+// nm -n --no-demangle --format=just-symbols sample-binary > sample.txt
+static void BM_LookupRuntimeLibcallByNameSampleData(benchmark::State &State) {
+ std::vector<std::string> TestFuncNames =
+ readSymbolsFromFile(SYMBOL_TEST_DATA_FILE);
+ for (auto _ : State) {
+ for (const std::string &Name : TestFuncNames) {
+ benchmark::DoNotOptimize(
+ RTLIB::RuntimeLibcallsInfo::lookupLibcallImplName(StringRef(Name))
+ .empty());
+ }
+ }
+}
+
+BENCHMARK(BM_LookupRuntimeLibcallByNameKnownCalls);
+BENCHMARK(BM_LookupRuntimeLibcallByNameRandomCalls);
+BENCHMARK(BM_LookupRuntimeLibcallByNameSampleData);
+
+BENCHMARK_MAIN();
diff --git a/llvm/include/llvm/IR/RuntimeLibcalls.h b/llvm/include/llvm/IR/RuntimeLibcalls.h
index 2d1d07c5fd81b..078098eeb7148 100644
--- a/llvm/include/llvm/IR/RuntimeLibcalls.h
+++ b/llvm/include/llvm/IR/RuntimeLibcalls.h
@@ -132,11 +132,41 @@ struct RuntimeLibcallsInfo {
return ImplToLibcall[Impl];
}
+ /// Check if a function name is a recognized runtime call of any kind. This
+ /// does not consider if this call is available for any current compilation,
+ /// just that it is a known call somewhere. This returns the set of all
+ /// LibcallImpls which match the name; multiple implementations with the same
+ /// name may exist but differ in interpretation based on the target context.
+ ///
+ /// Generated by tablegen.
+ LLVM_ABI static inline iota_range<RTLIB::LibcallImpl>
+ lookupLibcallImplName(StringRef Name){
+ // Inlining the early exit on the string name appears to be worthwhile when
+ // querying a real set of symbols
+#define GET_LOOKUP_LIBCALL_IMPL_NAME_BODY
+#include "llvm/IR/RuntimeLibcalls.inc"
+#undef GET_LOOKUP_LIBCALL_IMPL_NAME_BODY
+ }
+
/// Check if this is valid libcall for the current module, otherwise
/// RTLIB::Unsupported.
- LLVM_ABI RTLIB::LibcallImpl getSupportedLibcallImpl(StringRef FuncName) const;
+ LLVM_ABI RTLIB::LibcallImpl
+ getSupportedLibcallImpl(StringRef FuncName) const {
+ for (RTLIB::LibcallImpl Impl : lookupLibcallImplName(FuncName)) {
+ // FIXME: This should not depend on looking up ImplToLibcall, only the
+ // list of libcalls for the module.
+ RTLIB::LibcallImpl Recognized = LibcallImpls[ImplToLibcall[Impl]];
+ if (Recognized != RTLIB::Unsupported)
+ return Recognized;
+ }
+
+ return RTLIB::Unsupported;
+ }
private:
+ LLVM_ABI static iota_range<RTLIB::LibcallImpl>
+ lookupLibcallImplNameImpl(StringRef Name);
+
/// Stores the implementation choice for each each libcall.
RTLIB::LibcallImpl LibcallImpls[RTLIB::UNKNOWN_LIBCALL + 1] = {
RTLIB::Unsupported};
@@ -157,13 +187,11 @@ struct RuntimeLibcallsInfo {
/// Map from a concrete LibcallImpl implementation to its RTLIB::Libcall kind.
LLVM_ABI static const RTLIB::Libcall ImplToLibcall[RTLIB::NumLibcallImpls];
- /// Check if a function name is a recognized runtime call of any kind. This
- /// does not consider if this call is available for any current compilation,
- /// just that it is a known call somewhere. This returns the set of all
- /// LibcallImpls which match the name; multiple implementations with the same
- /// name may exist but differ in interpretation based on the target context.
- LLVM_ABI static iterator_range<ArrayRef<uint16_t>::const_iterator>
- getRecognizedLibcallImpls(StringRef FuncName);
+ /// Utility function for tablegenerated lookup function. Return a range of
+ /// enum values that apply for the function name at \p NameOffsetEntry with
+ /// the value \p StrOffset.
