/// \brief Assign DWARF discriminators.
///
/// To assign discriminators, we examine the boundaries of every
/// basic block and its successors. Suppose there is a basic block B1
/// with successor B2. The last instruction I1 in B1 and the first
/// instruction I2 in B2 are located at the same file and line number.
/// This situation is illustrated in the following code snippet:
///
/// if (i < 10) x = i;
///
/// entry:
/// br i1 %cmp, label %if.then, label %if.end, !dbg !10
/// if.then:
/// %1 = load i32* %i.addr, align 4, !dbg !10
/// store i32 %1, i32* %x, align 4, !dbg !10
/// br label %if.end, !dbg !10
/// if.end:
/// ret void, !dbg !12
///
/// Notice how the branch instruction in block 'entry' and all the
/// instructions in block 'if.then' have the exact same debug location
/// information (!dbg !10).
///
/// To distinguish instructions in block 'entry' from instructions in
/// block 'if.then', we generate a new lexical block for all the
/// instruction in block 'if.then' that share the same file and line
/// location with the last instruction of block 'entry'.
///
/// This new lexical block will have the same location information as
/// the previous one, but with a new DWARF discriminator value.
///
/// One of the main uses of this discriminator value is in runtime
/// sample profilers. It allows the profiler to distinguish instructions
/// at location !dbg !10 that execute on different basic blocks. This is
/// important because while the predicate 'if (x < 10)' may have been
/// executed millions of times, the assignment 'x = i' may have only
/// executed a handful of times (meaning that the entry->if.then edge is
/// seldom taken).
///
/// If we did not have discriminator information, the profiler would
/// assign the same weight to both blocks 'entry' and 'if.then', which
/// in turn will make it conclude that the entry->if.then edge is very
/// hot.
///
/// To decide where to create new discriminator values, this function
/// traverses the CFG and examines instruction at basic block boundaries.
/// If the last instruction I1 of a block B1 is at the same file and line
/// location as instruction I2 of successor B2, then it creates a new
/// lexical block for I2 and all the instruction in B2 that share the same
/// file and line location as I2. This new lexical block will have a
/// different discriminator number than I1.
bool AddDiscriminators::runOnFunction(Function &F) {
// If the function has debug information, but the user has disabled
// discriminators, do nothing.
// Simlarly, if the function has no debug info, do nothing.
// Finally, if this module is built with dwarf versions earlier than 4,
// do nothing (discriminator support is a DWARF 4 feature).
if (NoDiscriminators || !hasDebugInfo(F) ||
F.getParent()->getDwarfVersion() < 4)
return false;
bool Changed = false;
Module *M = F.getParent();
LLVMContext &Ctx = M->getContext();
DIBuilder Builder(*M, /*AllowUnresolved*/ false);
typedef std::pair<StringRef, unsigned> Location;
typedef DenseMap<const BasicBlock *, Metadata *> BBScopeMap;
typedef DenseMap<Location, BBScopeMap> LocationBBMap;
typedef DenseMap<Location, unsigned> LocationDiscriminatorMap;
LocationBBMap LBM;
LocationDiscriminatorMap LDM;
// Traverse all instructions in the function. If the source line location
// of the instruction appears in other basic block, assign a new
// discriminator for this instruction.
for (BasicBlock &B : F) {
for (auto &I : B.getInstList()) {
if (isa<DbgInfoIntrinsic>(&I))
continue;
const DILocation *DIL = I.getDebugLoc();
if (!DIL)
continue;
Location L = std::make_pair(DIL->getFilename(), DIL->getLine());
auto &BBMap = LBM[L];
auto R = BBMap.insert(std::make_pair(&B, (Metadata *)nullptr));
if (BBMap.size() == 1)
continue;
bool InsertSuccess = R.second;
Metadata *&NewScope = R.first->second;
// If we could insert a different block in the same location, a
// discriminator is needed to distinguish both instructions.
if (InsertSuccess) {
auto *Scope = DIL->getScope();
auto *File =
Builder.createFile(DIL->getFilename(), Scope->getDirectory());
NewScope = Builder.createLexicalBlockFile(Scope, File, ++LDM[L]);
}
I.setDebugLoc(DILocation::get(Ctx, DIL->getLine(), DIL->getColumn(),
NewScope, DIL->getInlinedAt()));
DEBUG(dbgs() << DIL->getFilename() << ":" << DIL->getLine() << ":"
<< DIL->getColumn() << ":"
<< dyn_cast<DILexicalBlockFile>(NewScope)->getDiscriminator()
<< I << "\n");
Changed = true;
}
}
// Traverse all instructions and assign new discriminators to call
// instructions with the same lineno that are in the same basic block.
