[PowerPC] Remove redundant TOC saves

This patch adds a peep hole optimization to remove any redundant toc save
instructions added as part of the call sequence for indirect calls. It removes
any toc saves within a function that are dominated by another toc save.

Differential Revision: https://reviews.llvm.org/D39736

llvm-svn: 319087

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;

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;
 

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.

llvm/test/CodeGen/PowerPC/remove-redundant-toc-saves.ll

@@ -0,0 +1,123 @@
+; RUN: llc -verify-machineinstrs -mtriple=powerpc64le-unknown-linux-gnu < %s | FileCheck %s
+define signext i32 @test1(i32 signext %i, i32 (i32)* nocapture %Func, i32 (i32)* nocapture %Func2) {
+entry:
+; CHECK-LABEL: test1:
+; CHECK:    std 2, 24(1)
+; CHECK-NOT:    std 2, 24(1)
+  %call = tail call signext i32 %Func(i32 signext %i)
+  %call1 = tail call signext i32 %Func2(i32 signext %i)
+  %add2 = add nsw i32 %call1, %call
+  ret i32 %add2
+}
+
+define signext i32 @test2(i32 signext %i, i32 signext %j, i32 (i32)* nocapture %Func, i32 (i32)* nocapture %Func2) {
+entry:
+; CHECK-LABEL: test2:
+; CHECK:    std 2, 24(1)
+; CHECK-NOT:    std 2, 24(1)
+  %call = tail call signext i32 %Func(i32 signext %i)
+  %tobool = icmp eq i32 %j, 0
+  br i1 %tobool, label %if.end, label %if.then
+
+if.then:                                          ; preds = %entry
+  %call1 = tail call signext i32 %Func(i32 signext %i)
+  %add2 = add nsw i32 %call1, %call
+  %call3 = tail call signext i32 %Func2(i32 signext %i)
+  %add4 = add nsw i32 %add2, %call3
+  br label %if.end
+
+if.end:                                           ; preds = %entry, %if.then
+  %Sum.0 = phi i32 [ %add4, %if.then ], [ %call, %entry ]
+  %call5 = tail call signext i32 %Func(i32 signext %i)
+  %add6 = add nsw i32 %call5, %Sum.0
+  ret i32 %add6
+}
+
+; Check for multiple TOC saves with if then else where neither dominates the other.
+define signext i32 @test3(i32 signext %i, i32 (i32)* nocapture %Func, i32 (i32)* nocapture %Func2) {
+; CHECK-LABEL: test3:
+; CHECK:    std 2, 24(1)
+; CHECK:    std 2, 24(1)
+; CHECK-NOT:    std 2, 24(1)
+entry:
+  %tobool = icmp eq i32 %i, 0
+  br i1 %tobool, label %if.else, label %if.then
+
+if.then:                                          ; preds = %entry
+  %call = tail call signext i32 %Func(i32 signext %i)
+  br label %if.end
+
+if.else:                                          ; preds = %entry
+  %call1 = tail call signext i32 %Func2(i32 signext 0)
+  br label %if.end
+
+if.end:                                           ; preds = %if.else, %if.then
+  %Sum.0 = phi i32 [ %call, %if.then ], [ %call1, %if.else ]
+  %call3 = tail call signext i32 %Func(i32 signext %i)
+  %add4 = add nsw i32 %call3, %Sum.0
+  ret i32 %add4
+}
+
+define signext i32 @test4(i32 signext %i, i32 (i32)* nocapture %Func, i32 (i32)* nocapture %Func2) {
+; CHECK-LABEL: test4:
+; CHECK:    std 2, 24(1)
+; CHECK-NOT:    std 2, 24(1)
+
+entry:
+  %call = tail call signext i32 %Func(i32 signext %i)
+  %tobool = icmp eq i32 %i, 0
+  br i1 %tobool, label %if.else, label %if.then
+
+if.then:                                          ; preds = %entry
+  %call1 = tail call signext i32 %Func(i32 signext %i)
+  br label %if.end
+
+if.else:                                          ; preds = %entry
+  %call3 = tail call signext i32 %Func2(i32 signext 0)
+  br label %if.end
+
+if.end:                                           ; preds = %if.else, %if.then
+  %call1.pn = phi i32 [ %call1, %if.then ], [ %call3, %if.else ]
+  %Sum.0 = add nsw i32 %call1.pn, %call
+  ret i32 %Sum.0
+}
+
+; Check for multiple TOC saves with if then where neither is redundant.
+define signext i32 @test5(i32 signext %i, i32 (i32)* nocapture %Func, i32 (i32)* nocapture readnone %Func2) {
+entry:
+; CHECK-LABEL: test5:
+; CHECK:    std 2, 24(1)
+; CHECK:    std 2, 24(1)
+
+  %tobool = icmp eq i32 %i, 0
+  br i1 %tobool, label %if.end, label %if.then
+
+if.then:                                          ; preds = %entry
+  %call = tail call signext i32 %Func(i32 signext %i)
+  br label %if.end
+
+if.end:                                           ; preds = %entry, %if.then
+  %Sum.0 = phi i32 [ %call, %if.then ], [ 0, %entry ]
+  %call1 = tail call signext i32 %Func(i32 signext %i)
+  %add2 = add nsw i32 %call1, %Sum.0
+  ret i32 %add2
+}
+
+; Check for multiple TOC saves if there are dynamic allocations on the stack.
+define signext i32 @test6(i32 signext %i, i32 (i32)* nocapture %Func, i32 (i32)* nocapture %Func2) {
+entry:
+; CHECK-LABEL: test6:
+; CHECK:    std 2, 24(1)
+; CHECK:    std 2, 24(1)
+
+  %conv = sext i32 %i to i64
+  %0 = alloca i8, i64 %conv, align 16
+  %1 = bitcast i8* %0 to i32*
+  %call = tail call signext i32 %Func(i32 signext %i)
+  call void @useAlloca(i32* nonnull %1, i32 signext %call)
+  %call1 = call signext i32 %Func2(i32 signext %i)
+  %add2 = add nsw i32 %call1, %call
+  ret i32 %add2
+}
+
+declare void @useAlloca(i32*, i32 signext)