forked from OSchip/llvm-project
[gcov] Don't split entry block; add a synthetic entry block instead
The entry block is split at the first instruction where `shouldKeepInEntry`
returns false. The created basic block has a br jumping to the original entry
block. The new basic block causes the function label line and the other entry
block lines to be covered by different basic blocks, which can affect line
counts with special control flows (fork/exec in the entry block requires
heuristics in llvm-cov gcov to get consistent line counts).
int main() { // BB0
return 0; // BB2 (due to entry block splitting)
}
// BB1 is the exit block (since gcov 4.8)
This patch adds a synthetic entry block (like PGOInstrumentation and GCC) and
inserts an edge from the synthetic entry block to the original entry block. We
can thus remove the tricky `shouldKeepInEntry` and entry block splitting. The
number of basic blocks does not change, but the emitted .gcno files will be
smaller because we can save one GCOV_TAG_LINES tag.
// BB0 is the synthetic entry block with a single edge to BB2
int main() { // BB2
return 0; // BB2
}
// BB1 is the exit block (since gcov 4.8)
This commit is contained in:
Fangrui Song
parent
11352fa83b
commit
dbac20bb6b
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@ -325,16 +325,12 @@ namespace {
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GCOVFunction(GCOVProfiler *P, Function *F, const DISubprogram *SP,
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unsigned EndLine, uint32_t Ident, int Version)
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: GCOVRecord(P), SP(SP), EndLine(EndLine), Ident(Ident),
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Version(Version), ReturnBlock(P, 1) {
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Version(Version), EntryBlock(P, 0), ReturnBlock(P, 1) {
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LLVM_DEBUG(dbgs() << "Function: " << getFunctionName(SP) << "\n");
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bool ExitBlockBeforeBody = Version >= 48;
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uint32_t i = 0;
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for (auto &BB : *F) {
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// Skip index 1 if it's assigned to the ReturnBlock.
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if (i == 1 && ExitBlockBeforeBody)
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++i;
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uint32_t i = ExitBlockBeforeBody ? 2 : 1;
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for (BasicBlock &BB : *F)
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Blocks.insert(std::make_pair(&BB, GCOVBlock(P, i++)));
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}
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if (!ExitBlockBeforeBody)
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ReturnBlock.Number = i;
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@ -349,6 +345,7 @@ namespace {
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return Blocks.find(BB)->second;
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}
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GCOVBlock &getEntryBlock() { return EntryBlock; }
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GCOVBlock &getReturnBlock() {
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return ReturnBlock;
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}
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@ -391,17 +388,22 @@ namespace {
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// Emit count of blocks.
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write(GCOV_TAG_BLOCKS);
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if (Version < 80) {
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write(Blocks.size() + 1);
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for (int i = Blocks.size() + 1; i; --i)
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write(Blocks.size() + 2);
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for (int i = Blocks.size() + 2; i; --i)
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write(0);
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} else {
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write(1);
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write(Blocks.size() + 1);
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write(Blocks.size() + 2);
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}
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LLVM_DEBUG(dbgs() << (Blocks.size() + 1) << " blocks\n");
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// Emit edges between blocks.