+ static inline iota_range<RTLIB::LibcallImpl>
+ libcallImplNameHit(uint16_t NameOffsetEntry, uint16_t StrOffset);
static bool darwinHasSinCosStret(const Triple &TT) {
if (!TT.isOSDarwin())
diff --git a/llvm/lib/IR/RuntimeLibcalls.cpp b/llvm/lib/IR/RuntimeLibcalls.cpp
index ac845c4998783..c63c77f3d9d61 100644
--- a/llvm/lib/IR/RuntimeLibcalls.cpp
+++ b/llvm/lib/IR/RuntimeLibcalls.cpp
@@ -10,6 +10,7 @@
#include "llvm/ADT/StringTable.h"
#include "llvm/Support/Debug.h"
#include "llvm/TargetParser/ARMTargetParser.h"
+#include "llvm/Support/xxhash.h"
#define DEBUG_TYPE "runtime-libcalls-info"
@@ -18,9 +19,11 @@ using namespace RTLIB;
#define GET_INIT_RUNTIME_LIBCALL_NAMES
#define GET_SET_TARGET_RUNTIME_LIBCALL_SETS
+#define DEFINE_GET_LOOKUP_LIBCALL_IMPL_NAME
#include "llvm/IR/RuntimeLibcalls.inc"
#undef GET_INIT_RUNTIME_LIBCALL_NAMES
#undef GET_SET_TARGET_RUNTIME_LIBCALL_SETS
+#undef DEFINE_GET_LOOKUP_LIBCALL_IMPL_NAME
/// Set default libcall names. If a target wants to opt-out of a libcall it
/// should be placed here.
@@ -58,49 +61,22 @@ void RuntimeLibcallsInfo::initLibcalls(const Triple &TT,
}
}
-RTLIB::LibcallImpl
-RuntimeLibcallsInfo::getSupportedLibcallImpl(StringRef FuncName) const {
- const ArrayRef<uint16_t> RuntimeLibcallNameOffsets(
- RuntimeLibcallNameOffsetTable);
-
- iterator_range<ArrayRef<uint16_t>::const_iterator> Range =
- getRecognizedLibcallImpls(FuncName);
-
- for (auto I = Range.begin(); I != Range.end(); ++I) {
- RTLIB::LibcallImpl Impl =
- static_cast<RTLIB::LibcallImpl>(I - RuntimeLibcallNameOffsets.begin());
-
- // FIXME: This should not depend on looking up ImplToLibcall, only the list
- // of libcalls for the module.
- RTLIB::LibcallImpl Recognized = LibcallImpls[ImplToLibcall[Impl]];
- if (Recognized != RTLIB::Unsupported)
- return Recognized;
+LLVM_ATTRIBUTE_ALWAYS_INLINE
+iota_range<RTLIB::LibcallImpl>
+RuntimeLibcallsInfo::libcallImplNameHit(uint16_t NameOffsetEntry,
+ uint16_t StrOffset) {
+ int NumAliases = 1;
+ for (int E = std::size(RuntimeLibcallNameOffsetTable);
+ NameOffsetEntry + NumAliases != E &&
+ RuntimeLibcallNameOffsetTable[NameOffsetEntry + NumAliases] == StrOffset;
+ ++NumAliases) {
}
- return RTLIB::Unsupported;
-}
-
-iterator_range<ArrayRef<uint16_t>::const_iterator>
-RuntimeLibcallsInfo::getRecognizedLibcallImpls(StringRef FuncName) {
- StringTable::Iterator It = lower_bound(RuntimeLibcallImplNameTable, FuncName);
- if (It == RuntimeLibcallImplNameTable.end() || *It != FuncName)
- return iterator_range(ArrayRef<uint16_t>());
-
- uint16_t IndexVal = It.offset().value();
- const ArrayRef<uint16_t> TableRef(RuntimeLibcallNameOffsetTable);
-
- ArrayRef<uint16_t>::const_iterator E = TableRef.end();
- ArrayRef<uint16_t>::const_iterator EntriesBegin =
- std::lower_bound(TableRef.begin(), E, IndexVal);
- ArrayRef<uint16_t>::const_iterator EntriesEnd = EntriesBegin;
-
- while (EntriesEnd != E && *EntriesEnd == IndexVal)
- ++EntriesEnd;
-
- assert(EntriesBegin != E &&
- "libcall found in name table but not offset table");
-
- return make_range(EntriesBegin, EntriesEnd);
+ RTLIB::LibcallImpl ImplStart = static_cast<RTLIB::LibcallImpl>(
+ &RuntimeLibcallNameOffsetTable[NameOffsetEntry] -
+ &RuntimeLibcallNameOffsetTable[0]);
+ return enum_seq(ImplStart,
+ static_cast<RTLIB::LibcallImpl>(ImplStart + NumAliases));
}
bool RuntimeLibcallsInfo::isAAPCS_ABI(const Triple &TT, StringRef ABIName) {
diff --git a/llvm/lib/Object/IRSymtab.cpp b/llvm/lib/Object/IRSymtab.cpp
index 0f194953787e6..7bba6f15dd1b5 100644
--- a/llvm/lib/Object/IRSymtab.cpp
+++ b/llvm/lib/Object/IRSymtab.cpp
@@ -54,6 +54,11 @@ static const char *PreservedSymbols[] = {
"__stack_chk_guard",
};
+static bool isPreservedGlobalVarName(StringRef Name) {
+ return StringRef(PreservedSymbols[0]) == Name ||
+ StringRef(PreservedSymbols[1]) == Name;
+}
+
namespace {
const char *getExpectedProducerName() {
@@ -81,12 +86,16 @@ struct Builder {
// The StringTableBuilder does not create a copy of any strings added to it,
// so this provides somewhere to store any strings that we create.
