[Hexagon] Use constant extenders to fix up hardware loops

Use a loop instruction with a constant extender for a hardware
loop instruction that is too far away from the start of the loop.
This is cheaper than changing the SA register value.

Differential Revision: http://reviews.llvm.org/D9262


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@235882 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Target/Hexagon/HexagonFixupHwLoops.cpp

@@ -7,8 +7,7 @@
 //
 // The loop start address in the LOOPn instruction is encoded as a distance
 // from the LOOPn instruction itself. If the start address is too far from
-// the LOOPn instruction, the loop needs to be set up manually, i.e. via
-// direct transfers to SAn and LCn.
+// the LOOPn instruction, the instruction needs to use a constant extender.
 // This pass will identify and convert such LOOPn instructions to a proper
 // form.
 //===----------------------------------------------------------------------===//
@@ -21,12 +20,15 @@
 #include "llvm/CodeGen/MachineFunctionPass.h"
 #include "llvm/CodeGen/MachineInstrBuilder.h"
 #include "llvm/CodeGen/Passes.h"
-#include "llvm/CodeGen/RegisterScavenging.h"
 #include "llvm/PassSupport.h"
 #include "llvm/Target/TargetInstrInfo.h"
 
 using namespace llvm;
 
+static cl::opt<unsigned> MaxLoopRange(
+    "hexagon-loop-range", cl::Hidden, cl::init(200),
+    cl::desc("Restrict range of loopN instructions (testing only)"));
+
 namespace llvm {
   void initializeHexagonFixupHwLoopsPass(PassRegistry&);
 }
@@ -52,20 +54,15 @@ namespace {
     }
 
   private:
-    /// \brief Maximum distance between the loop instr and the basic block.
-    /// Just an estimate.
-    static const unsigned MAX_LOOP_DISTANCE = 200;
-
     /// \brief Check the offset between each loop instruction and
     /// the loop basic block to determine if we can use the LOOP instruction
     /// or if we need to set the LC/SA registers explicitly.
     bool fixupLoopInstrs(MachineFunction &MF);
 
-    /// \brief Add the instruction to set the LC and SA registers explicitly.
-    void convertLoopInstr(MachineFunction &MF,
-                          MachineBasicBlock::iterator &MII,
-                          RegScavenger &RS);
-
+    /// \brief Replace loop instruction with the constant extended
+    /// version if the loop label is too far from the loop instruction.
+    void useExtLoopInstr(MachineFunction &MF,
+                         MachineBasicBlock::iterator &MII);
   };
 
   char HexagonFixupHwLoops::ID = 0;
@@ -78,20 +75,18 @@ FunctionPass *llvm::createHexagonFixupHwLoops() {
   return new HexagonFixupHwLoops();
 }
 
-
 /// \brief Returns true if the instruction is a hardware loop instruction.
 static bool isHardwareLoop(const MachineInstr *MI) {
   return MI->getOpcode() == Hexagon::J2_loop0r ||
-         MI->getOpcode() == Hexagon::J2_loop0i;
+         MI->getOpcode() == Hexagon::J2_loop0i ||
+         MI->getOpcode() == Hexagon::J2_loop1r ||
+         MI->getOpcode() == Hexagon::J2_loop1i;
 }
 
-
 bool HexagonFixupHwLoops::runOnMachineFunction(MachineFunction &MF) {
-  bool Changed = fixupLoopInstrs(MF);
-  return Changed;
+  return fixupLoopInstrs(MF);
 }
 
-
 /// \brief For Hexagon, if the loop label is to far from the
 /// loop instruction then we need to set the LC0 and SA0 registers
 /// explicitly instead of using LOOP(start,count).  This function
@@ -105,41 +100,49 @@ bool HexagonFixupHwLoops::fixupLoopInstrs(MachineFunction &MF) {
   // Offset of the current instruction from the start.
   unsigned InstOffset = 0;
   // Map for each basic block to it's first instruction.
-  DenseMap<MachineBasicBlock*, unsigned> BlockToInstOffset;
+  DenseMap<const MachineBasicBlock *, unsigned> BlockToInstOffset;
+
+  const HexagonInstrInfo *HII =
+      static_cast<const HexagonInstrInfo *>(MF.getSubtarget().getInstrInfo());
 
   // First pass - compute the offset of each basic block.
-  for (MachineFunction::iterator MBB = MF.begin(), MBBe = MF.end();
-       MBB != MBBe; ++MBB) {
-    BlockToInstOffset[MBB] = InstOffset;
-    InstOffset += (MBB->size() * 4);
+  for (const MachineBasicBlock &MBB : MF) {
+    if (MBB.getAlignment()) {
+      // Although we don't know the exact layout of the final code, we need
+      // to account for alignment padding somehow. This heuristic pads each
+      // aligned basic block according to the alignment value.
+      int ByteAlign = (1u << MBB.getAlignment()) - 1;
+      InstOffset = (InstOffset + ByteAlign) & ~(ByteAlign);
     }
 
-  // Second pass - check each loop instruction to see if it needs to
-  // be converted.
+    BlockToInstOffset[&MBB] = InstOffset;
+    for (const MachineInstr &MI : MBB)
+      InstOffset += HII->getSize(&MI);
+  }
+
+  // Second pass - check each loop instruction to see if it needs to be
+  // converted.
   InstOffset = 0;
   bool Changed = false;
-  RegScavenger RS;
-
-  // Loop over all the basic blocks.
-  for (MachineFunction::iterator MBB = MF.begin(), MBBe = MF.end();
-       MBB != MBBe; ++MBB) {
-    InstOffset = BlockToInstOffset[MBB];
-    RS.enterBasicBlock(MBB);
+  for (MachineBasicBlock &MBB : MF) {
+    InstOffset = BlockToInstOffset[&MBB];
 
