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[IR] Adds Function::splice() member functions
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This is part of a series of patches that aim at making Function::getBasicBlockList() private.

Differential Revision: https://reviews.llvm.org/D139982
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@vporpo
vporpo committed Dec 14, 2022
1 parent 9408164 commit 7b68411
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22 changes: 22 additions & 0 deletions llvm/include/llvm/IR/Function.h
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Expand Up @@ -693,6 +693,28 @@ class LLVM_EXTERNAL_VISIBILITY Function : public GlobalObject,
return BasicBlocks.insert(Position, BB);
}

/// Transfer all blocks from \p FromF to this function at \p ToIt.
void splice(Function::iterator ToIt, Function *FromF) {
splice(ToIt, FromF, FromF->begin(), FromF->end());
}

/// Transfer one BasicBlock from \p FromF at \p FromIt to this function
/// at \p ToIt.
void splice(Function::iterator ToIt, Function *FromF,
Function::iterator FromIt) {
auto FromItNext = std::next(FromIt);
// Single-element splice is a noop if destination == source.
if (ToIt == FromIt || ToIt == FromItNext)
return;
splice(ToIt, FromF, FromIt, FromItNext);
}

/// Transfer a range of basic blocks that belong to \p FromF from \p
/// FromBeginIt to \p FromEndIt, to this function at \p ToIt.
void splice(Function::iterator ToIt, Function *FromF,
Function::iterator FromBeginIt,
Function::iterator FromEndIt);

/// Get the underlying elements of the Function... the basic block list is
/// empty for external functions.
///
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12 changes: 12 additions & 0 deletions llvm/lib/IR/Function.cpp
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Expand Up @@ -368,6 +368,18 @@ void Function::eraseFromParent() {
getParent()->getFunctionList().erase(getIterator());
}

void Function::splice(Function::iterator ToIt, Function *FromF,
Function::iterator FromBeginIt,
Function::iterator FromEndIt) {
#ifdef EXPENSIVE_CHECKS
// Check that FromBeginIt is before FromEndIt.
auto FromFEnd = FromF->end();
for (auto It = FromBeginIt; It != FromEndIt; ++It)
assert(It != FromBBEnd && "FromBeginIt not before FromEndIt!");
#endif // EXPENSIVE_CHECKS
BasicBlocks.splice(ToIt, FromF->BasicBlocks, FromBeginIt, FromEndIt);
}

//===----------------------------------------------------------------------===//
// Function Implementation
//===----------------------------------------------------------------------===//
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207 changes: 207 additions & 0 deletions llvm/unittests/IR/FunctionTest.cpp
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Expand Up @@ -239,4 +239,211 @@ define void @bar() {
EXPECT_EQ(It, FooBB0->getIterator());
}

TEST(FunctionTest, SpliceOneBB) {
LLVMContext Ctx;
std::unique_ptr<Module> M = parseIR(Ctx, R"(
define void @from() {
from_bb1:
br label %from_bb2
from_bb2:
br label %from_bb3
from_bb3:
ret void
}
define void @to() {
to_bb1:
br label %to_bb2
to_bb2:
br label %to_bb3
to_bb3:
ret void
}
)");
Function *FromF = M->getFunction("from");
BasicBlock *FromBB1 = getBBWithName(FromF, "from_bb1");
BasicBlock *FromBB2 = getBBWithName(FromF, "from_bb2");
BasicBlock *FromBB3 = getBBWithName(FromF, "from_bb3");

Function *ToF = M->getFunction("to");
BasicBlock *ToBB1 = getBBWithName(ToF, "to_bb1");
BasicBlock *ToBB2 = getBBWithName(ToF, "to_bb2");
BasicBlock *ToBB3 = getBBWithName(ToF, "to_bb3");

// Move from_bb2 before to_bb1.
ToF->splice(ToBB1->getIterator(), FromF, FromBB2->getIterator());
EXPECT_EQ(FromF->size(), 2u);
EXPECT_EQ(ToF->size(), 4u);

auto It = FromF->begin();
EXPECT_EQ(&*It++, FromBB1);
EXPECT_EQ(&*It++, FromBB3);

It = ToF->begin();
EXPECT_EQ(&*It++, FromBB2);
EXPECT_EQ(&*It++, ToBB1);
EXPECT_EQ(&*It++, ToBB2);
EXPECT_EQ(&*It++, ToBB3);

// Cleanup to avoid "Uses remain when a value is destroyed!".
FromF->splice(FromBB3->getIterator(), ToF, FromBB2->getIterator());
}

TEST(FunctionTest, SpliceOneBBWhenFromIsSameAsTo) {
LLVMContext Ctx;
std::unique_ptr<Module> M = parseIR(Ctx, R"(
define void @fromto() {
bb1:
br label %bb2
bb2:
ret void
}
)");
Function *F = M->getFunction("fromto");
BasicBlock *BB1 = getBBWithName(F, "bb1");
BasicBlock *BB2 = getBBWithName(F, "bb2");