Builder(SmallVector<char, 0> &Symtab, StringTableBuilder &StrtabBuilder,
- BumpPtrAllocator &Alloc)
- : Symtab(Symtab), StrtabBuilder(StrtabBuilder), Saver(Alloc) {}
+ BumpPtrAllocator &Alloc, const Triple &TT)
+ : Symtab(Symtab), StrtabBuilder(StrtabBuilder), Saver(Alloc), TT(TT),
+ Libcalls(TT) {}
DenseMap<const Comdat *, int> ComdatMap;
Mangler Mang;
- Triple TT;
+ const Triple &TT;
+
+ // FIXME: This shouldn't be here.
+ RTLIB::RuntimeLibcallsInfo Libcalls;
std::vector<storage::Comdat> Comdats;
std::vector<storage::Module> Mods;
@@ -98,6 +107,10 @@ struct Builder {
std::vector<storage::Str> DependentLibraries;
+ bool isPreservedLibFuncName(StringRef Name) {
+ return Libcalls.getSupportedLibcallImpl(Name) != RTLIB::Unsupported;
+ }
+
void setStr(storage::Str &S, StringRef Value) {
S.Offset = StrtabBuilder.add(Value);
S.Size = Value.size();
@@ -213,19 +226,6 @@ Expected<int> Builder::getComdatIndex(const Comdat *C, const Module *M) {
return P.first->second;
}
-static StringSet<> buildPreservedSymbolsSet(const Triple &TT) {
- StringSet<> PreservedSymbolSet;
- PreservedSymbolSet.insert(std::begin(PreservedSymbols),
- std::end(PreservedSymbols));
- // FIXME: Do we need to pass in ABI fields from TargetOptions?
- RTLIB::RuntimeLibcallsInfo Libcalls(TT);
- for (RTLIB::LibcallImpl Impl : Libcalls.getLibcallImpls()) {
- if (Impl != RTLIB::Unsupported)
- PreservedSymbolSet.insert(Libcalls.getLibcallImplName(Impl));
- }
- return PreservedSymbolSet;
-}
-
Error Builder::addSymbol(const ModuleSymbolTable &Msymtab,
const SmallPtrSet<GlobalValue *, 4> &Used,
ModuleSymbolTable::Symbol Msym) {
@@ -279,13 +279,11 @@ Error Builder::addSymbol(const ModuleSymbolTable &Msymtab,
return Error::success();
}
- setStr(Sym.IRName, GV->getName());
-
- static const StringSet<> PreservedSymbolsSet =
- buildPreservedSymbolsSet(GV->getParent()->getTargetTriple());
- bool IsPreservedSymbol = PreservedSymbolsSet.contains(GV->getName());
+ StringRef GVName = GV->getName();
+ setStr(Sym.IRName, GVName);
- if (Used.count(GV) || IsPreservedSymbol)
+ if (Used.count(GV) || isPreservedLibFuncName(GVName) ||
+ isPreservedGlobalVarName(GVName))
Sym.Flags |= 1 << storage::Symbol::FB_used;
if (GV->isThreadLocal())
Sym.Flags |= 1 << storage::Symbol::FB_tls;
@@ -352,7 +350,6 @@ Error Builder::build(ArrayRef<Module *> IRMods) {
setStr(Hdr.Producer, kExpectedProducerName);
setStr(Hdr.TargetTriple, IRMods[0]->getTargetTriple().str());
setStr(Hdr.SourceFileName, IRMods[0]->getSourceFileName());
- TT = IRMods[0]->getTargetTriple();
for (auto *M : IRMods)
if (Error Err = addModule(M))
@@ -378,7 +375,8 @@ Error Builder::build(ArrayRef<Module *> IRMods) {
Error irsymtab::build(ArrayRef<Module *> Mods, SmallVector<char, 0> &Symtab,
StringTableBuilder &StrtabBuilder,
BumpPtrAllocator &Alloc) {
- return Builder(Symtab, StrtabBuilder, Alloc).build(Mods);
+ const Triple &TT = Mods[0]->getTargetTriple();
+ return Builder(Symtab, StrtabBuilder, Alloc, TT).build(Mods);
}
// Upgrade a vector of bitcode modules created by an old version of LLVM by
diff --git a/llvm/test/TableGen/RuntimeLibcallEmitter.td b/llvm/test/TableGen/RuntimeLibcallEmitter.td
index a2d946f3aa84f..54ca3f97e2d4b 100644
--- a/llvm/test/TableGen/RuntimeLibcallEmitter.td
+++ b/llvm/test/TableGen/RuntimeLibcallEmitter.td
@@ -149,6 +149,32 @@ def BlahLibrary : SystemRuntimeLibrary<isBlahArch, (add calloc, LibraryWithCondi
