3 files changed, 87 insertions, 2 deletions

diff --git a/llvm/lib/Target/PowerPC/PPCInstrInfo.cpp b/llvm/lib/Target/PowerPC/PPCInstrInfo.cpp
index 99a52902a52..f25b929c808 100644
--- a/llvm/lib/Target/PowerPC/PPCInstrInfo.cpp
+++ b/llvm/lib/Target/PowerPC/PPCInstrInfo.cpp
@@ -2266,6 +2266,20 @@ static bool isZeroExtendingOp(const MachineInstr &MI) {
   return false;
 }
 
+// This function returns true if the input MachineInstr is a TOC save
+// instruction.
+bool PPCInstrInfo::isTOCSaveMI(const MachineInstr &MI) const {
+  if (!MI.getOperand(1).isImm() || !MI.getOperand(2).isReg())
+    return false;
+  unsigned TOCSaveOffset = Subtarget.getFrameLowering()->getTOCSaveOffset();
+  unsigned StackOffset = MI.getOperand(1).getImm();
+  unsigned StackReg = MI.getOperand(2).getReg();
+  if (StackReg == PPC::X1 && StackOffset == TOCSaveOffset)
+    return true;
+
+  return false;
+}
+
 // We limit the max depth to track incoming values of PHIs or binary ops
 // (e.g. AND) to avoid exsessive cost.
 const unsigned MAX_DEPTH = 1;
diff --git a/llvm/lib/Target/PowerPC/PPCInstrInfo.h b/llvm/lib/Target/PowerPC/PPCInstrInfo.h
index f7a44b89233..097faf7873c 100644
--- a/llvm/lib/Target/PowerPC/PPCInstrInfo.h
+++ b/llvm/lib/Target/PowerPC/PPCInstrInfo.h
@@ -297,6 +297,8 @@ public:
   const TargetRegisterClass *updatedRC(const TargetRegisterClass *RC) const;
   static int getRecordFormOpcode(unsigned Opcode);
 
+  bool isTOCSaveMI(const MachineInstr &MI) const;
+
   bool isSignOrZeroExtended(const MachineInstr &MI, bool SignExt,
                             const unsigned PhiDepth) const;
 
diff --git a/llvm/lib/Target/PowerPC/PPCMIPeephole.cpp b/llvm/lib/Target/PowerPC/PPCMIPeephole.cpp
index 0a84fe3bd41..a8d98133afc 100644
--- a/llvm/lib/Target/PowerPC/PPCMIPeephole.cpp
+++ b/llvm/lib/Target/PowerPC/PPCMIPeephole.cpp
@@ -29,13 +29,15 @@
 #include "llvm/CodeGen/MachineInstrBuilder.h"
 #include "llvm/CodeGen/MachineRegisterInfo.h"
 #include "llvm/Support/Debug.h"
-#include "llvm/ADT/Statistic.h"
 #include "MCTargetDesc/PPCPredicates.h"
 
 using namespace llvm;
 
 #define DEBUG_TYPE "ppc-mi-peepholes"
 
+STATISTIC(RemoveTOCSave, "Number of TOC saves removed");
+STATISTIC(MultiTOCSaves,
+          "Number of functions with multiple TOC saves that must be kept");
 STATISTIC(NumEliminatedSExt, "Number of eliminated sign-extensions");
 STATISTIC(NumEliminatedZExt, "Number of eliminated zero-extensions");
 STATISTIC(NumOptADDLIs, "Number of optimized ADD instruction fed by LI");
@@ -78,7 +80,9 @@ private:
 
   // Perform peepholes.
   bool eliminateRedundantCompare(void);
-
+  bool eliminateRedundantTOCSaves(std::map<MachineInstr *, bool> &TOCSaves);
+  void UpdateTOCSaves(std::map<MachineInstr *, bool> &TOCSaves,
+                      MachineInstr *MI);
   // Find the "true" register represented by SrcReg (following chains
   // of copies and subreg_to_reg operations).
   unsigned lookThruCopyLike(unsigned SrcReg);
@@ -176,10 +180,37 @@ getKnownLeadingZeroCount(MachineInstr *MI, const PPCInstrInfo *TII) {
   return 0;
 }
 
