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Enable the new LoopInfo algorithm by default.

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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.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@159183 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Andrew Trick
2012-06-26 04:11:38 +00:00
parent 5ac3f96c0e
commit c9b1e25493
10 changed files with 52 additions and 244 deletions
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10
lib/CodeGen/MachineLoopInfo.cpp
View File

@ -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;
}