Revert "[MBP] Reduce code size by running tail merging in MBP."

This reverts commit r271930, r271915, r271923.  They break a thumb selfhosting
bot.

llvm-svn: 272017

llvm/lib/CodeGen/BranchFolding.cpp

@@ -27,7 +27,6 @@
 #include "llvm/CodeGen/MachineFunctionPass.h"
 #include "llvm/CodeGen/MachineJumpTableInfo.h"
 #include "llvm/CodeGen/MachineMemOperand.h"
-#include "llvm/CodeGen/MachineLoopInfo.h"
 #include "llvm/CodeGen/MachineModuleInfo.h"
 #include "llvm/CodeGen/MachineRegisterInfo.h"
 #include "llvm/CodeGen/Passes.h"
@@ -100,9 +99,8 @@ bool BranchFolderPass::runOnMachineFunction(MachineFunction &MF) {
   // HW that requires structurized CFG.
   bool EnableTailMerge = !MF.getTarget().requiresStructuredCFG() &&
                          PassConfig->getEnableTailMerge();
-  BranchFolder::MBFIWrapper MBBFreqInfo(
+  BranchFolder Folder(EnableTailMerge, /*CommonHoist=*/true,
-      getAnalysis<MachineBlockFrequencyInfo>());
+                      getAnalysis<MachineBlockFrequencyInfo>(),
-  BranchFolder Folder(EnableTailMerge, /*CommonHoist=*/true, MBBFreqInfo,
                       getAnalysis<MachineBranchProbabilityInfo>());
   return Folder.OptimizeFunction(MF, MF.getSubtarget().getInstrInfo(),
                                  MF.getSubtarget().getRegisterInfo(),
@@ -110,7 +108,7 @@ bool BranchFolderPass::runOnMachineFunction(MachineFunction &MF) {
 }
 
 BranchFolder::BranchFolder(bool defaultEnableTailMerge, bool CommonHoist,
-                           MBFIWrapper &FreqInfo,
+                           const MachineBlockFrequencyInfo &FreqInfo,
                            const MachineBranchProbabilityInfo &ProbInfo)
     : EnableHoistCommonCode(CommonHoist), MBBFreqInfo(FreqInfo),
       MBPI(ProbInfo) {
@@ -138,8 +136,6 @@ void BranchFolder::RemoveDeadBlock(MachineBasicBlock *MBB) {
   // Remove the block.
   MF->erase(MBB);
   FuncletMembership.erase(MBB);
-  if (MLI)
-    MLI->removeBlock(MBB);
 }
 
 /// OptimizeImpDefsBlock - If a basic block is just a bunch of implicit_def
@@ -196,22 +192,18 @@ bool BranchFolder::OptimizeImpDefsBlock(MachineBasicBlock *MBB) {
 }
 
 /// OptimizeFunction - Perhaps branch folding, tail merging and other
-/// CFG optimizations on the given function.  Block placement changes the layout
+/// CFG optimizations on the given function.
-/// and may create new tail merging opportunities.
 bool BranchFolder::OptimizeFunction(MachineFunction &MF,
                                     const TargetInstrInfo *tii,
                                     const TargetRegisterInfo *tri,
-                                    MachineModuleInfo *mmi,
+                                    MachineModuleInfo *mmi) {
-                                    MachineLoopInfo *mli, bool AfterPlacement) {
   if (!tii) return false;
 
   TriedMerging.clear();
 
-  AfterBlockPlacement = AfterPlacement;
   TII = tii;
   TRI = tri;
   MMI = mmi;
-  MLI = mli;
   RS = nullptr;
 
   // Use a RegScavenger to help update liveness when required.
@@ -237,10 +229,7 @@ bool BranchFolder::OptimizeFunction(MachineFunction &MF,
   bool MadeChangeThisIteration = true;
   while (MadeChangeThisIteration) {
     MadeChangeThisIteration    = TailMergeBlocks(MF);
-    // No need to clean up if tail merging does not change anything after the
+    MadeChangeThisIteration   |= OptimizeBranches(MF);
-    // block placement.
-    if (!AfterBlockPlacement || MadeChangeThisIteration)
-      MadeChangeThisIteration |= OptimizeBranches(MF);
     if (EnableHoistCommonCode)
       MadeChangeThisIteration |= HoistCommonCode(MF);
     MadeChange |= MadeChangeThisIteration;
@@ -457,11 +446,6 @@ MachineBasicBlock *BranchFolder::SplitMBBAt(MachineBasicBlock &CurMBB,
   // Splice the code over.
   NewMBB->splice(NewMBB->end(), &CurMBB, BBI1, CurMBB.end());
 