// CHECK-NEXT: RTLIB::SQRT_F80, // RTLIB::sqrtl_f80
// CHECK-NEXT: };
+// CHECK: #ifdef GET_LOOKUP_LIBCALL_IMPL_NAME_BODY
+// CHECK-NEXT: size_t Size = Name.size();
+// CHECK-NEXT: if (Size == 0 || Size > 9)
+// CHECK-NEXT: return enum_seq(RTLIB::Unsupported, RTLIB::Unsupported);
+// CHECK-NEXT: return lookupLibcallImplNameImpl(Name);
+// CHECK-NEXT: #endif
+
+// CHECK: #ifdef DEFINE_GET_LOOKUP_LIBCALL_IMPL_NAME
+// CHECK-NEXT: static inline uint64_t hash(StringRef Str) {
+// CHECK-NEXT: return static_cast<uint32_t>(xxh3_64bits(Str));
+// CHECK-NEXT: }
+
+// CHECK: iota_range<RTLIB::LibcallImpl> RTLIB::RuntimeLibcallsInfo::lookupLibcallImplNameImpl(StringRef Name) {
+// CHECK: static constexpr std::pair<uint16_t, uint16_t> HashTableNameToEnum[16] = {
+// CHECK: {2, 9}, // 0x000000705301b8, ___memset
+// CHECK: {0, 0},
+// CHECK: {6, 6}, // 0x0000001417a2af, calloc
+// CHECK: {0, 0},
+// CHECK: };
+
+// CHECK: unsigned Idx = (hash(Name) % 8) * 2;
+// CHECK: for (int I = 0; I != 2; ++I) {
+// CHECK: return libcallImplNameHit(Entry, StrOffset);
+
+// CHECK: return enum_seq(RTLIB::Unsupported, RTLIB::Unsupported);
+// CHECK-NEXT: }
// CHECK: void llvm::RTLIB::RuntimeLibcallsInfo::setTargetRuntimeLibcallSets(const llvm::Triple &TT, FloatABI::ABIType FloatABI, EABI EABIVersion, StringRef ABIName) {
// CHECK-NEXT: struct LibcallImplPair {
diff --git a/llvm/unittests/IR/CMakeLists.txt b/llvm/unittests/IR/CMakeLists.txt
index b66eae93f9339..8b7bd3997ea27 100644
--- a/llvm/unittests/IR/CMakeLists.txt
+++ b/llvm/unittests/IR/CMakeLists.txt
@@ -43,6 +43,7 @@ add_llvm_unittest(IRTests
PatternMatch.cpp
ShuffleVectorInstTest.cpp
StructuralHashTest.cpp
+ RuntimeLibcallsTest.cpp
TimePassesTest.cpp
TypesTest.cpp
UseTest.cpp
diff --git a/llvm/unittests/IR/RuntimeLibcallsTest.cpp b/llvm/unittests/IR/RuntimeLibcallsTest.cpp
new file mode 100644
index 0000000000000..1ef79e74f9a4b
--- /dev/null
+++ b/llvm/unittests/IR/RuntimeLibcallsTest.cpp
@@ -0,0 +1,63 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/IR/RuntimeLibcalls.h"
+#include "llvm/ADT/STLExtras.h"
+#include "gtest/gtest.h"
+using namespace llvm;
+
+namespace {
+
+TEST(RuntimeLibcallsTest, LibcallImplByName) {
+ EXPECT_TRUE(RTLIB::RuntimeLibcallsInfo::lookupLibcallImplName("").empty());
+ EXPECT_TRUE(
+ RTLIB::RuntimeLibcallsInfo::lookupLibcallImplName("unknown").empty());
+ EXPECT_TRUE(
+ RTLIB::RuntimeLibcallsInfo::lookupLibcallImplName("Unsupported").empty());
+ EXPECT_TRUE(
+ RTLIB::RuntimeLibcallsInfo::lookupLibcallImplName("unsupported").empty());
+
+ for (RTLIB::LibcallImpl LC : RTLIB::libcall_impls()) {
+ const char *Name = RTLIB::RuntimeLibcallsInfo::getLibcallImplName(LC);
+ EXPECT_FALSE(
+ RTLIB::RuntimeLibcallsInfo::lookupLibcallImplName(Name).empty());
+ }
+
+ // Test first libcall name
+ EXPECT_EQ(
+ RTLIB::arm64ec__Unwind_Resume,
+ *RTLIB::RuntimeLibcallsInfo::lookupLibcallImplName("#_Unwind_Resume")
+ .begin());
+ // Test longest libcall names
+ EXPECT_EQ(RTLIB::__hexagon_memcpy_likely_aligned_min32bytes_mult8bytes,
+ *RTLIB::RuntimeLibcallsInfo::lookupLibcallImplName(
+ "__hexagon_memcpy_likely_aligned_min32bytes_mult8bytes")
+ .begin());
+
+ {
+ auto SquirtleSquad =
+ RTLIB::RuntimeLibcallsInfo::lookupLibcallImplName("sqrtl");
+ ASSERT_EQ(size(SquirtleSquad), 3);
+ auto I = SquirtleSquad.begin();
+ EXPECT_EQ(*I++, RTLIB::sqrt_f128);
+ EXPECT_EQ(*I++, RTLIB::sqrt_f80);