// Sample base profile needs to distinguish different function calls within
// a same source line for correct profile annotation.
for (BasicBlock &B : F) {
const DILocation *FirstDIL = nullptr;
for (auto &I : B.getInstList()) {
CallInst *Current = dyn_cast<CallInst>(&I);
if (!Current || isa<DbgInfoIntrinsic>(&I))
continue;
DILocation *CurrentDIL = Current->getDebugLoc();
if (FirstDIL) {
if (CurrentDIL && CurrentDIL->getLine() == FirstDIL->getLine() &&
CurrentDIL->getFilename() == FirstDIL->getFilename()) {
auto *Scope = FirstDIL->getScope();
auto *File = Builder.createFile(FirstDIL->getFilename(),
Scope->getDirectory());
Location L =
std::make_pair(FirstDIL->getFilename(), FirstDIL->getLine());
auto *NewScope =
Builder.createLexicalBlockFile(Scope, File, ++LDM[L]);
Current->setDebugLoc(DILocation::get(
Ctx, CurrentDIL->getLine(), CurrentDIL->getColumn(), NewScope,
CurrentDIL->getInlinedAt()));
Changed = true;
} else {
FirstDIL = CurrentDIL;
}
} else {
FirstDIL = CurrentDIL;
}
}
}
return Changed;
}
static bool markTails(Function &F, bool &AllCallsAreTailCalls) {
if (F.callsFunctionThatReturnsTwice())
return false;
AllCallsAreTailCalls = true;
// The local stack holds all alloca instructions and all byval arguments.
AllocaDerivedValueTracker Tracker;
for (Argument &Arg : F.args()) {
if (Arg.hasByValAttr())
Tracker.walk(&Arg);
}
for (auto &BB : F) {
for (auto &I : BB)
if (AllocaInst *AI = dyn_cast<AllocaInst>(&I))
Tracker.walk(AI);
}
bool Modified = false;
// Track whether a block is reachable after an alloca has escaped. Blocks that
// contain the escaping instruction will be marked as being visited without an
// escaped alloca, since that is how the block began.
enum VisitType {
UNVISITED,
UNESCAPED,
ESCAPED
};
DenseMap<BasicBlock *, VisitType> Visited;
// We propagate the fact that an alloca has escaped from block to successor.
// Visit the blocks that are propagating the escapedness first. To do this, we
// maintain two worklists.
SmallVector<BasicBlock *, 32> WorklistUnescaped, WorklistEscaped;
// We may enter a block and visit it thinking that no alloca has escaped yet,
// then see an escape point and go back around a loop edge and come back to
// the same block twice. Because of this, we defer setting tail on calls when
// we first encounter them in a block. Every entry in this list does not
// statically use an alloca via use-def chain analysis, but may find an alloca
// through other means if the block turns out to be reachable after an escape
// point.
SmallVector<CallInst *, 32> DeferredTails;
BasicBlock *BB = &F.getEntryBlock();
VisitType Escaped = UNESCAPED;
do {
for (auto &I : *BB) {
if (Tracker.EscapePoints.count(&I))
Escaped = ESCAPED;
CallInst *CI = dyn_cast<CallInst>(&I);
if (!CI || CI->isTailCall())
continue;
bool IsNoTail = CI->isNoTailCall() || CI->hasOperandBundles();
if (!IsNoTail && CI->doesNotAccessMemory()) {
// A call to a readnone function whose arguments are all things computed
// outside this function can be marked tail. Even if you stored the
// alloca address into a global, a readnone function can't load the
// global anyhow.
//
// Note that this runs whether we know an alloca has escaped or not. If
// it has, then we can't trust Tracker.AllocaUsers to be accurate.
bool SafeToTail = true;
for (auto &Arg : CI->arg_operands()) {
if (isa<Constant>(Arg.getUser()))
continue;
if (Argument *A = dyn_cast<Argument>(Arg.getUser()))
if (!A->hasByValAttr())
continue;
SafeToTail = false;
break;
}
if (SafeToTail) {
emitOptimizationRemark(
F.getContext(), "tailcallelim", F, CI->getDebugLoc(),
"marked this readnone call a tail call candidate");
CI->setTailCall();
Modified = true;
continue;
}
}
if (!IsNoTail && Escaped == UNESCAPED && !Tracker.AllocaUsers.count(CI)) {
DeferredTails.push_back(CI);
} else {
AllCallsAreTailCalls = false;
}
}
for (auto *SuccBB : make_range(succ_begin(BB), succ_end(BB))) {
auto &State = Visited[SuccBB];
if (State < Escaped) {
State = Escaped;
if (State == ESCAPED)
WorklistEscaped.push_back(SuccBB);
else
WorklistUnescaped.push_back(SuccBB);
}
}
if (!WorklistEscaped.empty()) {
BB = WorklistEscaped.pop_back_val();
Escaped = ESCAPED;
} else {
BB = nullptr;
while (!WorklistUnescaped.empty()) {
auto *NextBB = WorklistUnescaped.pop_back_val();
if (Visited[NextBB] == UNESCAPED) {
BB = NextBB;
Escaped = UNESCAPED;
break;
}
}
}
} while (BB);
for (CallInst *CI : DeferredTails) {
if (Visited[CI->getParent()] != ESCAPED) {
// If the escape point was part way through the block, calls after the
// escape point wouldn't have been put into DeferredTails.
