Enable the new LoopInfo algorithm by default.

The primary advantage is that loop optimizations will be applied in a
stable order. This helps debugging and unit test creation. It is also
a better overall implementation without pathologically bad performance
on deep functions.

On large functions (llvm-stress --size=200000 | opt -loops)
Before: 0.1263s
After:  0.0225s

On deep functions (after tweaking llvm-stress, thanks Nadav):
Before: 0.2281s
After:  0.0227s

See r158790 for more comments.

The loop tree is now consistently generated in forward order, but loop
passes are applied in reverse order over the program. If we have a
loop optimization that prefers forward order, that can easily be
achieved by adding a different type of LoopPassManager.

llvm-svn: 159183

1 files changed, 1 insertions, 9 deletions

diff --git a/llvm/lib/CodeGen/MachineLoopInfo.cpp b/llvm/lib/CodeGen/MachineLoopInfo.cpp
index b7298e48eef..9f3829e3c0f 100644
--- a/llvm/lib/CodeGen/MachineLoopInfo.cpp
+++ b/llvm/lib/CodeGen/MachineLoopInfo.cpp
@@ -18,7 +18,6 @@
 #include "llvm/CodeGen/MachineDominators.h"
 #include "llvm/CodeGen/Passes.h"
 #include "llvm/Analysis/LoopInfoImpl.h"
-#include "llvm/Support/CommandLine.h"
 #include "llvm/Support/Debug.h"
 using namespace llvm;
 
@@ -26,10 +25,6 @@ using namespace llvm;
 template class llvm::LoopBase<MachineBasicBlock, MachineLoop>;
 template class llvm::LoopInfoBase<MachineBasicBlock, MachineLoop>;
 
-static cl::opt<bool>
-StableLoopInfo("stable-machine-loops", cl::Hidden, cl::init(false),
-               cl::desc("Compute a stable loop tree."));
-
 char MachineLoopInfo::ID = 0;
 INITIALIZE_PASS_BEGIN(MachineLoopInfo, "machine-loops",
                 "Machine Natural Loop Construction", true, true)
@@ -41,10 +36,7 @@ char &llvm::MachineLoopInfoID = MachineLoopInfo::ID;
 
 bool MachineLoopInfo::runOnMachineFunction(MachineFunction &) {
   releaseMemory();
-  if (StableLoopInfo)
-    LI.Analyze(getAnalysis<MachineDominatorTree>().getBase());
-  else
-    LI.Calculate(getAnalysis<MachineDominatorTree>().getBase());    // Update
+  LI.Analyze(getAnalysis<MachineDominatorTree>().getBase());
   return false;
 }