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Function *F = Blocks.begin()->first->getParent();
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write(GCOV_TAG_ARCS);
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write(3);
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write(0);
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write(getBlock(&F->getEntryBlock()).Number);
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write(0); // no flags
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for (BasicBlock &I : *F) {
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GCOVBlock &Block = getBlock(&I);
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if (Block.OutEdges.empty()) continue;
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@ -429,6 +431,7 @@ namespace {
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uint32_t FuncChecksum;
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int Version;
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DenseMap<BasicBlock *, GCOVBlock> Blocks;
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GCOVBlock EntryBlock;
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GCOVBlock ReturnBlock;
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};
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}
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@ -604,16 +607,6 @@ static bool isUsingScopeBasedEH(Function &F) {
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return isScopedEHPersonality(Personality);
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}
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static bool shouldKeepInEntry(BasicBlock::iterator It) {
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if (isa<AllocaInst>(*It)) return true;
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if (isa<DbgInfoIntrinsic>(*It)) return true;
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if (auto *II = dyn_cast<IntrinsicInst>(It)) {
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if (II->getIntrinsicID() == llvm::Intrinsic::localescape) return true;
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}
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return false;
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}
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bool GCOVProfiler::AddFlushBeforeForkAndExec() {
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SmallVector<CallInst *, 2> Forks;
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SmallVector<CallInst *, 2> Execs;
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@ -740,10 +733,6 @@ void GCOVProfiler::emitProfileNotes() {
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// gcov expects every function to start with an entry block that has a
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// single successor, so split the entry block to make sure of that.
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BasicBlock &EntryBlock = F.getEntryBlock();
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BasicBlock::iterator It = EntryBlock.begin();
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while (shouldKeepInEntry(It))
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++It;
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EntryBlock.splitBasicBlock(It);
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Funcs.push_back(std::make_unique<GCOVFunction>(this, &F, SP, EndLine,
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FunctionIdent++, Version));
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@ -758,6 +747,7 @@ void GCOVProfiler::emitProfileNotes() {
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if (!SP->isArtificial())
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Func.getBlock(&EntryBlock).getFile(Filename).addLine(Line);
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Func.getEntryBlock().addEdge(Func.getBlock(&EntryBlock));
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for (auto &BB : F) {
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GCOVBlock &Block = Func.getBlock(&BB);
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Instruction *TI = BB.getTerminator();
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@ -846,6 +836,7 @@ bool GCOVProfiler::emitProfileArcs() {
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DenseMap<std::pair<BasicBlock *, BasicBlock *>, unsigned> EdgeToCounter;
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unsigned Edges = 0;
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EdgeToCounter[{nullptr, &F.getEntryBlock()}] = Edges++;
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for (auto &BB : F) {
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Instruction *TI = BB.getTerminator();
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if (isa<ReturnInst>(TI)) {
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@ -869,12 +860,20 @@ bool GCOVProfiler::emitProfileArcs() {
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// If a BB has several predecessors, use a PHINode to select
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// the correct counter.
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for (auto &BB : F) {
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const unsigned EdgeCount =
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std::distance(pred_begin(&BB), pred_end(&BB));
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if (EdgeCount) {
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// The phi node must be at the begin of the BB.
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IRBuilder<> BuilderForPhi(&*BB.begin());
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Type *Int64PtrTy = Type::getInt64PtrTy(*Ctx);
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// The phi node must be at the begin of the BB.
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IRBuilder<> BuilderForPhi(&*BB.begin());
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IRBuilder<> Builder(&*BB.getFirstInsertionPt());
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Type *Int64PtrTy = Type::getInt64PtrTy(*Ctx);
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Value *V;
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if (&BB == &F.getEntryBlock()) {
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auto It = EdgeToCounter.find({nullptr, &BB});
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V = Builder.CreateConstInBoundsGEP2_64(Counters->getValueType(),
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Counters, 0, It->second);
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} else {
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const unsigned EdgeCount =
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std::distance(pred_begin(&BB), pred_end(&BB));
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if (EdgeCount == 0)
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continue;
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PHINode *Phi = BuilderForPhi.CreatePHI(Int64PtrTy, EdgeCount);
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for (BasicBlock *Pred : predecessors(&BB)) {
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auto It = EdgeToCounter.find({Pred, &BB});
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@ -883,36 +882,34 @@ bool GCOVProfiler::emitProfileArcs() {
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Value *EdgeCounter = BuilderForPhi.CreateConstInBoundsGEP2_64(
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Counters->getValueType(), Counters, 0, Edge);
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Phi->addIncoming(EdgeCounter, Pred);
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V = Phi;
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}
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}
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// Skip phis, landingpads.