emitOptimizationRemark(F.getContext(), "tailcallelim", F,
CI->getDebugLoc(),
"marked this call a tail call candidate");
CI->setTailCall();
Modified = true;
} else {
AllCallsAreTailCalls = false;
}
}
return Modified;
}
int compile(list<string> args, list<string> kgen_args,
string merge, list<string> merge_args,
string input, string output, int arch,
string host_compiler, string fileprefix)
{
//
// The LLVM compiler to emit IR.
//
const char* llvm_compiler = "kernelgen-gfortran";
//
// Interpret kernelgen compile options.
//
for (list<string>::iterator iarg = kgen_args.begin(),
iearg = kgen_args.end(); iarg != iearg; iarg++)
{
const char* arg = (*iarg).c_str();
if (!strncmp(arg, "-Wk,--llvm-compiler=", 20))
llvm_compiler = arg + 20;
}
//
// Generate temporary output file.
// Check if output file is specified in the command line.
// Replace or add output to the temporary file.
//
cfiledesc tmp_output = cfiledesc::mktemp(fileprefix);
bool output_specified = false;
for (list<string>::iterator iarg = args.begin(),
iearg = args.end(); iarg != iearg; iarg++)
{
const char* arg = (*iarg).c_str();
if (!strcmp(arg, "-o"))
{
iarg++;
*iarg = tmp_output.getFilename();
output_specified = true;
break;
}
}
if (!output_specified)
{
args.push_back("-o");
args.push_back(tmp_output.getFilename());
}
//
// 1) Compile source code using regular host compiler.
//
{
if (verbose)
{
cout << host_compiler;
for (list<string>::iterator iarg = args.begin(),
iearg = args.end(); iarg != iearg; iarg++)
cout << " " << *iarg;
cout << endl;
}
int status = execute(host_compiler, args, "", NULL, NULL);
if (status) return status;
}
//
// 2) Emit LLVM IR.
//
string out = "";
{
list<string> emit_ir_args;
for (list<string>::iterator iarg = args.begin(),
iearg = args.end(); iarg != iearg; iarg++)
{
const char* arg = (*iarg).c_str();
if (!strcmp(arg, "-c") || !strcmp(arg, "-o"))
{
iarg++;
continue;
}
if (!strcmp(arg, "-g"))
{
continue;
}
emit_ir_args.push_back(*iarg);
}
emit_ir_args.push_back("-fplugin=/opt/kernelgen/lib/dragonegg.so");
emit_ir_args.push_back("-fplugin-arg-dragonegg-emit-ir");
emit_ir_args.push_back("-S");
emit_ir_args.push_back(input);
emit_ir_args.push_back("-o");
emit_ir_args.push_back("-");
if (verbose)
{
cout << llvm_compiler;
for (list<string>::iterator iarg = emit_ir_args.begin(),
iearg = emit_ir_args.end(); iarg != iearg; iarg++)
cout << " " << *iarg;
cout << endl;
}
int status = execute(llvm_compiler, emit_ir_args, "", &out, NULL);
if (status) return status;
}
//
// 3) Record existing module functions.
//
LLVMContext &context = getGlobalContext();
SMDiagnostic diag;
MemoryBuffer* buffer1 = MemoryBuffer::getMemBuffer(out);
auto_ptr<Module> m1;
m1.reset(ParseIR(buffer1, diag, context));
//m1.get()->dump();
//
// 4) Inline calls and extract loops into new functions.
//
MemoryBuffer* buffer2 = MemoryBuffer::getMemBuffer(out);
auto_ptr<Module> m2;
m2.reset(ParseIR(buffer2, diag, context));
{
PassManager manager;
manager.add(createInstructionCombiningPass());
manager.run(*m2.get());
}
std::vector<CallInst *> LoopFuctionCalls;
{
PassManager manager;
manager.add(createBranchedLoopExtractorPass(LoopFuctionCalls));
manager.run(*m2.get());
}
//m2.get()->dump();
//
// 5) Replace call to loop functions with call to launcher.
