Add -reorder-basic-blocks option and fix nop insertion

src/IceCfgNode.cpp

 //===- subzero/src/IceCfgNode.cpp - Basic block (node) implementation -----===//
 //
 //                        The Subzero Code Generator
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 ///
 /// \file
@@ skipping 472 matching lines @@
   Context.init(this);
   while (!Context.atEnd()) {
     Target->doAddressOpt();
   }
 }
 
 void CfgNode::doNopInsertion() {
   TargetLowering *Target = Func->getTarget();
   LoweringContext &Context = Target->getContext();
   Context.init(this);
+  Context.setInsertPoint(Context.getCur());
+  // Do not insert nop in bundle locked instructions.
+  bool PauseNopInsertion = false;
   while (!Context.atEnd()) {
-    Target->doNopInsertion();
+    if (llvm::isa<InstBundleLock>(Context.getCur())) {
+      PauseNopInsertion = true;
+    } else if (llvm::isa<InstBundleUnlock>(Context.getCur())) {
+      PauseNopInsertion = false;
+    }
+    if (!PauseNopInsertion)
+      Target->doNopInsertion();

[jvoung (off chromium), 2015/07/29 18:09:18]

On BundleUnlock what happens? Does it insert nops before the BundleUnlock?

[qining, 2015/07/29 23:04:40]

On BundleUnlock, we resume nop insertion. At that time, Next should be pointing
to the next instruction just after bundle_unlock, and Cur should be
bundle_unlock instruction. So nop instructions will be inserted between
bundle_unlock and the next instruction after bundle_unlock, hence there should
not be any nop inserted before BundleUnlock.

     // Ensure Cur=Next, so that the nops are inserted before the current
     // instruction rather than after.
+    Context.advanceCur();
     Context.advanceNext();
-    Context.advanceCur();
   }
-  // Insert before all instructions.
-  Context.setInsertPoint(getInsts().begin());
-  Context.advanceNext();
-  Context.advanceCur();
-  Target->doNopInsertion();
 }
 
 // Drives the target lowering.  Passes the current instruction and the
 // next non-deleted instruction for target lowering.
 void CfgNode::genCode() {
   TargetLowering *Target = Func->getTarget();
   LoweringContext &Context = Target->getContext();
   // Lower the regular instructions.
   Context.init(this);
   Target->initNodeForLowering(this);
@@ skipping 751 matching lines @@
   InstIntrinsicCall *Inst = InstIntrinsicCall::create(
       Func, 5, Func->makeVariable(IceType_i64), RMWI64Name, Info->Info);
   Inst->addArg(AtomicRMWOp);
   Inst->addArg(Counter);
   Inst->addArg(One);
   Inst->addArg(OrderAcquireRelease);
   Insts.push_front(Inst);
 }
 
 } // end of namespace Ice