-  // NewMBB belongs to the same loop as CurMBB.
-  if (MLI) 
-    if (MachineLoop *ML = MLI->getLoopFor(&CurMBB))
-      ML->addBasicBlockToLoop(NewMBB, MLI->getBase());
-
   // NewMBB inherits CurMBB's block frequency.
   MBBFreqInfo.setBlockFreq(NewMBB, MBBFreqInfo.getBlockFreq(&CurMBB));
 
@@ -556,18 +540,6 @@ void BranchFolder::MBFIWrapper::setBlockFreq(const MachineBasicBlock *MBB,
   MergedBBFreq[MBB] = F;
 }
 
-raw_ostream &
-BranchFolder::MBFIWrapper::printBlockFreq(raw_ostream &OS,
-                                          const MachineBasicBlock *MBB) const {
-  return MBFI.printBlockFreq(OS, getBlockFreq(MBB));
-}
-
-raw_ostream &
-BranchFolder::MBFIWrapper::printBlockFreq(raw_ostream &OS,
-                                          const BlockFrequency Freq) const {
-  return MBFI.printBlockFreq(OS, Freq);
-}
-
 /// CountTerminators - Count the number of terminators in the given
 /// block and set I to the position of the first non-terminator, if there
 /// is one, or MBB->end() otherwise.
@@ -949,28 +921,24 @@ bool BranchFolder::TailMergeBlocks(MachineFunction &MF) {
   if (!EnableTailMerge) return MadeChange;
 
   // First find blocks with no successors.
-  // Block placement does not create new tail merging opportunities for these
+  MergePotentials.clear();
-  // blocks.
+  for (MachineBasicBlock &MBB : MF) {
-  if (!AfterBlockPlacement) {
-    MergePotentials.clear();
-    for (MachineBasicBlock &MBB : MF) {
-      if (MergePotentials.size() == TailMergeThreshold)
-        break;
-      if (!TriedMerging.count(&MBB) && MBB.succ_empty())
-        MergePotentials.push_back(MergePotentialsElt(HashEndOfMBB(MBB), &MBB));
-    }
-
-    // If this is a large problem, avoid visiting the same basic blocks
-    // multiple times.
     if (MergePotentials.size() == TailMergeThreshold)
-      for (unsigned i = 0, e = MergePotentials.size(); i != e; ++i)
+      break;
-        TriedMerging.insert(MergePotentials[i].getBlock());
+    if (!TriedMerging.count(&MBB) && MBB.succ_empty())
-
+      MergePotentials.push_back(MergePotentialsElt(HashEndOfMBB(MBB), &MBB));
-    // See if we can do any tail merging on those.
-    if (MergePotentials.size() >= 2)
-      MadeChange |= TryTailMergeBlocks(nullptr, nullptr);
   }
 
+  // If this is a large problem, avoid visiting the same basic blocks
+  // multiple times.
+  if (MergePotentials.size() == TailMergeThreshold)
+    for (unsigned i = 0, e = MergePotentials.size(); i != e; ++i)
+      TriedMerging.insert(MergePotentials[i].getBlock());
+
+  // See if we can do any tail merging on those.
+  if (MergePotentials.size() >= 2)
+    MadeChange |= TryTailMergeBlocks(nullptr, nullptr);
+
   // Look at blocks (IBB) with multiple predecessors (PBB).
   // We change each predecessor to a canonical form, by
   // (1) temporarily removing any unconditional branch from the predecessor
@@ -1016,17 +984,6 @@ bool BranchFolder::TailMergeBlocks(MachineFunction &MF) {
       if (PBB->hasEHPadSuccessor())
         continue;
 
-      // Bail out if the loop header (IBB) is not the top of the loop chain
-      // after the block placement.  Otherwise, the common tail of IBB's
-      // predecessors may become the loop top if block placement is called again
-      // and the predecessors may branch to this common tail.
-      // FIXME: Relaxed this check if the algorithm of finding loop top is
-      // changed in MBP.
-      if (AfterBlockPlacement && MLI)
-        if (MachineLoop *ML = MLI->getLoopFor(IBB))
-          if (IBB == ML->getHeader() && ML == MLI->getLoopFor(PBB))
-            continue;
-
       MachineBasicBlock *TBB = nullptr, *FBB = nullptr;
       SmallVector<MachineOperand, 4> Cond;
       if (!TII->AnalyzeBranch(*PBB, TBB, FBB, Cond, true)) {