+// This function maintains a map for the pairs <TOC Save Instr, Keep>
+// Each time a new TOC save is encountered, it checks if any of the exisiting
+// ones are dominated by the new one. If so, it marks the exisiting one as
+// redundant by setting it's entry in the map as false. It then adds the new
+// instruction to the map with either true or false depending on if any
+// exisiting instructions dominated the new one.
+void PPCMIPeephole::UpdateTOCSaves(
+  std::map<MachineInstr *, bool> &TOCSaves, MachineInstr *MI) {
+  assert(TII->isTOCSaveMI(*MI) && "Expecting a TOC save instruction here");
+  bool Keep = true;
+  for (auto It = TOCSaves.begin(); It != TOCSaves.end(); It++ ) {
+    MachineInstr *CurrInst = It->first;
+    // If new instruction dominates an exisiting one, mark exisiting one as
+    // redundant.
+    if (It->second && MDT->dominates(MI, CurrInst))
+      It->second = false;
+    // Check if the new instruction is redundant.
+    if (MDT->dominates(CurrInst, MI)) {
+      Keep = false;
+      break;
+    }
+  }
+  // Add new instruction to map.
+  TOCSaves[MI] = Keep;
+}
+
 // Perform peephole optimizations.
 bool PPCMIPeephole::simplifyCode(void) {
   bool Simplified = false;
   MachineInstr* ToErase = nullptr;
+  std::map<MachineInstr *, bool> TOCSaves;
 
   for (MachineBasicBlock &MBB : *MF) {
     for (MachineInstr &MI : MBB) {
@@ -201,6 +232,18 @@ bool PPCMIPeephole::simplifyCode(void) {
       default:
         break;
 
+      case PPC::STD: {
+        MachineFrameInfo &MFI = MF->getFrameInfo();
+        if (MFI.hasVarSizedObjects() ||
+            !MF->getSubtarget<PPCSubtarget>().isELFv2ABI())
+          break;
+        // When encountering a TOC save instruction, call UpdateTOCSaves
+        // to add it to the TOCSaves map and mark any exisiting TOC saves
+        // it dominates as redundant.
+        if (TII->isTOCSaveMI(MI))
+          UpdateTOCSaves(TOCSaves, &MI);
+        break;
+      }
       case PPC::XXPERMDI: {
         // Perform simplifications of 2x64 vector swaps and splats.
         // A swap is identified by an immediate value of 2, and a splat
@@ -683,6 +726,8 @@ bool PPCMIPeephole::simplifyCode(void) {
     }
   }
 
+  // Eliminate all the TOC save instructions which are redundant.
+  Simplified |= eliminateRedundantTOCSaves(TOCSaves);
   // We try to eliminate redundant compare instruction.
   Simplified |= eliminateRedundantCompare();
 
@@ -888,6 +933,30 @@ static bool eligibleForCompareElimination(MachineBasicBlock &MBB,
   return false;
 }
 
+// This function will iterate over the input map containing a pair of TOC save
+// instruction and a flag. The flag will be set to false if the TOC save is proven
+// redundant. This function will erase from the basic block all the TOC saves
+// marked as redundant.
+bool PPCMIPeephole::eliminateRedundantTOCSaves(
+    std::map<MachineInstr *, bool> &TOCSaves) {
+  bool Simplified = false;
+  int NumKept = 0;
+  for (auto TOCSave : TOCSaves) {
+    if (!TOCSave.second) {
+      TOCSave.first->eraseFromParent();
+      RemoveTOCSave++;
+      Simplified = true;
+    } else {
+      NumKept++;
+    }
+  }
+
+  if (NumKept > 1)
+    MultiTOCSaves++;
+
+  return Simplified;
+}
+
 // If multiple conditional branches are executed based on the (essentially)
 // same comparison, we merge compare instructions into one and make multiple
 // conditional branches on this comparison.