// According to ilist's splice() a single-element splice where dst == src
// should be a noop.
F->splice(BB1->getIterator(), F, BB1->getIterator());

auto It = F->begin();
EXPECT_EQ(&*It++, BB1);
EXPECT_EQ(&*It++, BB2);
EXPECT_EQ(F->size(), 2u);
}

TEST(FunctionTest, SpliceLastBB) {
LLVMContext Ctx;
std::unique_ptr<Module> M = parseIR(Ctx, R"(
define void @from() {
from_bb1:
br label %from_bb2
from_bb2:
br label %from_bb3
from_bb3:
ret void
}
define void @to() {
to_bb1:
br label %to_bb2
to_bb2:
br label %to_bb3
to_bb3:
ret void
}
)");

Function *FromF = M->getFunction("from");
BasicBlock *FromBB1 = getBBWithName(FromF, "from_bb1");
BasicBlock *FromBB2 = getBBWithName(FromF, "from_bb2");
BasicBlock *FromBB3 = getBBWithName(FromF, "from_bb3");

Function *ToF = M->getFunction("to");
BasicBlock *ToBB1 = getBBWithName(ToF, "to_bb1");
BasicBlock *ToBB2 = getBBWithName(ToF, "to_bb2");
BasicBlock *ToBB3 = getBBWithName(ToF, "to_bb3");

// Move from_bb2 before to_bb1.
auto ToMove = FromBB2->getIterator();
ToF->splice(ToBB1->getIterator(), FromF, ToMove, std::next(ToMove));

EXPECT_EQ(FromF->size(), 2u);
auto It = FromF->begin();
EXPECT_EQ(&*It++, FromBB1);
EXPECT_EQ(&*It++, FromBB3);

EXPECT_EQ(ToF->size(), 4u);
It = ToF->begin();
EXPECT_EQ(&*It++, FromBB2);
EXPECT_EQ(&*It++, ToBB1);
EXPECT_EQ(&*It++, ToBB2);
EXPECT_EQ(&*It++, ToBB3);

// Cleanup to avoid "Uses remain when a value is destroyed!".
FromF->splice(FromBB3->getIterator(), ToF, ToMove);
}

TEST(FunctionTest, SpliceBBRange) {
LLVMContext Ctx;
std::unique_ptr<Module> M = parseIR(Ctx, R"(
define void @from() {
from_bb1:
br label %from_bb2
from_bb2:
br label %from_bb3
from_bb3:
ret void
}
define void @to() {
to_bb1:
br label %to_bb2
to_bb2:
br label %to_bb3
to_bb3:
ret void
}
)");

Function *FromF = M->getFunction("from");
BasicBlock *FromBB1 = getBBWithName(FromF, "from_bb1");
BasicBlock *FromBB2 = getBBWithName(FromF, "from_bb2");
BasicBlock *FromBB3 = getBBWithName(FromF, "from_bb3");

Function *ToF = M->getFunction("to");
BasicBlock *ToBB1 = getBBWithName(ToF, "to_bb1");
BasicBlock *ToBB2 = getBBWithName(ToF, "to_bb2");
BasicBlock *ToBB3 = getBBWithName(ToF, "to_bb3");

// Move all BBs from @from to @to.
ToF->splice(ToBB2->getIterator(), FromF, FromF->begin(), FromF->end());

EXPECT_EQ(FromF->size(), 0u);

EXPECT_EQ(ToF->size(), 6u);
auto It = ToF->begin();
EXPECT_EQ(&*It++, ToBB1);
EXPECT_EQ(&*It++, FromBB1);
EXPECT_EQ(&*It++, FromBB2);
EXPECT_EQ(&*It++, FromBB3);
EXPECT_EQ(&*It++, ToBB2);
EXPECT_EQ(&*It++, ToBB3);
}

#ifdef EXPENSIVE_CHECKS
TEST(FunctionTest, SpliceEndBeforeBegin) {
LLVMContext Ctx;
std::unique_ptr<Module> M = parseIR(Ctx, R"(
define void @from() {
from_bb1:
br label %from_bb2
from_bb2:
br label %from_bb3
from_bb3:
ret void
}
define void @to() {
to_bb1:
br label %to_bb2
to_bb2:
br label %to_bb3
to_bb3:
ret void
}
)");

Function *FromF = M->getFunction("from");
BasicBlock *FromBB1 = getBBWithName(FromF, "from_bb1");
BasicBlock *FromBB2 = getBBWithName(FromF, "from_bb2");
BasicBlock *FromBB3 = getBBWithName(FromF, "from_bb3");

Function *ToF = M->getFunction("to");
BasicBlock *ToBB1 = getBBWithName(ToF, "to_bb1");
BasicBlock *ToBB2 = getBBWithName(ToF, "to_bb2");
BasicBlock *ToBB3 = getBBWithName(ToF, "to_bb3");

EXPECT_DEATH(ToF->splice(ToBB2->getIterator(), FromF, FromBB2->getIterator(),
FromBB1->getIterator()),
"FromBeginIt not before FromEndIt!");
}
#endif //EXPENSIVE_CHECKS
} // end namespace

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