llvm/lib/CodeGen/BranchFolding.h

@@ -20,24 +20,20 @@ namespace llvm {
   class MachineBranchProbabilityInfo;
   class MachineFunction;
   class MachineModuleInfo;
-  class MachineLoopInfo;
   class RegScavenger;
   class TargetInstrInfo;
   class TargetRegisterInfo;
 
   class LLVM_LIBRARY_VISIBILITY BranchFolder {
   public:
-    class MBFIWrapper;
-
     explicit BranchFolder(bool defaultEnableTailMerge, bool CommonHoist,
-                          MBFIWrapper &MBFI,
+                          const MachineBlockFrequencyInfo &MBFI,
                           const MachineBranchProbabilityInfo &MBPI);
 
-    bool OptimizeFunction(MachineFunction &MF, const TargetInstrInfo *tii,
+    bool OptimizeFunction(MachineFunction &MF,
-                          const TargetRegisterInfo *tri, MachineModuleInfo *mmi,
+                          const TargetInstrInfo *tii,
-                          MachineLoopInfo *mli = nullptr,
+                          const TargetRegisterInfo *tri,
-                          bool AfterPlacement = false);
+                          MachineModuleInfo *mmi);
-
   private:
     class MergePotentialsElt {
       unsigned Hash;
@@ -95,16 +91,13 @@ namespace llvm {
     };
     std::vector<SameTailElt> SameTails;
 
-    bool AfterBlockPlacement;
     bool EnableTailMerge;
     bool EnableHoistCommonCode;
     const TargetInstrInfo *TII;
     const TargetRegisterInfo *TRI;
     MachineModuleInfo *MMI;
-    MachineLoopInfo *MLI;
     RegScavenger *RS;
 
-  public:
     /// \brief This class keeps track of branch frequencies of newly created
     /// blocks and tail-merged blocks.
     class MBFIWrapper {
@@ -112,18 +105,13 @@ namespace llvm {
       MBFIWrapper(const MachineBlockFrequencyInfo &I) : MBFI(I) {}
       BlockFrequency getBlockFreq(const MachineBasicBlock *MBB) const;
       void setBlockFreq(const MachineBasicBlock *MBB, BlockFrequency F);
-      raw_ostream &printBlockFreq(raw_ostream &OS,
-                                  const MachineBasicBlock *MBB) const;
-      raw_ostream &printBlockFreq(raw_ostream &OS,
-                                  const BlockFrequency Freq) const;
 
     private:
       const MachineBlockFrequencyInfo &MBFI;
       DenseMap<const MachineBasicBlock *, BlockFrequency> MergedBBFreq;
     };
 
-  private:
+    MBFIWrapper MBBFreqInfo;
-    MBFIWrapper &MBBFreqInfo;
     const MachineBranchProbabilityInfo &MBPI;
 
     bool TailMergeBlocks(MachineFunction &MF);

llvm/lib/CodeGen/IfConversion.cpp

@@ -163,6 +163,7 @@ namespace {
     const TargetLoweringBase *TLI;
     const TargetInstrInfo *TII;
     const TargetRegisterInfo *TRI;
+    const MachineBlockFrequencyInfo *MBFI;
     const MachineBranchProbabilityInfo *MBPI;
     MachineRegisterInfo *MRI;
 
@@ -290,7 +291,7 @@ bool IfConverter::runOnMachineFunction(MachineFunction &MF) {
   TLI = ST.getTargetLowering();
   TII = ST.getInstrInfo();
   TRI = ST.getRegisterInfo();
-  BranchFolder::MBFIWrapper MBFI(getAnalysis<MachineBlockFrequencyInfo>());
+  MBFI = &getAnalysis<MachineBlockFrequencyInfo>();
   MBPI = &getAnalysis<MachineBranchProbabilityInfo>();
   MRI = &MF.getRegInfo();
   SchedModel.init(ST.getSchedModel(), &ST, TII);
@@ -302,7 +303,7 @@ bool IfConverter::runOnMachineFunction(MachineFunction &MF) {
   bool BFChange = false;
   if (!PreRegAlloc) {
     // Tail merge tend to expose more if-conversion opportunities.
-    BranchFolder BF(true, false, MBFI, *MBPI);
+    BranchFolder BF(true, false, *MBFI, *MBPI);
     BFChange = BF.OptimizeFunction(MF, TII, ST.getRegisterInfo(),
                                    getAnalysisIfAvailable<MachineModuleInfo>());
   }
@@ -426,7 +427,7 @@ bool IfConverter::runOnMachineFunction(MachineFunction &MF) {
   BBAnalysis.clear();
 
