[MachinePipeliner] Add a way to unit-test the schedule emitter

Emitting a schedule is really hard. There are lots of corner cases to take care of; in fact, of the 60+ SWP-specific testcases in the Hexagon backend most of those are testing codegen rather than the schedule creation itself.

One issue is that to test an emission corner case we must craft an input such that the generated schedule uses that corner case; sometimes this is very hard and convolutes testcases. Other times it is impossible but we want to test it anyway.

This patch adds a simple test pass that will consume a module containing a loop and generate pipelined code from it. We use post-instr-symbols as a way to annotate instructions with the stage and cycle that we want to schedule them at.

We also provide a flag that causes the MachinePipeliner to generate these annotations instead of actually emitting code; this allows us to generate an input testcase with:

  llc < %s -stop-after=pipeliner -pipeliner-annotate-for-testing -o test.mir

And run the emission in isolation with:

  llc < test.mir -run-pass=modulo-schedule-test

llvm-svn: 370705

3 files changed, 128 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/CodeGen.cpp b/llvm/lib/CodeGen/CodeGen.cpp
index c6376290dab..51be4e3af01 100644
--- a/llvm/lib/CodeGen/CodeGen.cpp
+++ b/llvm/lib/CodeGen/CodeGen.cpp
@@ -68,6 +68,7 @@ void llvm::initializeCodeGen(PassRegistry &Registry) {
   initializeMachineOptimizationRemarkEmitterPassPass(Registry);
   initializeMachineOutlinerPass(Registry);
   initializeMachinePipelinerPass(Registry);
+  initializeModuloScheduleTestPass(Registry);
   initializeMachinePostDominatorTreePass(Registry);
   initializeMachineRegionInfoPassPass(Registry);
   initializeMachineSchedulerPass(Registry);
diff --git a/llvm/lib/CodeGen/MachinePipeliner.cpp b/llvm/lib/CodeGen/MachinePipeliner.cpp
index b138342c784..ff3d2feab5e 100644
--- a/llvm/lib/CodeGen/MachinePipeliner.cpp
+++ b/llvm/lib/CodeGen/MachinePipeliner.cpp
@@ -154,6 +154,12 @@ static cl::opt<bool> SwpShowResMask("pipeliner-show-mask", cl::Hidden,
 static cl::opt<bool> SwpDebugResource("pipeliner-dbg-res", cl::Hidden,
                                       cl::init(false));
 
+static cl::opt<bool> EmitTestAnnotations(
+    "pipeliner-annotate-for-testing", cl::Hidden, cl::init(false),
+    cl::desc("Instead of emitting the pipelined code, annotate instructions "
+             "with the generated schedule for feeding into the "
+             "-modulo-schedule-test pass"));
+
 namespace llvm {
 
 // A command line option to enable the CopyToPhi DAG mutation.
@@ -536,6 +542,13 @@ void SwingSchedulerDAG::schedule() {
 
   ModuloSchedule MS(MF, &Loop, std::move(OrderedInsts), std::move(Cycles),
                     std::move(Stages));
+  if (EmitTestAnnotations) {
+    assert(NewInstrChanges.empty() &&
+           "Cannot serialize a schedule with InstrChanges!");
+    ModuloScheduleTestAnnotater MSTI(MF, MS);
+    MSTI.annotate();
+    return;
+  }
   ModuloScheduleExpander MSE(MF, MS, LIS, std::move(NewInstrChanges));
   MSE.expand();
   ++NumPipelined;
diff --git a/llvm/lib/CodeGen/ModuloSchedule.cpp b/llvm/lib/CodeGen/ModuloSchedule.cpp
index 703d7926a69..80b022e232f 100644
--- a/llvm/lib/CodeGen/ModuloSchedule.cpp
+++ b/llvm/lib/CodeGen/ModuloSchedule.cpp
@@ -7,14 +7,21 @@
 //===----------------------------------------------------------------------===//
 
 #include "llvm/CodeGen/ModuloSchedule.h"
+#include "llvm/Support/raw_ostream.h"
+#include "llvm/ADT/StringExtras.h"
 #include "llvm/CodeGen/LiveIntervals.h"
 #include "llvm/CodeGen/MachineInstrBuilder.h"
 #include "llvm/CodeGen/TargetInstrInfo.h"
+#include "llvm/MC/MCContext.h"
 #include "llvm/Support/Debug.h"
 
 #define DEBUG_TYPE "pipeliner"
 using namespace llvm;
 
