Remove MachineLoopInfo dependency from AsmPrinter.

[mzolotukhin]

Summary

Currently MachineLoopInfo is used in only two places:

1. for computing IsBasicBlockInsideInnermostLoop field of MCCodePaddingContext, and it is never used.
2. in emitBasicBlockLoopComments, which is called only if isVerbose() is true.

Despite that, we currently have a dependency on MachineLoopInfo, which makes
pass manager to compute it and MachineDominator Tree. This patch removes the
use (1) and makes the use (2) lazy, thus avoiding some redundant
recomputations.

[mzolotukhin]

Ping!

[mzolotukhin]

• Don't recompute MLI and MDT on visit of every basic block.
• Rebase.

[rengolin]

llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp

2752

Wait, isn't this only set if isVerbose?

[mzolotukhin]

llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp

2752

Yes, and here it's also under this condition. Am I missing something?

[rengolin]

I had seen the first version of this patch and thought it confusing, so refrained from reviewing (too broad context), but this version is much clearer now, and I can see it as straightforward benefit.

I'll tentatively approve waiting for another review for a day or so?

Thanks!

llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp

2752

D'oh! Sorry, it is. Late night patch review.

[mzolotukhin]

Thanks, Renato! I'll wait a little to give other reviewers more time to take a look.

Michael

llvm/include/llvm/CodeGen/AsmPrinter.h

public:
   MCContext &OutContext;
 
   /// This is the MCStreamer object for the file we are generating. This
   /// contains the transient state for the current translation unit that we are
   /// generating (such as the current section etc).
   std::unique_ptr<MCStreamer> OutStreamer;
 
   /// The current machine function.
-  const MachineFunction *MF = nullptr;
+  MachineFunction *MF = nullptr;
 
   /// This is a pointer to the current MachineModuleInfo.
   MachineModuleInfo *MMI = nullptr;
 
   /// Optimization remark emitter.
   MachineOptimizationRemarkEmitter *ORE;
 
   /// The symbol for the current function. This is recalculated at the beginning
private:
   // The garbage collection metadata printer table.
   void *GCMetadataPrinters = nullptr; // Really a DenseMap.
 
   /// Emit comments in assembly output if this is true.
   bool VerboseAsm;
 
   static char ID;
 
-  /// If VerboseAsm is set, a pointer to the loop info for this function.
-  MachineLoopInfo *LI = nullptr;
-
   struct HandlerInfo {
     AsmPrinterHandler *Handler;
     const char *TimerName;
     const char *TimerDescription;
     const char *TimerGroupName;
     const char *TimerGroupDescription;
 
     HandlerInfo(AsmPrinterHandler *Handler, const char *TimerName,

llvm/include/llvm/MC/MCCodePadder.h

 class MCInst;
 class MCObjectStreamer;
 class MCSection;
 
 typedef SmallVector<const MCPaddingFragment *, 8> MCPFRange;
 
 struct MCCodePaddingContext {
   bool IsPaddingActive;
-  bool IsBasicBlockInsideInnermostLoop;
   bool IsBasicBlockReachableViaFallthrough;
   bool IsBasicBlockReachableViaBranch;
 };
 
 /// Target-independent base class incharge of all code padding decisions for a
 /// target. During encoding it determines if and where MCPaddingFragments will
 /// be located, as later on, when layout information is available, it determines
 /// their sizes.

llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp

 #include "llvm/Analysis/OptimizationRemarkEmitter.h"
 #include "llvm/BinaryFormat/Dwarf.h"
 #include "llvm/BinaryFormat/ELF.h"
 #include "llvm/CodeGen/GCMetadata.h"
 #include "llvm/CodeGen/GCMetadataPrinter.h"
 #include "llvm/CodeGen/GCStrategy.h"
 #include "llvm/CodeGen/MachineBasicBlock.h"
 #include "llvm/CodeGen/MachineConstantPool.h"
+#include "llvm/CodeGen/MachineDominators.h"
 #include "llvm/CodeGen/MachineFrameInfo.h"
 #include "llvm/CodeGen/MachineFunction.h"
 #include "llvm/CodeGen/MachineFunctionPass.h"
 #include "llvm/CodeGen/MachineInstr.h"
 #include "llvm/CodeGen/MachineInstrBundle.h"
 #include "llvm/CodeGen/MachineJumpTableInfo.h"
 #include "llvm/CodeGen/MachineLoopInfo.h"
 #include "llvm/CodeGen/MachineMemOperand.h"