+ EXPECT_EQ(*I++, RTLIB::sqrt_ppcf128);
+ }
+
+ // Last libcall
+ {
+ auto Truncs = RTLIB::RuntimeLibcallsInfo::lookupLibcallImplName("truncl");
+ ASSERT_EQ(size(Truncs), 3);
+ auto I = Truncs.begin();
+ EXPECT_EQ(*I++, RTLIB::trunc_f128);
+ EXPECT_EQ(*I++, RTLIB::trunc_f80);
+ EXPECT_EQ(*I++, RTLIB::trunc_ppcf128);
+ }
+}
+
+} // namespace
diff --git a/llvm/utils/TableGen/Basic/RuntimeLibcallsEmitter.cpp b/llvm/utils/TableGen/Basic/RuntimeLibcallsEmitter.cpp
index 0fc230c4714f0..92e37545c9360 100644
--- a/llvm/utils/TableGen/Basic/RuntimeLibcallsEmitter.cpp
+++ b/llvm/utils/TableGen/Basic/RuntimeLibcallsEmitter.cpp
@@ -6,10 +6,15 @@
//
//===----------------------------------------------------------------------===//
+#define DEBUG_TYPE "runtime-libcall-emitter"
+
+#include "llvm/ADT/DenseSet.h"
#include "llvm/ADT/StringRef.h"
#include "llvm/Support/Debug.h"
+#include "llvm/Support/Format.h"
#include "llvm/Support/FormatVariadic.h"
#include "llvm/Support/raw_ostream.h"
+#include "llvm/Support/xxhash.h"
#include "llvm/TableGen/Error.h"
#include "llvm/TableGen/Record.h"
#include "llvm/TableGen/SetTheory.h"
@@ -215,6 +220,9 @@ class RuntimeLibcallEmitter {
private:
void emitGetRuntimeLibcallEnum(raw_ostream &OS) const;
+ void emitNameMatchHashTable(raw_ostream &OS,
+ StringToOffsetTable &OffsetTable) const;
+
void emitGetInitRuntimeLibcallNames(raw_ostream &OS) const;
void emitSystemRuntimeLibrarySetCalls(raw_ostream &OS) const;
@@ -255,12 +263,9 @@ class RuntimeLibcallEmitter {
RuntimeLibcallImplDefList.emplace_back(LibCallImplDef, Def2RuntimeLibcall,
LibCallImplEnumVal++);
- RuntimeLibcallImpl &LibCallImpl = RuntimeLibcallImplDefList.back();
-
+ const RuntimeLibcallImpl &LibCallImpl = RuntimeLibcallImplDefList.back();
Def2RuntimeLibcallImpl[LibCallImplDef] = &LibCallImpl;
- // const RuntimeLibcallImpl &LibCallImpl =
- // RuntimeLibcallImplDefList.back();
if (LibCallImpl.isDefault()) {
const RuntimeLibcall *Provides = LibCallImpl.getProvides();
if (!Provides)
@@ -282,6 +287,13 @@ class RuntimeLibcallEmitter {
void run(raw_ostream &OS);
};
+/// Helper struct for the name hash table.
+struct LookupEntry {
+ StringRef FuncName;
+ uint64_t Hash = 0;
+ unsigned TableValue = 0;
+};
+
} // End anonymous namespace.
void RuntimeLibcallEmitter::emitGetRuntimeLibcallEnum(raw_ostream &OS) const {
@@ -295,8 +307,6 @@ void RuntimeLibcallEmitter::emitGetRuntimeLibcallEnum(raw_ostream &OS) const {
OS << " " << Name << " = " << LibCall.getEnumVal() << ",\n";
}
- // TODO: Emit libcall names as string offset table.
-
OS << " UNKNOWN_LIBCALL = " << RuntimeLibcallDefList.size()
<< "\n};\n\n"
"enum LibcallImpl : unsigned short {\n"
@@ -315,8 +325,183 @@ void RuntimeLibcallEmitter::emitGetRuntimeLibcallEnum(raw_ostream &OS) const {
"#endif\n\n";
}
+// StringMap uses xxh3_64bits, truncated to uint32_t.
+static uint64_t hash(StringRef Str) {
+ return static_cast<uint32_t>(xxh3_64bits(Str));
+}
+
+static void emitHashFunction(raw_ostream &OS) {
+ OS << "static inline uint64_t hash(StringRef Str) {\n"
+ " return static_cast<uint32_t>(xxh3_64bits(Str));\n"
+ "}\n\n";
+}
+
+/// Return the table size, maximum number of collisions for the set of hashes
+static std::pair<int, int>
+computePerfectHashParameters(ArrayRef<uint64_t> Hashes) {
+ const int SizeOverhead = 10;
+ const int NumHashes = Hashes.size();
+
+ // Index derived from hash -> number of collisions.
