Revert "[MachinePipeliner] Improve the TargetInstrInfo API analyzeLoop/reduceLoopCount"

This commit broke the ASan buildbot. See comments in rL372376 for more
information.

This reverts commit 15e27b0b6d9d51362fad85dbe95ac5b3fadf0a06.

llvm-svn: 372425

1 files changed, 23 insertions, 17 deletions

diff --git a/llvm/lib/CodeGen/ModuloSchedule.cpp b/llvm/lib/CodeGen/ModuloSchedule.cpp
index aa5e86e97d1..8bea4037f54 100644
--- a/llvm/lib/CodeGen/ModuloSchedule.cpp
+++ b/llvm/lib/CodeGen/ModuloSchedule.cpp
@@ -105,9 +105,6 @@ void ModuloScheduleExpander::expand() {
 }
 
 void ModuloScheduleExpander::generatePipelinedLoop() {
-  LoopInfo = TII->analyzeLoopForPipelining(BB);
-  assert(LoopInfo && "Must be able to analyze loop!");
-
   // Create a new basic block for the kernel and add it to the CFG.
   MachineBasicBlock *KernelBB = MF.CreateMachineBasicBlock(BB->getBasicBlock());
 
@@ -850,6 +847,10 @@ void ModuloScheduleExpander::addBranches(MachineBasicBlock &PreheaderBB,
                                          MBBVectorTy &EpilogBBs,
                                          ValueMapTy *VRMap) {
   assert(PrologBBs.size() == EpilogBBs.size() && "Prolog/Epilog mismatch");
+  MachineInstr *IndVar;
+  MachineInstr *Cmp;
+  if (TII->analyzeLoop(*Schedule.getLoop(), IndVar, Cmp))
+    llvm_unreachable("Must be able to analyze loop!");
   MachineBasicBlock *LastPro = KernelBB;
   MachineBasicBlock *LastEpi = KernelBB;
 
@@ -857,20 +858,32 @@ void ModuloScheduleExpander::addBranches(MachineBasicBlock &PreheaderBB,
   // to the first prolog and the last epilog blocks.
   SmallVector<MachineInstr *, 4> PrevInsts;
   unsigned MaxIter = PrologBBs.size() - 1;
+  unsigned LC = UINT_MAX;
+  unsigned LCMin = UINT_MAX;
   for (unsigned i = 0, j = MaxIter; i <= MaxIter; ++i, --j) {
     // Add branches to the prolog that go to the corresponding
     // epilog, and the fall-thru prolog/kernel block.
     MachineBasicBlock *Prolog = PrologBBs[j];
     MachineBasicBlock *Epilog = EpilogBBs[i];
-
+    // We've executed one iteration, so decrement the loop count and check for
+    // the loop end.
     SmallVector<MachineOperand, 4> Cond;
-    Optional<bool> StaticallyGreater =
-        LoopInfo->createTripCountGreaterCondition(j + 1, *Prolog, Cond);
+    // Check if the LOOP0 has already been removed. If so, then there is no need
+    // to reduce the trip count.
+    if (LC != 0)
+      LC = TII->reduceLoopCount(*Prolog, PreheaderBB, IndVar, *Cmp, Cond,
+                                PrevInsts, j, MaxIter);
+
+    // Record the value of the first trip count, which is used to determine if
+    // branches and blocks can be removed for constant trip counts.
+    if (LCMin == UINT_MAX)
+      LCMin = LC;
+
     unsigned numAdded = 0;
-    if (!StaticallyGreater.hasValue()) {
+    if (Register::isVirtualRegister(LC)) {
       Prolog->addSuccessor(Epilog);
       numAdded = TII->insertBranch(*Prolog, Epilog, LastPro, Cond, DebugLoc());
-    } else if (*StaticallyGreater == false) {
+    } else if (j >= LCMin) {
       Prolog->addSuccessor(Epilog);
       Prolog->removeSuccessor(LastPro);
       LastEpi->removeSuccessor(Epilog);
@@ -881,12 +894,10 @@ void ModuloScheduleExpander::addBranches(MachineBasicBlock &PreheaderBB,
         LastEpi->clear();
         LastEpi->eraseFromParent();
       }
-      if (LastPro == KernelBB) {
-        LoopInfo->disposed();
-        NewKernel = nullptr;
-      }
       LastPro->clear();
       LastPro->eraseFromParent();
+      if (LastPro == KernelBB)
+        NewKernel = nullptr;
     } else {
       numAdded = TII->insertBranch(*Prolog, LastPro, nullptr, Cond, DebugLoc());
       removePhis(Epilog, Prolog);
@@ -898,11 +909,6 @@ void ModuloScheduleExpander::addBranches(MachineBasicBlock &PreheaderBB,
          I != E && numAdded > 0; ++I, --numAdded)
       updateInstruction(&*I, false, j, 0, VRMap);
   }
-
-  if (NewKernel) {
-    LoopInfo->setPreheader(PrologBBs[MaxIter]);
-    LoopInfo->adjustTripCount(-(MaxIter + 1));
-  }
 }
 
 /// Return true if we can compute the amount the instruction changes