[llvm-commits] [llvm] r65120 - /llvm/trunk/lib/CodeGen/StackSlotColoring.cpp

[Evan Cheng]

It probably should only do DCE when any coloring was done, right?

Evan

On Feb 20, 2009, at 1:11 AM, Owen Anderson wrote:

> Author: resistor
> Date: Fri Feb 20 03:11:36 2009
> New Revision: 65120
>
> URL: http://llvm.org/viewvc/llvm-project?rev=65120&view=rev
> Log:
> Add a quick pass to the stack slot colorer to eliminate some  
> trivially redundant spills after coloring.
> Ideally these would never get created in the first place, but until  
> we enhance the spiller to have a more
> global picture of what's happening, this is necessary for code  
> quality in some circumstances.
>
> Modified:
>    llvm/trunk/lib/CodeGen/StackSlotColoring.cpp
>
> Modified: llvm/trunk/lib/CodeGen/StackSlotColoring.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/StackSlotColoring.cpp?rev=65120&r1=65119&r2=65120&view=diff
>
> = 
> = 
> = 
> = 
> = 
> = 
> = 
> = 
> ======================================================================
> --- llvm/trunk/lib/CodeGen/StackSlotColoring.cpp (original)
> +++ llvm/trunk/lib/CodeGen/StackSlotColoring.cpp Fri Feb 20 03:11:36  
> 2009
> @@ -19,6 +19,8 @@
> #include "llvm/Support/CommandLine.h"
> #include "llvm/Support/Compiler.h"
> #include "llvm/Support/Debug.h"
> +#include "llvm/Target/TargetInstrInfo.h"
> +#include "llvm/Target/TargetMachine.h"
> #include "llvm/ADT/BitVector.h"
> #include "llvm/ADT/SmallVector.h"
> #include "llvm/ADT/Statistic.h"
> @@ -30,12 +32,20 @@
>              cl::init(false), cl::Hidden,
>              cl::desc("Surpress slot sharing during stack coloring"));
>
> +static cl::opt<bool>
> +EnableDCE("enable-ssc-dce",
> +               cl::init(false), cl::Hidden,
> +               cl::desc("Enable slot coloring DCE"));
> +
> STATISTIC(NumEliminated,   "Number of stack slots eliminated due to  
> coloring");
> +STATISTIC(NumDeadAccesses,
> +                          "Number of trivially dead stack accesses  
> eliminated");
>
> namespace {
>   class VISIBILITY_HIDDEN StackSlotColoring : public  
> MachineFunctionPass {
>     LiveStacks* LS;
>     MachineFrameInfo *MFI;
> +    const TargetInstrInfo  *TII;
>
>     // SSIntervals - Spill slot intervals.
>     std::vector<LiveInterval*> SSIntervals;
> @@ -67,6 +77,7 @@
>
>     virtual void getAnalysisUsage(AnalysisUsage &AU) const {
>       AU.addRequired<LiveStacks>();
> +
>       AU.addPreservedID(MachineLoopInfoID);
>       AU.addPreservedID(MachineDominatorsID);
>       MachineFunctionPass::getAnalysisUsage(AU);
> @@ -82,6 +93,7 @@
>     bool OverlapWithAssignments(LiveInterval *li, int Color) const;
>     int ColorSlot(LiveInterval *li);
>     bool ColorSlots(MachineFunction &MF);
> +    bool removeDeadStores(MachineBasicBlock* MBB);
>   };
> } // end anonymous namespace
>
> @@ -260,10 +272,55 @@
>   return true;
> }
>
> +/// removeDeadStores - Scan through a basic block and look for  
> loads followed
> +/// by stores.  If they're both using the same stack slot, then the  
> store is
> +/// definitely dead.  This could obviously be much more aggressive  
> (consider
> +/// pairs with instructions between them), but such extensions  
> might have a
> +/// considerable compile time impact.
> +bool StackSlotColoring::removeDeadStores(MachineBasicBlock* MBB) {
> +  // FIXME: This could be much more aggressive, but we need to  
> investigate
> +  // the compile time impact of doing so.
> +  bool changed = false;
> +
> +  SmallVector<MachineInstr*, 4> toErase;
> +
> +  for (MachineBasicBlock::iterator I = MBB->begin(), E = MBB->end();
> +       I != E; ++I) {
> +    MachineBasicBlock::iterator NextMI = next(I);
> +    if (NextMI == MBB->end()) continue;
> +
> +    int FirstSS, SecondSS;
> +    unsigned LoadReg = 0;
> +    unsigned StoreReg = 0;
> +    if (!(LoadReg = TII->isLoadFromStackSlot(I, FirstSS))) continue;
> +    if (!(StoreReg = TII->isStoreToStackSlot(NextMI, SecondSS)))  
> continue;
> +    if (FirstSS != SecondSS || LoadReg != StoreReg || FirstSS ==  
> -1) continue;
> +
> +    ++NumDeadAccesses;
> +    changed = true;
> +
> +    if (NextMI->findRegisterUseOperandIdx(LoadReg, true, 0) != -1) {
> +      ++NumDeadAccesses;
> +      toErase.push_back(I);
> +    }
> +
> +    toErase.push_back(NextMI);
> +    ++I;
> +  }
> +
> +  for (SmallVector<MachineInstr*, 4>::iterator I = toErase.begin(),
> +       E = toErase.end(); I != E; ++I)
> +    (*I)->eraseFromParent();
> +
> +  return changed;
> +}
> +
> +
> bool StackSlotColoring::runOnMachineFunction(MachineFunction &MF) {
>   DOUT << "********** Stack Slot Coloring **********\n";
>
>   MFI = MF.getFrameInfo();
> +  TII = MF.getTarget().getInstrInfo();
>   LS = &getAnalysis<LiveStacks>();
>
>   bool Changed = false;
> @@ -280,5 +337,10 @@
>     Assignments[i].clear();
>   Assignments.clear();
>
> +  if (EnableDCE) {
> +    for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I ! 
> = E; ++I)
> +      Changed |= removeDeadStores(I);
> +  }
> +
>   return Changed;
> }
>
>
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