+ DenseMap<uint64_t, int> Table;
+
+ for (int MaxCollisions = 1;; ++MaxCollisions) {
+ for (int N = NumHashes; N < SizeOverhead * NumHashes; ++N) {
+ Table.clear();
+
+ bool NeedResize = false;
+ for (uint64_t H : Hashes) {
+ uint64_t Idx = H % static_cast<uint64_t>(N);
+ if (++Table[Idx] > MaxCollisions) {
+ // Need to resize the final table if we increased the collision count.
+ NeedResize = true;
+ break;
+ }
+ }
+
+ if (!NeedResize)
+ return {N, MaxCollisions};
+ }
+ }
+
+ llvm_unreachable("loop should terminate");
+}
+
+static std::vector<LookupEntry>
+constructPerfectHashTable(ArrayRef<RuntimeLibcallImpl> Keywords,
+ ArrayRef<uint64_t> Hashes, int Size, int Collisions,
+ StringToOffsetTable &OffsetTable) {
+ DenseSet<StringRef> Seen;
+ std::vector<LookupEntry> Lookup(Size * Collisions);
+
+ for (const RuntimeLibcallImpl &LibCallImpl : Keywords) {
+ StringRef ImplName = LibCallImpl.getLibcallFuncName();
+
+ // We do not want to add repeated entries for cases with the same name, only
+ // an entry for the first, with the name collision enum values immediately
+ // following.
+ if (!Seen.insert(ImplName).second)
+ continue;
+
+ uint64_t HashValue = Hashes[LibCallImpl.getEnumVal() - 1];
+
+ uint64_t Idx = (HashValue % static_cast<uint64_t>(Size)) *
+ static_cast<uint64_t>(Collisions);
+
+ bool Found = false;
+ for (int J = 0; J < Collisions; ++J) {
+ LookupEntry &Entry = Lookup[Idx + J];
+ if (Entry.TableValue == 0) {
+ Entry.FuncName = ImplName;
+ Entry.TableValue = LibCallImpl.getEnumVal();
+ Entry.Hash = HashValue;
+ Found = true;
+ break;
+ }
+ }
+
+ if (!Found)
+ reportFatalInternalError("failure to hash " + ImplName);
+ }
+
+ return Lookup;
+}
+
+/// Generate hash table based lookup by name.
+void RuntimeLibcallEmitter::emitNameMatchHashTable(
+ raw_ostream &OS, StringToOffsetTable &OffsetTable) const {
+ std::vector<uint64_t> Hashes(RuntimeLibcallImplDefList.size());
+
+ size_t MaxFuncNameSize = 0;
+ size_t Index = 0;
+ for (const RuntimeLibcallImpl &LibCallImpl : RuntimeLibcallImplDefList) {
+ StringRef ImplName = LibCallImpl.getLibcallFuncName();
+ MaxFuncNameSize = std::max(MaxFuncNameSize, ImplName.size());
+ Hashes[Index++] = hash(ImplName);
+ }
+
+ LLVM_DEBUG({
+ for (const RuntimeLibcallImpl &LibCallImpl : RuntimeLibcallImplDefList) {
+ StringRef ImplName = LibCallImpl.getLibcallFuncName();
+ if (ImplName.size() == MaxFuncNameSize) {
+ dbgs() << "Maximum runtime libcall name size: " << ImplName << '('
+ << MaxFuncNameSize << ")\n";
+ }
+ }
+ });
+
+ // Early exiting on the symbol name provides a significant speedup in the miss
+ // case on the set of symbols in a clang binary. Emit this as an inlinable
+ // precondition in the header.
+ //
+ // The empty check is also used to get sensible behavior on anonymous
+ // functions.
+ //
+ // TODO: It may make more sense to split the search by string size more. There
+ // are a few outliers, most call names are small.
+ OS << "#ifdef GET_LOOKUP_LIBCALL_IMPL_NAME_BODY\n"
+ " size_t Size = Name.size();\n"
+ " if (Size == 0 || Size > "
+ << MaxFuncNameSize
+ << ")\n"
+ " return enum_seq(RTLIB::Unsupported, RTLIB::Unsupported);\n"
+ " return lookupLibcallImplNameImpl(Name);\n"
+ "#endif\n";
+
+ auto [Size, Collisions] = computePerfectHashParameters(Hashes);
+ std::vector<LookupEntry> Lookup = constructPerfectHashTable(
+ RuntimeLibcallImplDefList, Hashes, Size, Collisions, OffsetTable);
+
+ LLVM_DEBUG(dbgs() << "Runtime libcall perfect hashing parameters: Size = "
+ << Size << ", maximum collisions = " << Collisions << '\n');
+
+ OS << "#ifdef DEFINE_GET_LOOKUP_LIBCALL_IMPL_NAME\n";
+ emitHashFunction(OS);
+
+ OS << "iota_range<RTLIB::LibcallImpl> RTLIB::RuntimeLibcallsInfo::"
+ "lookupLibcallImplNameImpl(StringRef Name) {\n";
+
+ // Emit pair of RTLIB::LibcallImpl, size of the string name. It's important to
+ // avoid strlen on the string table entries.
