Clean come dead code

These codes deleted are dead code, we never go into it.
1. In AggressiveAntiDepBreaker.cpp, have assert AntiDepReg != 0.
2. IfConversion.cpp, Kind can only be one unique value, so isFalse && isRev
    can never be true.
3. DAGCombiner.cpp, at line 3675, we have considered the condition like
```
  // fold (sub x, c) -> (add x, -c)
  if (N1C) {
    return DAG.getNode(ISD::ADD, DL, VT, N0,
                       DAG.getConstant(-N1C->getAPIntValue(), DL, VT));
  }
```
4. ScheduleDAGSDNodes.cpp, we have Latency > 1 at line 663
5. MasmParser.cpp, code exists in a switch-case block which decided by
    the value FirstTokenKind, at line 1621, FirstTokenKind could only be
    one of AsmToken::Dollar, AsmToken::At and AsmToken::Identifier.

Reviewed By: skan

Differential Revision: https://reviews.llvm.org/D148610

Author: XinWang10

llvm/lib/CodeGen/AggressiveAntiDepBreaker.cpp

@@ -920,7 +920,6 @@ unsigned AggressiveAntiDepBreaker::BreakAntiDependencies(
         }
 
         assert(AntiDepReg != 0);
-        if (AntiDepReg == 0) continue;
 
         // Determine AntiDepReg's register group.
         const unsigned GroupIndex = State->GetGroup(AntiDepReg);

llvm/lib/CodeGen/IfConversion.cpp

@@ -71,8 +71,6 @@ static cl::opt<bool> DisableTriangleR("disable-ifcvt-triangle-rev",
                                       cl::init(false), cl::Hidden);
 static cl::opt<bool> DisableTriangleF("disable-ifcvt-triangle-false",
                                       cl::init(false), cl::Hidden);
-static cl::opt<bool> DisableTriangleFR("disable-ifcvt-triangle-false-rev",
-                                       cl::init(false), cl::Hidden);
 static cl::opt<bool> DisableDiamond("disable-ifcvt-diamond",
                                     cl::init(false), cl::Hidden);
 static cl::opt<bool> DisableForkedDiamond("disable-ifcvt-forked-diamond",
@@ -532,7 +530,6 @@ bool IfConverter::runOnMachineFunction(MachineFunction &MF) {
         if (DisableTriangle && !isFalse && !isRev) break;
         if (DisableTriangleR && !isFalse && isRev) break;
         if (DisableTriangleF && isFalse && !isRev) break;
-        if (DisableTriangleFR && isFalse && isRev) break;
         LLVM_DEBUG(dbgs() << "Ifcvt (Triangle");
         if (isFalse)
           LLVM_DEBUG(dbgs() << " false");

llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

@@ -3934,11 +3934,6 @@ SDValue DAGCombiner::visitSUB(SDNode *N) {
   // If the relocation model supports it, consider symbol offsets.
   if (GlobalAddressSDNode *GA = dyn_cast<GlobalAddressSDNode>(N0))
     if (!LegalOperations && TLI.isOffsetFoldingLegal(GA)) {
-      // fold (sub Sym, c) -> Sym-c
-      if (N1C && GA->getOpcode() == ISD::GlobalAddress)
-        return DAG.getGlobalAddress(GA->getGlobal(), SDLoc(N1C), VT,
-                                    GA->getOffset() -
-                                        (uint64_t)N1C->getSExtValue());
       // fold (sub Sym+c1, Sym+c2) -> c1-c2
       if (GlobalAddressSDNode *GB = dyn_cast<GlobalAddressSDNode>(N1))
         if (GA->getGlobal() == GB->getGlobal())

llvm/lib/CodeGen/SelectionDAG/ScheduleDAGSDNodes.cpp

@@ -667,7 +667,7 @@ void ScheduleDAGSDNodes::computeOperandLatency(SDNode *Def, SDNode *Use,
       // This copy is a liveout value. It is likely coalesced, so reduce the
       // latency so not to penalize the def.
       // FIXME: need target specific adjustment here?
-      Latency = (Latency > 1) ? Latency - 1 : 1;
+      Latency = Latency - 1;
   }
   if (Latency >= 0)
     dep.setLatency(Latency);

llvm/lib/MC/MCParser/MasmParser.cpp

@@ -1618,19 +1618,7 @@ bool MasmParser::parsePrimaryExpr(const MCExpr *&Res, SMLoc &EndLoc,
     // Parse symbol variant.
     std::pair<StringRef, StringRef> Split;
     if (!MAI.useParensForSymbolVariant()) {
-      if (FirstTokenKind == AsmToken::String) {
-        if (Lexer.is(AsmToken::At)) {
-          Lex(); // eat @
-          SMLoc AtLoc = getLexer().getLoc();
-          StringRef VName;
-          if (parseIdentifier(VName))
-            return Error(AtLoc, "expected symbol variant after '@'");
-
-          Split = std::make_pair(Identifier, VName);
-        }
-      } else {
-        Split = Identifier.split('@');
-      }
+      Split = Identifier.split('@');
     } else if (Lexer.is(AsmToken::LParen)) {
       Lex(); // eat '('.
       StringRef VName;