+//===----------------------------------------------------------------------===//
+// ModuloScheduleExpander implementation
+//===----------------------------------------------------------------------===//
+
 /// Return the register values for  the operands of a Phi instruction.
 /// This function assume the instruction is a Phi.
 static void getPhiRegs(MachineInstr &Phi, MachineBasicBlock *Loop,
@@ -1188,3 +1195,110 @@ bool ModuloScheduleExpander::isLoopCarried(MachineInstr &Phi) {
   int LoopStage = Schedule.getStage(Use);
   return (LoopCycle > DefCycle) || (LoopStage <= DefStage);
 }
+
+//===----------------------------------------------------------------------===//
+// ModuloScheduleTestPass implementation
+//===----------------------------------------------------------------------===//
+// This pass constructs a ModuloSchedule from its module and runs
+// ModuloScheduleExpander.
+//
+// The module is expected to contain a single-block analyzable loop.
+// The total order of instructions is taken from the loop as-is.
+// Instructions are expected to be annotated with a PostInstrSymbol.
+// This PostInstrSymbol must have the following format:
+//  "Stage=%d Cycle=%d".
+//===----------------------------------------------------------------------===//
+
+class ModuloScheduleTest : public MachineFunctionPass {
+public:
+  static char ID;
+
+  ModuloScheduleTest() : MachineFunctionPass(ID) {
+    initializeModuloScheduleTestPass(*PassRegistry::getPassRegistry());
+  }
+
+  bool runOnMachineFunction(MachineFunction &MF) override;
+  void runOnLoop(MachineFunction &MF, MachineLoop &L);
+
+  void getAnalysisUsage(AnalysisUsage &AU) const override {
+    AU.addRequired<MachineLoopInfo>();
+    AU.addRequired<LiveIntervals>();
+    MachineFunctionPass::getAnalysisUsage(AU);
+  }
+};
+
+char ModuloScheduleTest::ID = 0;
+
+INITIALIZE_PASS_BEGIN(ModuloScheduleTest, "modulo-schedule-test",
+                      "Modulo Schedule test pass", false, false)
+INITIALIZE_PASS_DEPENDENCY(MachineLoopInfo)
+INITIALIZE_PASS_DEPENDENCY(LiveIntervals)
+INITIALIZE_PASS_END(ModuloScheduleTest, "modulo-schedule-test",
+                    "Modulo Schedule test pass", false, false)
+
+bool ModuloScheduleTest::runOnMachineFunction(MachineFunction &MF) {
+  MachineLoopInfo &MLI = getAnalysis<MachineLoopInfo>();
+  for (auto *L : MLI) {
+    if (L->getTopBlock() != L->getBottomBlock())
+      continue;
+    runOnLoop(MF, *L);
+    return false;
+  }
+  return false;
+}
+
+static void parseSymbolString(StringRef S, int &Cycle, int &Stage) {
+  std::pair<StringRef, StringRef> StageAndCycle = getToken(S, "_");
+  std::pair<StringRef, StringRef> StageTokenAndValue =
+      getToken(StageAndCycle.first, "-");
+  std::pair<StringRef, StringRef> CycleTokenAndValue =
+      getToken(StageAndCycle.second, "-");
+  if (StageTokenAndValue.first != "Stage" ||
+      CycleTokenAndValue.first != "_Cycle") {
+    llvm_unreachable(
+        "Bad post-instr symbol syntax: see comment in ModuloScheduleTest");
+    return;
+  }
+
+  StageTokenAndValue.second.drop_front().getAsInteger(10, Stage);
+  CycleTokenAndValue.second.drop_front().getAsInteger(10, Cycle);
+
+  dbgs() << "  Stage=" << Stage << ", Cycle=" << Cycle << "\n";
+}
+
+void ModuloScheduleTest::runOnLoop(MachineFunction &MF, MachineLoop &L) {
+  LiveIntervals &LIS = getAnalysis<LiveIntervals>();
+  MachineBasicBlock *BB = L.getTopBlock();
+  dbgs() << "--- ModuloScheduleTest running on BB#" << BB->getNumber() << "\n";
+
+  DenseMap<MachineInstr *, int> Cycle, Stage;
+  std::vector<MachineInstr *> Instrs;
+  for (MachineInstr &MI : *BB) {
+    if (MI.isTerminator())
+      continue;
+    Instrs.push_back(&MI);
+    if (MCSymbol *Sym = MI.getPostInstrSymbol()) {
+      dbgs() << "Parsing post-instr symbol for " << MI;
+      parseSymbolString(Sym->getName(), Cycle[&MI], Stage[&MI]);
+    }
+  }
+
+  ModuloSchedule MS(MF, &L, std::move(Instrs), std::move(Cycle), std::move(Stage));
+  ModuloScheduleExpander MSE(
+      MF, MS, LIS, /*InstrChanges=*/ModuloScheduleExpander::InstrChangesTy());
+  MSE.expand();
+}
+
+//===----------------------------------------------------------------------===//
+// ModuloScheduleTestAnnotater implementation
+//===----------------------------------------------------------------------===//
+
+void ModuloScheduleTestAnnotater::annotate() {
+  for (MachineInstr *MI : S.getInstructions()) {
+    SmallVector<char, 16> SV;
+    raw_svector_ostream OS(SV);
+    OS << "Stage-" << S.getStage(MI) << "_Cycle-" << S.getCycle(MI);
+    MCSymbol *Sym = MF.getContext().getOrCreateSymbol(OS.str());
+    MI->setPostInstrSymbol(MF, Sym);
+  }
+}