llvm-project/llvm/unittests/CGData/StableFunctionMapTest.cpp
Kyungwoo Lee d23c5c2d65
[CGData] Global Merge Functions (#112671)
This implements a global function merging pass. Unlike traditional
function merging passes that use IR comparators, this pass employs a
structurally stable hash to identify similar functions while ignoring
certain constant operands. These ignored constants are tracked and
encoded into a stable function summary. When merging, instead of
explicitly folding similar functions and their call sites, we form a
merging instance by supplying different parameters via thunks. The
actual size reduction occurs when identically created merging instances
are folded by the linker.

Currently, this pass is wired to a pre-codegen pass, enabled by the
`-enable-global-merge-func` flag.
In a local merging mode, the analysis and merging steps occur
sequentially within a module:
- `analyze`: Collects stable function hashes and tracks locations of
ignored constant operands.
- `finalize`: Identifies merge candidates with matching hashes and
computes the set of parameters that point to different constants.
- `merge`: Uses the stable function map to optimistically create a
merged function.

We can enable a global merging mode similar to the global function
outliner
(https://discourse.llvm.org/t/rfc-enhanced-machine-outliner-part-2-thinlto-nolto/78753/),
which will perform the above steps separately.
- `-codegen-data-generate`: During the first round of code generation,
we analyze local merging instances and publish their summaries.
- Offline using `llvm-cgdata` or at link-time, we can finalize all these
merging summaries that are combined to determine parameters.
- `-codegen-data-use`: During the second round of code generation, we
optimistically create merging instances within each module, and finally,
the linker folds identically created merging instances.

Depends on #112664
This is a patch for
https://discourse.llvm.org/t/rfc-global-function-merging/82608.
2024-11-13 17:34:07 -08:00

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//===- StableFunctionMapTest.cpp ------------------------------------------===//
//
// 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/CGData/StableFunctionMap.h"
#include "gmock/gmock-matchers.h"
#include "gmock/gmock.h"
#include "gtest/gtest.h"
using namespace llvm;
namespace {
using testing::Contains;
using testing::IsEmpty;
using testing::Key;
using testing::Not;
using testing::Pair;
using testing::SizeIs;
TEST(StableFunctionMap, Name) {
StableFunctionMap Map;
EXPECT_TRUE(Map.empty());
EXPECT_TRUE(Map.getNames().empty());
unsigned ID1 = Map.getIdOrCreateForName("Func1");
unsigned ID2 = Map.getIdOrCreateForName("Func2");
unsigned ID3 = Map.getIdOrCreateForName("Func1");
EXPECT_THAT(Map.getNames(), SizeIs(2));
// The different names should return different IDs.
EXPECT_NE(ID1, ID2);
// The same name should return the same ID.
EXPECT_EQ(ID1, ID3);
// The IDs should be valid.
EXPECT_EQ(*Map.getNameForId(ID1), "Func1");
EXPECT_EQ(*Map.getNameForId(ID2), "Func2");
}
TEST(StableFunctionMap, Insert) {
StableFunctionMap Map;
StableFunction Func1{1, "Func1", "Mod1", 2, {{{0, 1}, 3}}};
StableFunction Func2{1, "Func2", "Mod1", 2, {{{0, 1}, 2}}};
Map.insert(Func1);
Map.insert(Func2);
// We only have a unique hash, 1
EXPECT_THAT(Map, SizeIs(1));
// We have two functions with the same hash which are potentially mergeable.
EXPECT_EQ(Map.size(StableFunctionMap::SizeType::TotalFunctionCount), 2u);
EXPECT_EQ(Map.size(StableFunctionMap::SizeType::MergeableFunctionCount), 2u);
}
TEST(StableFunctionMap, Merge) {
StableFunctionMap Map1;
StableFunction Func1{1, "Func1", "Mod1", 2, {{{0, 1}, 3}}};
StableFunction Func2{1, "Func2", "Mod1", 2, {{{0, 1}, 2}}};
StableFunction Func3{2, "Func3", "Mod1", 2, {{{1, 1}, 2}}};
Map1.insert(Func1);
Map1.insert(Func2);
Map1.insert(Func3);
StableFunctionMap Map2;
StableFunction Func4{1, "Func4", "Mod2", 2, {{{0, 1}, 4}}};
StableFunction Func5{2, "Func5", "Mod2", 2, {{{1, 1}, 5}}};
StableFunction Func6{3, "Func6", "Mod2", 2, {{{1, 1}, 6}}};
Map2.insert(Func4);
Map2.insert(Func5);
Map2.insert(Func6);
// Merge two maps.
Map1.merge(Map2);
// We only have two unique hashes, 1, 2 and 3
EXPECT_THAT(Map1, SizeIs(3));
// We have total 6 functions.
EXPECT_EQ(Map1.size(StableFunctionMap::SizeType::TotalFunctionCount), 6u);
// We have 5 mergeable functions. Func6 only has a unique hash, 3.
EXPECT_EQ(Map1.size(StableFunctionMap::SizeType::MergeableFunctionCount), 5u);
}
TEST(StableFunctionMap, Finalize1) {
StableFunctionMap Map;
StableFunction Func1{1, "Func1", "Mod1", 2, {{{0, 1}, 3}}};
StableFunction Func2{1, "Func2", "Mod2", 3, {{{0, 1}, 2}}};
Map.insert(Func1);
Map.insert(Func2);
// Instruction count is mis-matched, so they're not mergeable.
Map.finalize();
EXPECT_THAT(Map, IsEmpty());
}
TEST(StableFunctionMap, Finalize2) {
StableFunctionMap Map;
StableFunction Func1{1, "Func1", "Mod1", 2, {{{0, 1}, 3}}};
StableFunction Func2{1, "Func2", "Mod2", 2, {{{0, 1}, 2}, {{1, 1}, 1}}};
Map.insert(Func1);
Map.insert(Func2);
// Operand map size is mis-matched, so they're not mergeable.
Map.finalize();
EXPECT_THAT(Map, IsEmpty());
}
TEST(StableFunctionMap, Finalize3) {
StableFunctionMap Map;
StableFunction Func1{1, "Func1", "Mod1", 12, {{{0, 1}, 3}, {{1, 1}, 1}}};
StableFunction Func2{1, "Func2", "Mod2", 12, {{{0, 1}, 2}, {{1, 1}, 1}}};
Map.insert(Func1);
Map.insert(Func2);
// The same operand entry is removed, which is redundant.
Map.finalize();
auto &M = Map.getFunctionMap();
EXPECT_THAT(M, SizeIs(1));
auto &FuncEntries = M.begin()->second;
for (auto &FuncEntry : FuncEntries) {
EXPECT_THAT(*FuncEntry->IndexOperandHashMap, SizeIs(1));
ASSERT_THAT(*FuncEntry->IndexOperandHashMap,
Not(Contains(Key(Pair(1, 1)))));
}
}
} // end namespace