 }
 
 void AsmPrinter::getAnalysisUsage(AnalysisUsage &AU) const {
   AU.setPreservesAll();
   MachineFunctionPass::getAnalysisUsage(AU);
   AU.addRequired<MachineModuleInfo>();
   AU.addRequired<MachineOptimizationRemarkEmitterPass>();
   AU.addRequired<GCModuleInfo>();
-  AU.addRequired<MachineLoopInfo>();
 }
 
 bool AsmPrinter::doInitialization(Module &M) {
   MMI = getAnalysisIfAvailable<MachineModuleInfo>();
 
   // Initialize TargetLoweringObjectFile.
   const_cast<TargetLoweringObjectFile&>(getObjFileLowering())
     .Initialize(OutContext, TM);
void AsmPrinter::SetupMachineFunction(MachineFunction &MF) {
   bool NeedsLocalForSize = MAI->needsLocalForSize();
   if (needFuncLabelsForEHOrDebugInfo(MF, MMI) || NeedsLocalForSize) {
     CurrentFnBegin = createTempSymbol("func_begin");
     if (NeedsLocalForSize)
       CurrentFnSymForSize = CurrentFnBegin;
   }
 
   ORE = &getAnalysis<MachineOptimizationRemarkEmitterPass>().getORE();
-  LI = &getAnalysis<MachineLoopInfo>();
 
   const TargetSubtargetInfo &STI = MF.getSubtarget();
   EnablePrintSchedInfo = PrintSchedule.getNumOccurrences()
                              ? PrintSchedule
                              : STI.supportPrintSchedInfo();
 }
 
 namespace {
static void emitBasicBlockLoopComments(const MachineBasicBlock &MBB,
   OS << "Loop Header: Depth=" + Twine(Loop->getLoopDepth()) << '\n';
 
   PrintChildLoopComment(OS, Loop, AP.getFunctionNumber());
 }
 
 void AsmPrinter::setupCodePaddingContext(const MachineBasicBlock &MBB,
                                          MCCodePaddingContext &Context) const {
   assert(MF != nullptr && "Machine function must be valid");
-  assert(LI != nullptr && "Loop info must be valid");
   Context.IsPaddingActive = !MF->hasInlineAsm() &&
                             !MF->getFunction().optForSize() &&
                             TM.getOptLevel() != CodeGenOpt::None;
-  const MachineLoop *CurrentLoop = LI->getLoopFor(&MBB);
-  Context.IsBasicBlockInsideInnermostLoop =
-      CurrentLoop != nullptr && CurrentLoop->getSubLoops().empty();
   Context.IsBasicBlockReachableViaFallthrough =
       std::find(MBB.pred_begin(), MBB.pred_end(), MBB.getPrevNode()) !=
       MBB.pred_end();
   Context.IsBasicBlockReachableViaBranch =
       MBB.pred_size() > 0 && !isBlockOnlyReachableByFallthrough(&MBB);
 }
 