// Append "always inline" attribute to all other functions.
//
Type* int32Ty = Type::getInt32Ty(context);
Function* launch = Function::Create(
TypeBuilder<types::i<32>(types::i<8>*, types::i<64>, types::i<32>*), true>::get(context),
GlobalValue::ExternalLinkage, "kernelgen_launch", m2.get());
for (Module::iterator f1 = m2.get()->begin(), fe1 = m2.get()->end(); f1 != fe1; f1++)
{
Function* func = f1;
if (func->isDeclaration()) continue;
// Search for the current function in original module
// functions list.
// If function is not in list of original module, then
// it is generated by the loop extractor.
// Append "always inline" attribute to all other functions.
if (m1.get()->getFunction(func->getName()))
{
const AttrListPtr attr = func->getAttributes();
const AttrListPtr attr_new = attr.addAttr(~0U, Attribute::AlwaysInline);
func->setAttributes(attr_new);
continue;
}
// Each such function must be extracted to the
// standalone module and packed into resulting
// object file data section.
if (verbose)
cout << "Preparing loop function " << func->getName().data() <<
" ..." << endl;
// Reset to default visibility.
func->setVisibility(GlobalValue::DefaultVisibility);
// Reset to default linkage.
func->setLinkage(GlobalValue::ExternalLinkage);
// Replace call to this function in module with call to launcher.
bool found = false;
for (Module::iterator f2 = m2->begin(), fe2 = m2->end(); (f2 != fe2) && !found; f2++)
for (Function::iterator bb = f2->begin(); (bb != f2->end()) && !found; bb++)
for (BasicBlock::iterator i = bb->begin(); i != bb->end(); i++)
{
// Check if instruction in focus is a call.
CallInst* call = dyn_cast<CallInst>(cast<Value>(i));
if (!call) continue;
// Check if function is called (needs -instcombine pass).
Function* callee = call->getCalledFunction();
if (!callee) continue;
if (callee->isDeclaration()) continue;
if (callee->getName() != func->getName()) continue;
// Create a constant array holding original called
// function name.
Constant* name = ConstantArray::get(
context, callee->getName(), true);
// Create and initialize the memory buffer for name.
ArrayType* nameTy = cast<ArrayType>(name->getType());
AllocaInst* nameAlloc = new AllocaInst(nameTy, "", call);
StoreInst* nameInit = new StoreInst(name, nameAlloc, "", call);
Value* Idx[2];
Idx[0] = Constant::getNullValue(Type::getInt32Ty(context));
Idx[1] = ConstantInt::get(Type::getInt32Ty(context), 0);
GetElementPtrInst* namePtr = GetElementPtrInst::Create(nameAlloc, Idx, "", call);
// Add pointer to the original function string name.
SmallVector<Value*, 16> call_args;
call_args.push_back(namePtr);
// Add size of the aggregated arguments structure.
{
BitCastInst* BC = new BitCastInst(
call->getArgOperand(0), Type::getInt64PtrTy(context),
"", call);
LoadInst* LI = new LoadInst(BC, "", call);
call_args.push_back(LI);
}
// Add original aggregated structure argument.
call_args.push_back(call->getArgOperand(0));
// Create new function call with new call arguments
// and copy old call properties.
CallInst* newcall = CallInst::Create(launch, call_args, "", call);
//newcall->takeName(call);
newcall->setCallingConv(call->getCallingConv());
newcall->setAttributes(call->getAttributes());
newcall->setDebugLoc(call->getDebugLoc());
// Replace old call with new one.
call->replaceAllUsesWith(newcall);
call->eraseFromParent();
found = true;
break;
}
}
//m2.get()->dump();
//
// 6) Apply optimization passes to the resulting common
// module.
//
{
PassManager manager;
manager.add(createLowerSetJmpPass());
PassManagerBuilder builder;
builder.Inliner = createFunctionInliningPass();
builder.OptLevel = 3;
builder.DisableSimplifyLibCalls = true;
builder.populateModulePassManager(manager);
manager.run(*m2.get());
}
//m2.get()->dump();
//
// 7) Embed the resulting module into object file.
//
{
string ir_string;
raw_string_ostream ir(ir_string);
ir << (*m2.get());
celf e(tmp_output.getFilename(), output);
e.getSection(".data")->addSymbol(
"__kernelgen_" + string(input),
ir_string.c_str(), ir_string.size() + 1);
}
return 0;
}
