[X86, Peephole] Enable FoldImmediate for X86

Enable FoldImmediate for X86 by implementing X86InstrInfo::FoldImmediate.

Also enhanced peephole by deleting identical instructions after FoldImmediate.

Differential Revision: https://reviews.llvm.org/D151848

Author: weiguozhi

llvm/lib/CodeGen/PeepholeOptimizer.cpp

@@ -202,7 +202,8 @@ namespace {
     bool isMoveImmediate(MachineInstr &MI, SmallSet<Register, 4> &ImmDefRegs,
                          DenseMap<Register, MachineInstr *> &ImmDefMIs);
     bool foldImmediate(MachineInstr &MI, SmallSet<Register, 4> &ImmDefRegs,
-                       DenseMap<Register, MachineInstr *> &ImmDefMIs);
+                       DenseMap<Register, MachineInstr *> &ImmDefMIs,
+                       bool &Deleted);
 
     /// Finds recurrence cycles, but only ones that formulated around
     /// a def operand and a use operand that are tied. If there is a use
@@ -217,8 +218,11 @@ namespace {
     /// set \p CopyMIs. If this virtual register was previously seen as a
     /// copy, replace the uses of this copy with the previously seen copy's
     /// destination register.
+    /// \p LocalMIs contains all previous seen instructions. An optimized away
+    /// instruction should be deleted from LocalMIs.
     bool foldRedundantCopy(MachineInstr &MI,
-                           DenseMap<RegSubRegPair, MachineInstr *> &CopyMIs);
+                           DenseMap<RegSubRegPair, MachineInstr *> &CopyMIs,
+                           SmallPtrSetImpl<MachineInstr *> &LocalMIs);
 
     /// Is the register \p Reg a non-allocatable physical register?
     bool isNAPhysCopy(Register Reg);
@@ -1351,26 +1355,28 @@ bool PeepholeOptimizer::isMoveImmediate(
     MachineInstr &MI, SmallSet<Register, 4> &ImmDefRegs,
     DenseMap<Register, MachineInstr *> &ImmDefMIs) {
   const MCInstrDesc &MCID = MI.getDesc();
-  if (!MI.isMoveImmediate())
-    return false;
-  if (MCID.getNumDefs() != 1)
+  if (MCID.getNumDefs() != 1 || !MI.getOperand(0).isReg())
     return false;
   Register Reg = MI.getOperand(0).getReg();
-  if (Reg.isVirtual()) {
-    ImmDefMIs.insert(std::make_pair(Reg, &MI));
-    ImmDefRegs.insert(Reg);
-    return true;
-  }
+  if (!Reg.isVirtual())
+    return false;
 
-  return false;
+  int64_t ImmVal;
+  if (!MI.isMoveImmediate() && !TII->getConstValDefinedInReg(MI, Reg, ImmVal))
+    return false;
+
+  ImmDefMIs.insert(std::make_pair(Reg, &MI));
+  ImmDefRegs.insert(Reg);
+  return true;
 }
 
 /// 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, SmallSet<Register, 4> &ImmDefRegs,
-    DenseMap<Register, MachineInstr *> &ImmDefMIs) {
+    DenseMap<Register, MachineInstr *> &ImmDefMIs, bool &Deleted) {
+  Deleted = false;
   for (unsigned i = 0, e = MI.getDesc().getNumOperands(); i != e; ++i) {
     MachineOperand &MO = MI.getOperand(i);
     if (!MO.isReg() || MO.isDef())
@@ -1384,6 +1390,19 @@ bool PeepholeOptimizer::foldImmediate(
     assert(II != ImmDefMIs.end() && "couldn't find immediate definition");
     if (TII->FoldImmediate(MI, *II->second, Reg, MRI)) {
       ++NumImmFold;
+      // FoldImmediate can delete ImmDefMI if MI was its only user. If ImmDefMI
+      // is not deleted, and we happened to get a same MI, we can delete MI and
+      // replace its users.
+      if (MRI->getVRegDef(Reg) &&
+          MI.isIdenticalTo(*II->second, MachineInstr::IgnoreVRegDefs)) {
+        Register DstReg = MI.getOperand(0).getReg();
+        if (DstReg.isVirtual() &&
+            MRI->getRegClass(DstReg) == MRI->getRegClass(Reg)) {
+          MRI->replaceRegWith(DstReg, Reg);
+          MI.eraseFromParent();
+          Deleted = true;
+        }
+      }
       return true;
     }
   }
@@ -1405,7 +1424,8 @@ bool PeepholeOptimizer::foldImmediate(
 //
 // Should replace %2 uses with %1:sub1
 bool PeepholeOptimizer::foldRedundantCopy(
-    MachineInstr &MI, DenseMap<RegSubRegPair, MachineInstr *> &CopyMIs) {
+    MachineInstr &MI, DenseMap<RegSubRegPair, MachineInstr *> &CopyMIs,
+    SmallPtrSetImpl<MachineInstr *> &LocalMIs) {
   assert(MI.isCopy() && "expected a COPY machine instruction");
 
   Register SrcReg = MI.getOperand(1).getReg();
@@ -1425,6 +1445,8 @@ bool PeepholeOptimizer::foldRedundantCopy(
   }
 
   MachineInstr *PrevCopy = CopyMIs.find(SrcPair)->second;
+  if (!LocalMIs.count(PrevCopy))
+    return false;
 
   assert(SrcSubReg == PrevCopy->getOperand(1).getSubReg() &&
          "Unexpected mismatching subreg!");
@@ -1732,7 +1754,7 @@ bool PeepholeOptimizer::runOnMachineFunction(MachineFunction &MF) {
         continue;
       }
 
-      if (MI->isCopy() && (foldRedundantCopy(*MI, CopySrcMIs) ||
+      if (MI->isCopy() && (foldRedundantCopy(*MI, CopySrcMIs, LocalMIs) ||
                            foldRedundantNAPhysCopy(*MI, NAPhysToVirtMIs))) {
         LocalMIs.erase(MI);
         LLVM_DEBUG(dbgs() << "Deleting redundant copy: " << *MI << "\n");
@@ -1750,8 +1772,14 @@ bool PeepholeOptimizer::runOnMachineFunction(MachineFunction &MF) {
         // next iteration sees the new instructions.
         MII = MI;
         ++MII;
-        if (SeenMoveImm)
-          Changed |= foldImmediate(*MI, ImmDefRegs, ImmDefMIs);
+        if (SeenMoveImm) {
+          bool Deleted;
+          Changed |= foldImmediate(*MI, ImmDefRegs, ImmDefMIs, Deleted);
+          if (Deleted) {
+            LocalMIs.erase(MI);
+            continue;
+          }
+        }
       }
 
       // Check whether MI is a load candidate for folding into a later