 /// EmitBasicBlockStart - This method prints the label for the specified
void AsmPrinter::EmitBasicBlockStart(const MachineBasicBlock &MBB) const {
   if (isVerbose()) {
     if (const BasicBlock *BB = MBB.getBasicBlock()) {
       if (BB->hasName()) {
         BB->printAsOperand(OutStreamer->GetCommentOS(),
                            /*PrintType=*/false, BB->getModule());
         OutStreamer->GetCommentOS() << '\n';
       }
     }
-    emitBasicBlockLoopComments(MBB, LI, *this);
+
+    // Get MachineDominatorTree or compute it on the fly if it's unavailable
+    auto *MDT = getAnalysisIfAvailable<MachineDominatorTree>();
+    MachineDominatorTree ComputedMDT;
+    if (!MDT) {
+      ComputedMDT.getBase().recalculate(*MF);
+      MDT = &ComputedMDT;
+    }
+
+    // Get MachineLoopInfo or compute it on the fly if it's unavailable
+    auto *MLI = getAnalysisIfAvailable<MachineLoopInfo>();
+    MachineLoopInfo ComputedMLI;
+    if (!MLI) {
+      ComputedMLI.getBase().analyze(MDT->getBase());
+      MLI = &ComputedMLI;
+    }
+
+    emitBasicBlockLoopComments(MBB, MLI, *this);
   }
 
   // Print the main label for the block.
   if (MBB.pred_empty() ||
       (isBlockOnlyReachableByFallthrough(&MBB) && !MBB.isEHFuncletEntry())) {
     if (isVerbose()) {
       // NOTE: Want this comment at start of line, don't emit with AddComment.
       OutStreamer->emitRawComment(" %bb." + Twine(MBB.getNumber()) + ":",

llvm/test/CodeGen/AArch64/O0-pipeline.ll

 ; CHECK-NEXT:       Contiguously Lay Out Funclets
 ; CHECK-NEXT:       StackMap Liveness Analysis
 ; CHECK-NEXT:       Live DEBUG_VALUE analysis
 ; CHECK-NEXT:       Insert fentry calls
 ; CHECK-NEXT:       Insert XRay ops
 ; CHECK-NEXT:       Implement the 'patchable-function' attribute
 ; CHECK-NEXT:       Lazy Machine Block Frequency Analysis
 ; CHECK-NEXT:       Machine Optimization Remark Emitter
-; CHECK-NEXT:       MachineDominator Tree Construction
-; CHECK-NEXT:       Machine Natural Loop Construction
 ; CHECK-NEXT:       AArch64 Assembly Printer
 ; CHECK-NEXT:       Free MachineFunction
 
 define void @f() {
   ret void
 }

llvm/test/CodeGen/AArch64/O3-pipeline.ll

 ; CHECK-NEXT:       Contiguously Lay Out Funclets
 ; CHECK-NEXT:       StackMap Liveness Analysis
 ; CHECK-NEXT:       Live DEBUG_VALUE analysis
 ; CHECK-NEXT:       Insert fentry calls
 ; CHECK-NEXT:       Insert XRay ops
 ; CHECK-NEXT:       Implement the 'patchable-function' attribute
 ; CHECK-NEXT:       Lazy Machine Block Frequency Analysis
 ; CHECK-NEXT:       Machine Optimization Remark Emitter
-; CHECK-NEXT:       MachineDominator Tree Construction
-; CHECK-NEXT:       Machine Natural Loop Construction
 ; CHECK-NEXT:       AArch64 Assembly Printer
 ; CHECK-NEXT:       Free MachineFunction
 ; CHECK-NEXT: Pass Arguments:  -domtree
 ; CHECK-NEXT:   FunctionPass Manager
 ; CHECK-NEXT:     Dominator Tree Construction
 
 define void @f() {
   ret void
 }

llvm/test/CodeGen/AArch64/arm64-opt-remarks-lazy-bfi.ll

 ; HOTNESS-NEXT: Executing Pass 'Lazy Machine Block Frequency Analysis'
 ; HOTNESS-NEXT: Executing Pass 'Machine Optimization Remark Emitter'
 ; HOTNESS-NEXT: Building MachineBlockFrequencyInfo on the fly
 ; HOTNESS-NEXT: Building LoopInfo on the fly
 ; HOTNESS-NEXT: Building DominatorTree on the fly
 ; HOTNESS-NOT: Executing Pass
 ; HOTNESS: block-frequency: empty_func
 ; HOTNESS-NOT: Executing Pass
-; HOTNESS: Executing Pass 'MachineDominator Tree Construction'
-; HOTNESS-NEXT: Executing Pass 'Machine Natural Loop Construction'
-; HOTNESS-NEXT: Executing Pass 'AArch64 Assembly Printer'
+; HOTNESS: Executing Pass 'AArch64 Assembly Printer'
 
