Do not remove implicit defs in BranchFolder

Branch folder removes implicit defs if they are the only non-branching
instructions in a block, and the branches do not use the defined registers.
The problem is that in some cases these implicit defs are required for
the liveness information to be correct.

Differential Revision: https://reviews.llvm.org/D25478

llvm-svn: 284036

1 files changed, 0 insertions, 54 deletions

diff --git a/llvm/lib/CodeGen/BranchFolding.cpp b/llvm/lib/CodeGen/BranchFolding.cpp
index ec736a04bbd..71074513c89 100644
--- a/llvm/lib/CodeGen/BranchFolding.cpp
+++ b/llvm/lib/CodeGen/BranchFolding.cpp
@@ -145,59 +145,6 @@ void BranchFolder::RemoveDeadBlock(MachineBasicBlock *MBB) {
     MLI->removeBlock(MBB);
 }
 
-/// OptimizeImpDefsBlock - If a basic block is just a bunch of implicit_def
-/// followed by terminators, and if the implicitly defined registers are not
-/// used by the terminators, remove those implicit_def's. e.g.
-/// BB1:
-///   r0 = implicit_def
-///   r1 = implicit_def
-///   br
-/// This block can be optimized away later if the implicit instructions are
-/// removed.
-bool BranchFolder::OptimizeImpDefsBlock(MachineBasicBlock *MBB) {
-  SmallSet<unsigned, 4> ImpDefRegs;
-  MachineBasicBlock::iterator I = MBB->begin();
-  while (I != MBB->end()) {
-    if (!I->isImplicitDef())
-      break;
-    unsigned Reg = I->getOperand(0).getReg();
-    if (TargetRegisterInfo::isPhysicalRegister(Reg)) {
-      for (MCSubRegIterator SubRegs(Reg, TRI, /*IncludeSelf=*/true);
-           SubRegs.isValid(); ++SubRegs)
-        ImpDefRegs.insert(*SubRegs);
-    } else {
-      ImpDefRegs.insert(Reg);
-    }
-    ++I;
-  }
-  if (ImpDefRegs.empty())
-    return false;
-
-  MachineBasicBlock::iterator FirstTerm = I;
-  while (I != MBB->end()) {
-    if (!TII->isUnpredicatedTerminator(*I))
-      return false;
-    // See if it uses any of the implicitly defined registers.
-    for (const MachineOperand &MO : I->operands()) {
-      if (!MO.isReg() || !MO.isUse())
-        continue;
-      unsigned Reg = MO.getReg();
-      if (ImpDefRegs.count(Reg))
-        return false;
-    }
-    ++I;
-  }
-
-  I = MBB->begin();
-  while (I != FirstTerm) {
-    MachineInstr *ImpDefMI = &*I;
-    ++I;
-    MBB->erase(ImpDefMI);
-  }
-
-  return true;
-}
-
 /// OptimizeFunction - Perhaps branch folding, tail merging and other
 /// CFG optimizations on the given function.  Block placement changes the layout
 /// and may create new tail merging opportunities.
@@ -228,7 +175,6 @@ bool BranchFolder::OptimizeFunction(MachineFunction &MF,
     SmallVector<MachineOperand, 4> Cond;
     if (!TII->analyzeBranch(MBB, TBB, FBB, Cond, true))
       MadeChange |= MBB.CorrectExtraCFGEdges(TBB, FBB, !Cond.empty());
-    MadeChange |= OptimizeImpDefsBlock(&MBB);
   }
 
   // Recalculate funclet membership.