+ OS << " static constexpr std::pair<uint16_t, uint16_t> HashTableNameToEnum["
+ << Lookup.size() << "] = {\n";
+
+ for (auto [FuncName, Hash, TableVal] : Lookup) {
+ OS << " {" << TableVal << ", " << FuncName.size() << "},";
+
+ if (TableVal != 0) {
+ OS << " // " << format_hex(Hash, 16) << ", " << FuncName;
+ }
+
+ OS << '\n';
+ }
+
+ OS << " };\n\n";
+
+ OS << " unsigned Idx = (hash(Name) % " << Size << ") * " << Collisions
+ << ";\n\n"
+ " for (int I = 0; I != "
+ << Collisions << R"(; ++I) {
+ auto [Entry, StringSize] = HashTableNameToEnum[Idx + I];
+ const uint16_t StrOffset = RuntimeLibcallNameOffsetTable[Entry];
+ StringRef Str(
+ &RTLIB::RuntimeLibcallsInfo::RuntimeLibcallImplNameTableStorage[StrOffset],
+ StringSize);
+ if (Str == Name)
+ return libcallImplNameHit(Entry, StrOffset);
+ }
+
+ return enum_seq(RTLIB::Unsupported, RTLIB::Unsupported);
+}
+)";
+
+ OS << "#endif\n\n";
+}
+
void RuntimeLibcallEmitter::emitGetInitRuntimeLibcallNames(
raw_ostream &OS) const {
+ OS << "#ifdef GET_INIT_RUNTIME_LIBCALL_NAMES\n";
+
// Emit the implementation names
StringToOffsetTable Table(/*AppendZero=*/true,
"RTLIB::RuntimeLibcallsInfo::");
@@ -351,6 +536,10 @@ const uint16_t RTLIB::RuntimeLibcallsInfo::RuntimeLibcallNameOffsetTable[] = {
OS << '\n';
}
OS << "};\n\n";
+
+ OS << "#endif\n\n";
+
+ emitNameMatchHashTable(OS, Table);
}
void RuntimeLibcallEmitter::emitSystemRuntimeLibrarySetCalls(
@@ -531,9 +720,7 @@ void RuntimeLibcallEmitter::run(raw_ostream &OS) {
emitSourceFileHeader("Runtime LibCalls Source Fragment", OS, Records);
emitGetRuntimeLibcallEnum(OS);
- OS << "#ifdef GET_INIT_RUNTIME_LIBCALL_NAMES\n";
emitGetInitRuntimeLibcallNames(OS);
- OS << "#endif\n\n";
OS << "#ifdef GET_SET_TARGET_RUNTIME_LIBCALL_SETS\n";
emitSystemRuntimeLibrarySetCalls(OS);
>From bb169581d2c01793d3b7e5b94889211e072d88cc Mon Sep 17 00:00:00 2001
From: Matt Arsenault <Matthew.Arsenault at amd.com>
Date: Wed, 13 Aug 2025 10:55:05 +0900
Subject: [PATCH 2/6] Use StringLiteral and constexpr
---
llvm/lib/Object/IRSymtab.cpp | 7 +++----
1 file changed, 3 insertions(+), 4 deletions(-)
diff --git a/llvm/lib/Object/IRSymtab.cpp b/llvm/lib/Object/IRSymtab.cpp
index 7bba6f15dd1b5..52fcd0ec36402 100644
--- a/llvm/lib/Object/IRSymtab.cpp
+++ b/llvm/lib/Object/IRSymtab.cpp
@@ -46,7 +46,7 @@ static cl::opt<bool> DisableBitcodeVersionUpgrade(
"disable-bitcode-version-upgrade", cl::Hidden,
cl::desc("Disable automatic bitcode upgrade for version mismatch"));
-static const char *PreservedSymbols[] = {
+static constexpr StringLiteral PreservedSymbols[] = {
// There are global variables, so put it here instead of in
// RuntimeLibcalls.td.
// TODO: Are there similar such variables?