 ; HOTNESS: arm64-summary-remarks.ll:5:0: 1 instructions in function (hotness: 33)
 
 
 ; NO_HOTNESS:      Executing Pass 'Implement the 'patchable-function' attribute'
 ; NO_HOTNESS-NEXT:  Freeing Pass 'Implement the 'patchable-function' attribute'
 ; NO_HOTNESS-NEXT: Executing Pass 'Lazy Machine Block Frequency Analysis'
 ; NO_HOTNESS-NEXT: Executing Pass 'Machine Optimization Remark Emitter'
-; NO_HOTNESS-NEXT: Executing Pass 'MachineDominator Tree Construction'
-; NO_HOTNESS-NEXT: Executing Pass 'Machine Natural Loop Construction'
 ; NO_HOTNESS-NEXT: Executing Pass 'AArch64 Assembly Printer'
 
 ; NO_HOTNESS: arm64-summary-remarks.ll:5:0: 1 instructions in function{{$}}
 
 define void @empty_func() nounwind ssp !dbg !3 !prof !4 {
   ret void
 }
 
 !llvm.dbg.cu = !{!0}
 !llvm.module.flags = !{!2}
 
 !0 = distinct !DICompileUnit(language: DW_LANG_C, file: !1)
 !1 = !DIFile(filename: "arm64-summary-remarks.ll", directory: "")
 !2 = !{i32 2, !"Debug Info Version", i32 3}
 !3 = distinct !DISubprogram(name: "empty_func", scope: !1, file: !1, line: 5, scopeLine: 5, unit: !0)
 !4 = !{!"function_entry_count", i64 33}

llvm/test/CodeGen/X86/O0-pipeline.ll

 ; CHECK-NEXT:       StackMap Liveness Analysis
 ; CHECK-NEXT:       Live DEBUG_VALUE analysis
 ; CHECK-NEXT:       Insert fentry calls
 ; CHECK-NEXT:       Insert XRay ops
 ; CHECK-NEXT:       Implement the 'patchable-function' attribute
 ; CHECK-NEXT:       X86 Retpoline Thunks
 ; CHECK-NEXT:       Lazy Machine Block Frequency Analysis
 ; CHECK-NEXT:       Machine Optimization Remark Emitter
-; CHECK-NEXT:       MachineDominator Tree Construction
-; CHECK-NEXT:       Machine Natural Loop Construction
 ; CHECK-NEXT:       X86 Assembly Printer
 ; CHECK-NEXT:       Free MachineFunction
 
 define void @f() {
   ret void
 }

llvm/test/CodeGen/X86/O3-pipeline.ll

 ; CHECK-NEXT:       StackMap Liveness Analysis
 ; CHECK-NEXT:       Live DEBUG_VALUE analysis
 ; CHECK-NEXT:       Insert fentry calls
 ; CHECK-NEXT:       Insert XRay ops
 ; CHECK-NEXT:       Implement the 'patchable-function' attribute
 ; CHECK-NEXT:       X86 Retpoline Thunks
 ; CHECK-NEXT:       Lazy Machine Block Frequency Analysis
 ; CHECK-NEXT:       Machine Optimization Remark Emitter
-; CHECK-NEXT:       MachineDominator Tree Construction
-; CHECK-NEXT:       Machine Natural Loop Construction
 ; CHECK-NEXT:       X86 Assembly Printer
 ; CHECK-NEXT:       Free MachineFunction
 
 define void @f() {
   ret void
 }