Remove ARM isel hacks that fold large immediates into a pair of add, sub, and,

and xor. The 32-bit move immediates can be hoisted out of loops by machine
LICM but the isel hacks were preventing them.

Instead, let peephole optimization pass recognize registers that are defined by
immediates and the ARM target hook will fold the immediates in.

Other changes include 1) do not fold and / xor into cmp to isel TST / TEQ
instructions if there are multiple uses. This happens when the 'and' is live
out, machine sink would have sinked the computation and that ends up pessimizing
code. The peephole pass would recognize situations where the 'and' can be
toggled to define CPSR and eliminate the comparison anyway.

2) Move peephole pass to after machine LICM, sink, and CSE to avoid blocking
important optimizations.

rdar://8663787, rdar://8241368

llvm-svn: 119548

1 files changed, 62 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/PeepholeOptimizer.cpp b/llvm/lib/CodeGen/PeepholeOptimizer.cpp
index 75f453ad71d..07c2b80dcb0 100644
--- a/llvm/lib/CodeGen/PeepholeOptimizer.cpp
+++ b/llvm/lib/CodeGen/PeepholeOptimizer.cpp
@@ -41,7 +41,9 @@
 #include "llvm/Target/TargetInstrInfo.h"
 #include "llvm/Target/TargetRegisterInfo.h"
 #include "llvm/Support/CommandLine.h"
+#include "llvm/ADT/DenseMap.h"
 #include "llvm/ADT/SmallPtrSet.h"
+#include "llvm/ADT/SmallSet.h"
 #include "llvm/ADT/Statistic.h"
 using namespace llvm;
 
@@ -56,6 +58,7 @@ DisablePeephole("disable-peephole", cl::Hidden, cl::init(false),
 
 STATISTIC(NumReuse,      "Number of extension results reused");
 STATISTIC(NumEliminated, "Number of compares eliminated");
+STATISTIC(NumImmFold,    "Number of move immediate foled");
 
 namespace {
   class PeepholeOptimizer : public MachineFunctionPass {
@@ -85,6 +88,12 @@ namespace {
     bool OptimizeCmpInstr(MachineInstr *MI, MachineBasicBlock *MBB);
     bool OptimizeExtInstr(MachineInstr *MI, MachineBasicBlock *MBB,
                           SmallPtrSet<MachineInstr*, 8> &LocalMIs);
+    bool isMoveImmediate(MachineInstr *MI,
+                         SmallSet<unsigned, 4> &ImmDefRegs,
+                         DenseMap<unsigned, MachineInstr*> &ImmDefMIs);
+    bool FoldImmediate(MachineInstr *MI, MachineBasicBlock *MBB,
+                       SmallSet<unsigned, 4> &ImmDefRegs,
+                       DenseMap<unsigned, MachineInstr*> &ImmDefMIs);
   };
 }
 
@@ -257,6 +266,49 @@ bool PeepholeOptimizer::OptimizeCmpInstr(MachineInstr *MI,
   return false;
 }
 
+bool PeepholeOptimizer::isMoveImmediate(MachineInstr *MI,
+                                        SmallSet<unsigned, 4> &ImmDefRegs,
+                                 DenseMap<unsigned, MachineInstr*> &ImmDefMIs) {
+  const TargetInstrDesc &TID = MI->getDesc();
+  if (!TID.isMoveImmediate())
+    return false;
+  if (TID.getNumDefs() != 1)
+    return false;
+  unsigned Reg = MI->getOperand(0).getReg();
+  if (TargetRegisterInfo::isVirtualRegister(Reg)) {
+    ImmDefMIs.insert(std::make_pair(Reg, MI));
+    ImmDefRegs.insert(Reg);
+    return true;
+  }
+  
+  return false;
+}
+
+/// FoldImmediate - Try folding register operands that are defined by move
+/// immediate instructions, i.e. a trivial constant folding optimization, if
+/// and only if the def and use are in the same BB.
+bool PeepholeOptimizer::FoldImmediate(MachineInstr *MI, MachineBasicBlock *MBB,
+                                      SmallSet<unsigned, 4> &ImmDefRegs,
+                                 DenseMap<unsigned, MachineInstr*> &ImmDefMIs) {
+  for (unsigned i = 0, e = MI->getDesc().getNumOperands(); i != e; ++i) {
+    MachineOperand &MO = MI->getOperand(i);
+    if (!MO.isReg() || MO.isDef())
+      continue;
+    unsigned Reg = MO.getReg();
+    if (!Reg || TargetRegisterInfo::isPhysicalRegister(Reg))
+      continue;
+    if (ImmDefRegs.count(Reg) == 0)
+      continue;
+    DenseMap<unsigned, MachineInstr*>::iterator II = ImmDefMIs.find(Reg);
+    assert(II != ImmDefMIs.end());
+    if (TII->FoldImmediate(MI, II->second, Reg, MRI)) {
+      ++NumImmFold;
+      return true;
+    }
+  }
+  return false;
+}
+
 bool PeepholeOptimizer::runOnMachineFunction(MachineFunction &MF) {
   if (DisablePeephole)
     return false;
@@ -269,9 +321,15 @@ bool PeepholeOptimizer::runOnMachineFunction(MachineFunction &MF) {
   bool Changed = false;
 
   SmallPtrSet<MachineInstr*, 8> LocalMIs;
+  SmallSet<unsigned, 4> ImmDefRegs;
+  DenseMap<unsigned, MachineInstr*> ImmDefMIs;
   for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I) {
     MachineBasicBlock *MBB = &*I;
+    
+    bool SeenMoveImm = false;
     LocalMIs.clear();
+    ImmDefRegs.clear();
+    ImmDefMIs.clear();
 
     for (MachineBasicBlock::iterator
            MII = I->begin(), MIE = I->end(); MII != MIE; ) {
@@ -283,8 +341,12 @@ bool PeepholeOptimizer::runOnMachineFunction(MachineFunction &MF) {
 
       if (MI->getDesc().isCompare()) {
         Changed |= OptimizeCmpInstr(MI, MBB);
+      } else if (isMoveImmediate(MI, ImmDefRegs, ImmDefMIs)) {
+        SeenMoveImm = true;
       } else {
         Changed |= OptimizeExtInstr(MI, MBB, LocalMIs);
+        if (SeenMoveImm)
+          Changed |= FoldImmediate(MI, MBB, ImmDefRegs, ImmDefMIs);
       }
     }
   }