   if (MadeChange && IfCvtBranchFold) {
-    BranchFolder BF(false, false, MBFI, *MBPI);
+    BranchFolder BF(false, false, *MBFI, *MBPI);
     BF.OptimizeFunction(MF, TII, MF.getSubtarget().getRegisterInfo(),
                         getAnalysisIfAvailable<MachineModuleInfo>());
   }

llvm/lib/CodeGen/MachineBlockPlacement.cpp

@@ -26,8 +26,6 @@
 //===----------------------------------------------------------------------===//
 
 #include "llvm/CodeGen/Passes.h"
-#include "llvm/CodeGen/TargetPassConfig.h"
-#include "BranchFolding.h"
 #include "llvm/ADT/DenseMap.h"
 #include "llvm/ADT/SmallPtrSet.h"
 #include "llvm/ADT/SmallVector.h"
@@ -118,12 +116,6 @@ static cl::opt<unsigned> JumpInstCost("jump-inst-cost",
                                       cl::desc("Cost of jump instructions."),
                                       cl::init(1), cl::Hidden);
 
-static cl::opt<bool>
-BranchFoldPlacement("branch-fold-placement",
-              cl::desc("Perform branch folding during placement. "
-                       "Reduces code size."),
-              cl::init(true), cl::Hidden);
-
 extern cl::opt<unsigned> StaticLikelyProb;
 
 namespace {
@@ -240,10 +232,10 @@ class MachineBlockPlacement : public MachineFunctionPass {
   const MachineBranchProbabilityInfo *MBPI;
 
   /// \brief A handle to the function-wide block frequency pass.
-  std::unique_ptr<BranchFolder::MBFIWrapper> MBFI;
+  const MachineBlockFrequencyInfo *MBFI;
 
   /// \brief A handle to the loop info.
-  MachineLoopInfo *MLI;
+  const MachineLoopInfo *MLI;
 
   /// \brief A handle to the target's instruction info.
   const TargetInstrInfo *TII;
@@ -331,7 +323,6 @@ public:
     AU.addRequired<MachineBlockFrequencyInfo>();
     AU.addRequired<MachineDominatorTree>();
     AU.addRequired<MachineLoopInfo>();
-    AU.addRequired<TargetPassConfig>();
     MachineFunctionPass::getAnalysisUsage(AU);
   }
 };
@@ -1471,8 +1462,7 @@ bool MachineBlockPlacement::runOnMachineFunction(MachineFunction &F) {
     return false;
 
   MBPI = &getAnalysis<MachineBranchProbabilityInfo>();
-  MBFI = llvm::make_unique<BranchFolder::MBFIWrapper>(
+  MBFI = &getAnalysis<MachineBlockFrequencyInfo>();
-      getAnalysis<MachineBlockFrequencyInfo>());
   MLI = &getAnalysis<MachineLoopInfo>();
   TII = F.getSubtarget().getInstrInfo();
   TLI = F.getSubtarget().getTargetLowering();
@@ -1480,29 +1470,6 @@ bool MachineBlockPlacement::runOnMachineFunction(MachineFunction &F) {
   assert(BlockToChain.empty());
 
   buildCFGChains(F);
-
-  // Changing the layout can create new tail merging opportunities.
-  TargetPassConfig *PassConfig = &getAnalysis<TargetPassConfig>();
-  // TailMerge can create jump into if branches that make CFG irreducible for
-  // HW that requires structurized CFG.
-  bool EnableTailMerge = !F.getTarget().requiresStructuredCFG() &&
-                         PassConfig->getEnableTailMerge() &&
-                         BranchFoldPlacement;
-  // No tail merging opportunities if the block number is less than four.
-  if (F.size() > 3 && EnableTailMerge) {
-    BranchFolder BF(/*EnableTailMerge=*/true, /*CommonHoist=*/false, *MBFI,
-                    *MBPI);
-
-    if (BF.OptimizeFunction(F, TII, F.getSubtarget().getRegisterInfo(),
-                            getAnalysisIfAvailable<MachineModuleInfo>(), MLI,
-                            /*AfterBlockPlacement=*/true)) {
-      // Redo the layout if tail merging creates/removes/moves blocks.
-      BlockToChain.clear();
-      ChainAllocator.DestroyAll();
-      buildCFGChains(F);
-    }
-  }
-
   optimizeBranches(F);
   alignBlocks(F);
 