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IRBuilder<> Builder(&*BB.getFirstInsertionPt());
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if (Options.Atomic) {
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Builder.CreateAtomicRMW(AtomicRMWInst::Add, V, Builder.getInt64(1),
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AtomicOrdering::Monotonic);
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} else {
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Value *Count = Builder.CreateLoad(Builder.getInt64Ty(), V);
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Count = Builder.CreateAdd(Count, Builder.getInt64(1));
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Builder.CreateStore(Count, V);
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}
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Instruction *TI = BB.getTerminator();
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if (isa<ReturnInst>(TI)) {
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auto It = EdgeToCounter.find({&BB, nullptr});
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assert(It != EdgeToCounter.end());
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const unsigned Edge = It->second;
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Value *Counter = Builder.CreateConstInBoundsGEP2_64(
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Counters->getValueType(), Counters, 0, Edge);
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if (Options.Atomic) {
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Builder.CreateAtomicRMW(AtomicRMWInst::Add, Phi,
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Builder.CreateAtomicRMW(AtomicRMWInst::Add, Counter,
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Builder.getInt64(1),
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AtomicOrdering::Monotonic);
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} else {
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Value *Count = Builder.CreateLoad(Builder.getInt64Ty(), Phi);
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Value *Count = Builder.CreateLoad(Builder.getInt64Ty(), Counter);
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Count = Builder.CreateAdd(Count, Builder.getInt64(1));
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Builder.CreateStore(Count, Phi);
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}
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Instruction *TI = BB.getTerminator();
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if (isa<ReturnInst>(TI)) {
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auto It = EdgeToCounter.find({&BB, nullptr});
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assert(It != EdgeToCounter.end());
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const unsigned Edge = It->second;
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Value *Counter = Builder.CreateConstInBoundsGEP2_64(
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Counters->getValueType(), Counters, 0, Edge);
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if (Options.Atomic) {
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Builder.CreateAtomicRMW(AtomicRMWInst::Add, Counter,
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Builder.getInt64(1),
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AtomicOrdering::Monotonic);
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} else {
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Value *Count = Builder.CreateLoad(Builder.getInt64Ty(), Counter);
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Count = Builder.CreateAdd(Count, Builder.getInt64(1));
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Builder.CreateStore(Count, Counter);
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}
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Builder.CreateStore(Count, Counter);
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}
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}
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}
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@ -4,12 +4,8 @@
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; CHECK-LABEL: void @empty()
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; CHECK-NEXT: entry:
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; CHECK-NEXT: br label %0, !dbg [[DBG:![0-9]+]]
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; CHECK: 0:
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; CHECK-NEXT: %1 = phi i64* [ getelementptr inbounds ([2 x i64], [2 x i64]* @__llvm_gcov_ctr, i64 0, i64 0), %entry ], !dbg [[DBG]]
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; CHECK-NEXT: %2 = atomicrmw add i64* %1, i64 1 monotonic, !dbg [[DBG]]
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;; Counter for the exit.
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; CHECK-NEXT: %3 = atomicrmw add i64* getelementptr inbounds ([2 x i64], [2 x i64]* @__llvm_gcov_ctr, i64 0, i64 1), i64 1 monotonic, !dbg [[DBG]]
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; CHECK-NEXT: %0 = atomicrmw add i64* getelementptr inbounds ([2 x i64], [2 x i64]* @__llvm_gcov_ctr, i64 0, i64 0), i64 1 monotonic, !dbg [[DBG:![0-9]+]]
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; CHECK-NEXT: %1 = atomicrmw add i64* getelementptr inbounds ([2 x i64], [2 x i64]* @__llvm_gcov_ctr, i64 0, i64 1), i64 1 monotonic, !dbg [[DBG]]
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; CHECK-NEXT: ret void, !dbg [[DBG]]
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define dso_local void @empty() !dbg !5 {
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