@@ -54,9 +54,8 @@ static const char *PreservedSymbols[] = {
"__stack_chk_guard",
};
-static bool isPreservedGlobalVarName(StringRef Name) {
- return StringRef(PreservedSymbols[0]) == Name ||
- StringRef(PreservedSymbols[1]) == Name;
+static constexpr bool isPreservedGlobalVarName(StringRef Name) {
+ return PreservedSymbols[0] == Name || PreservedSymbols[1] == Name;
}
namespace {
>From 96c279f3b724f10189512cc0defea5c5253d216a Mon Sep 17 00:00:00 2001
From: Matt Arsenault <Matthew.Arsenault at amd.com>
Date: Wed, 13 Aug 2025 10:56:21 +0900
Subject: [PATCH 3/6] loop suggestion
---
llvm/lib/IR/RuntimeLibcalls.cpp | 9 +++++----
1 file changed, 5 insertions(+), 4 deletions(-)
diff --git a/llvm/lib/IR/RuntimeLibcalls.cpp b/llvm/lib/IR/RuntimeLibcalls.cpp
index c63c77f3d9d61..128ce465f3b8c 100644
--- a/llvm/lib/IR/RuntimeLibcalls.cpp
+++ b/llvm/lib/IR/RuntimeLibcalls.cpp
@@ -66,10 +66,11 @@ iota_range<RTLIB::LibcallImpl>
RuntimeLibcallsInfo::libcallImplNameHit(uint16_t NameOffsetEntry,
uint16_t StrOffset) {
int NumAliases = 1;
- for (int E = std::size(RuntimeLibcallNameOffsetTable);
- NameOffsetEntry + NumAliases != E &&
- RuntimeLibcallNameOffsetTable[NameOffsetEntry + NumAliases] == StrOffset;
- ++NumAliases) {
+ for (uint16_t Entry : ArrayRef(RuntimeLibcallNameOffsetTable)
+ .drop_front(NameOffsetEntry + 1)) {
+ if (Entry != StrOffset)
+ break;
+ ++NumAliases;
}
RTLIB::LibcallImpl ImplStart = static_cast<RTLIB::LibcallImpl>(
>From 67e1dbd2dfab3ac9c37d4a31b52d481126b0efe3 Mon Sep 17 00:00:00 2001
From: Matt Arsenault <Matthew.Arsenault at amd.com>
Date: Wed, 13 Aug 2025 16:49:52 +0900
Subject: [PATCH 4/6] Fix bad constexpr
---
llvm/lib/Object/IRSymtab.cpp | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/llvm/lib/Object/IRSymtab.cpp b/llvm/lib/Object/IRSymtab.cpp
index 52fcd0ec36402..0043f02107fb8 100644
--- a/llvm/lib/Object/IRSymtab.cpp
+++ b/llvm/lib/Object/IRSymtab.cpp
@@ -54,7 +54,7 @@ static constexpr StringLiteral PreservedSymbols[] = {
"__stack_chk_guard",
};
-static constexpr bool isPreservedGlobalVarName(StringRef Name) {
+static bool isPreservedGlobalVarName(StringRef Name) {
return PreservedSymbols[0] == Name || PreservedSymbols[1] == Name;
}
>From 51e3a1e5ad9442177d2d9132da744769f2e4b6ed Mon Sep 17 00:00:00 2001
From: Matt Arsenault <Matthew.Arsenault at amd.com>
Date: Thu, 14 Aug 2025 08:39:04 +0900
Subject: [PATCH 5/6] Remove llvm_unreachable
---
llvm/utils/TableGen/Basic/RuntimeLibcallsEmitter.cpp | 2 --
1 file changed, 2 deletions(-)
diff --git a/llvm/utils/TableGen/Basic/RuntimeLibcallsEmitter.cpp b/llvm/utils/TableGen/Basic/RuntimeLibcallsEmitter.cpp
index 92e37545c9360..775cef22db0b6 100644
--- a/llvm/utils/TableGen/Basic/RuntimeLibcallsEmitter.cpp
+++ b/llvm/utils/TableGen/Basic/RuntimeLibcallsEmitter.cpp
@@ -363,8 +363,6 @@ computePerfectHashParameters(ArrayRef<uint64_t> Hashes) {
return {N, MaxCollisions};
}
}
-
- llvm_unreachable("loop should terminate");
}
static std::vector<LookupEntry>
>From 889671328ad3ff77e932362107d7b4bffcb408da Mon Sep 17 00:00:00 2001
From: Matt Arsenault <Matthew.Arsenault at amd.com>
Date: Thu, 14 Aug 2025 11:31:22 +0900
Subject: [PATCH 6/6] RuntimeLibcalls: Improve unit test
---
llvm/unittests/IR/RuntimeLibcallsTest.cpp | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/llvm/unittests/IR/RuntimeLibcallsTest.cpp b/llvm/unittests/IR/RuntimeLibcallsTest.cpp
index 1ef79e74f9a4b..94ed56e92bd55 100644
--- a/llvm/unittests/IR/RuntimeLibcallsTest.cpp
+++ b/llvm/unittests/IR/RuntimeLibcallsTest.cpp
@@ -24,8 +24,8 @@ TEST(RuntimeLibcallsTest, LibcallImplByName) {
for (RTLIB::LibcallImpl LC : RTLIB::libcall_impls()) {
const char *Name = RTLIB::RuntimeLibcallsInfo::getLibcallImplName(LC);
- EXPECT_FALSE(
- RTLIB::RuntimeLibcallsInfo::lookupLibcallImplName(Name).empty());
+ EXPECT_TRUE(is_contained(
+ RTLIB::RuntimeLibcallsInfo::lookupLibcallImplName(Name), LC));
}
// Test first libcall name
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