llvm/test/CodeGen/AArch64/tailmerging_in_mbp.ll

@@ -1,63 +0,0 @@
-; RUN: llc <%s -march=aarch64 | FileCheck %s
-
-; CHECK-LABEL: test:
-; CHECK:       LBB0_7:
-; CHECK:         b.hi	
-; CHECK-NEXT:    b	
-; CHECK-NEXT:  LBB0_8:
-; CHECK-NEXT:    mov	 x8, x9
-; CHECK-NEXT:  LBB0_9:
-define i64 @test(i64 %n, i64* %a, i64* %b, i64* %c, i64* %d, i64* %e, i64* %f) {
-entry:
-  %cmp28 = icmp sgt i64 %n, 1
-  br i1 %cmp28, label %for.body, label %for.end
-
-for.body:                                         ; preds = %for.body.lr.ph, %if.end
-  %j = phi i64 [ %n, %entry ], [ %div, %if.end ]
-  %div = lshr i64 %j, 1
-  %a.arrayidx = getelementptr inbounds i64, i64* %a, i64 %div
-  %a.j = load i64, i64* %a.arrayidx
-  %b.arrayidx = getelementptr inbounds i64, i64* %b, i64 %div
-  %b.j = load i64, i64* %b.arrayidx
-  %cmp.i = icmp slt i64 %a.j, %b.j
-  br i1 %cmp.i, label %for.end.loopexit, label %cond.false.i
-
-cond.false.i:                                     ; preds = %for.body
-  %cmp4.i = icmp sgt i64 %a.j, %b.j
-  br i1 %cmp4.i, label %if.end, label %cond.false6.i
-
-cond.false6.i:                                    ; preds = %cond.false.i
-  %c.arrayidx = getelementptr inbounds i64, i64* %c, i64 %div
-  %c.j = load i64, i64* %c.arrayidx
-  %d.arrayidx = getelementptr inbounds i64, i64* %d, i64 %div
-  %d.j = load i64, i64* %d.arrayidx
-  %cmp9.i = icmp slt i64 %c.j, %d.j
-  br i1 %cmp9.i, label %for.end.loopexit, label %cond.false11.i
-
-cond.false11.i:                                   ; preds = %cond.false6.i
-  %cmp14.i = icmp sgt i64 %c.j, %d.j
-  br i1 %cmp14.i, label %if.end, label %cond.false12.i
-
-cond.false12.i:                           ; preds = %cond.false11.i
-  %e.arrayidx = getelementptr inbounds i64, i64* %e, i64 %div
-  %e.j = load i64, i64* %e.arrayidx
-  %f.arrayidx = getelementptr inbounds i64, i64* %f, i64 %div
-  %f.j = load i64, i64* %f.arrayidx
-  %cmp19.i = icmp sgt i64 %e.j, %f.j
-  br i1 %cmp19.i, label %if.end, label %for.end.loopexit
-
-if.end:                                           ; preds = %cond.false12.i, %cond.false11.i, %cond.false.i
-  %cmp = icmp ugt i64 %j, 3
-  br i1 %cmp, label %for.body, label %for.end.loopexit
-
-for.end.loopexit:                                 ; preds = %cond.false12.i, %cond.false6.i, %for.body, %if.end
-  %j.0.lcssa.ph = phi i64 [ %j, %cond.false12.i ], [ %j, %cond.false6.i ], [ %j, %for.body ], [ %div, %if.end ]
-  br label %for.end
-
-for.end:                                          ; preds = %for.end.loopexit, %entry
-  %j.0.lcssa = phi i64 [ %n, %entry ], [ %j.0.lcssa.ph, %for.end.loopexit ]
-  %j.2 = add i64 %j.0.lcssa, %n
-  %j.3 = mul i64 %j.2, %n
-  %j.4 = add i64 %j.3, 10
-  ret i64 %j.4 
-}

llvm/test/CodeGen/ARM/arm-and-tst-peephole.ll

@@ -49,7 +49,7 @@ tailrecurse.switch:                               ; preds = %tailrecurse
 ; V8-NEXT: beq
 ; V8-NEXT: %tailrecurse.switch
 ; V8: cmp
-; V8-NEXT: beq
+; V8-NEXT: bne
 ; V8-NEXT: b	
 ; The trailing space in the last line checks that the branch is unconditional
   switch i32 %and, label %sw.epilog [