     // Loop over all the instructions.
-    MachineBasicBlock::iterator MIE = MBB->end();
-    MachineBasicBlock::iterator MII = MBB->begin();
+    MachineBasicBlock::iterator MII = MBB.begin();
+    MachineBasicBlock::iterator MIE = MBB.end();
     while (MII != MIE) {
+      InstOffset += HII->getSize(&*MII);
+      if (MII->isDebugValue()) {
+        ++MII;
+        continue;
+      }
       if (isHardwareLoop(MII)) {
-        RS.forward(MII);
         assert(MII->getOperand(0).isMBB() &&
                "Expect a basic block as loop operand");
-        int Sub = InstOffset - BlockToInstOffset[MII->getOperand(0).getMBB()];
-        unsigned Dist = Sub > 0 ? Sub : -Sub;
-        if (Dist > MAX_LOOP_DISTANCE) {
-          // Convert to explicity setting LC0 and SA0.
-          convertLoopInstr(MF, MII, RS);
-          MII = MBB->erase(MII);
+        int diff = InstOffset - BlockToInstOffset[MII->getOperand(0).getMBB()];
+        if ((unsigned)abs(diff) > MaxLoopRange) {
+          useExtLoopInstr(MF, MII);
+          MII = MBB.erase(MII);
           Changed = true;
         } else {
           ++MII;
@@ -147,39 +150,38 @@ bool HexagonFixupHwLoops::fixupLoopInstrs(MachineFunction &MF) {
       } else {
         ++MII;
       }
-      InstOffset += 4;
     }
   }
 
   return Changed;
 }
 
-
-/// \brief convert a loop instruction to a sequence of instructions that
-/// set the LC0 and SA0 register explicitly.
-void HexagonFixupHwLoops::convertLoopInstr(MachineFunction &MF,
-                                           MachineBasicBlock::iterator &MII,
-                                           RegScavenger &RS) {
+/// \brief Replace loop instructions with the constant extended version.
+void HexagonFixupHwLoops::useExtLoopInstr(MachineFunction &MF,
+                                          MachineBasicBlock::iterator &MII) {
   const TargetInstrInfo *TII = MF.getSubtarget().getInstrInfo();
   MachineBasicBlock *MBB = MII->getParent();
   DebugLoc DL = MII->getDebugLoc();
-  unsigned Scratch = RS.scavengeRegister(&Hexagon::IntRegsRegClass, MII, 0);
+  MachineInstrBuilder MIB;
+  unsigned newOp;
+  switch (MII->getOpcode()) {
+  case Hexagon::J2_loop0r:
+    newOp = Hexagon::J2_loop0rext;
+    break;
+  case Hexagon::J2_loop0i:
+    newOp = Hexagon::J2_loop0iext;
+    break;
+  case Hexagon::J2_loop1r:
+    newOp = Hexagon::J2_loop1rext;
+    break;
+  case Hexagon::J2_loop1i:
+    newOp = Hexagon::J2_loop1iext;
+    break;
+  default:
+    llvm_unreachable("Invalid Hardware Loop Instruction.");
+  }
+  MIB = BuildMI(*MBB, MII, DL, TII->get(newOp));
 
-  // First, set the LC0 with the trip count.
-  if (MII->getOperand(1).isReg()) {
-    // Trip count is a register
-    BuildMI(*MBB, MII, DL, TII->get(Hexagon::A2_tfrrcr), Hexagon::LC0)
-      .addReg(MII->getOperand(1).getReg());
-  } else {
-    // Trip count is an immediate.
-    BuildMI(*MBB, MII, DL, TII->get(Hexagon::A2_tfrsi), Scratch)
-      .addImm(MII->getOperand(1).getImm());
-    BuildMI(*MBB, MII, DL, TII->get(Hexagon::A2_tfrrcr), Hexagon::LC0)
-      .addReg(Scratch);
-  }
-  // Then, set the SA0 with the loop start address.
-  BuildMI(*MBB, MII, DL, TII->get(Hexagon::A2_tfrsi), Scratch)
-    .addMBB(MII->getOperand(0).getMBB());
-  BuildMI(*MBB, MII, DL, TII->get(Hexagon::A2_tfrrcr), Hexagon::SA0)
-    .addReg(Scratch);
+  for (unsigned i = 0; i < MII->getNumOperands(); ++i)
+    MIB.addOperand(MII->getOperand(i));
 }

lib/Target/Hexagon/HexagonInstrInfo.cpp

@@ -1742,14 +1742,14 @@ bool HexagonInstrInfo::isSchedulingBoundary(const MachineInstr *MI,
   return false;
 }
 
-bool HexagonInstrInfo::isConstExtended(MachineInstr *MI) const {
+bool HexagonInstrInfo::isConstExtended(const MachineInstr *MI) const {
   const uint64_t F = MI->getDesc().TSFlags;
   unsigned isExtended = (F >> HexagonII::ExtendedPos) & HexagonII::ExtendedMask;
   if (isExtended) // Instruction must be extended.
     return true;
 
-  unsigned isExtendable = (F >> HexagonII::ExtendablePos)
-                          & HexagonII::ExtendableMask;
+  unsigned isExtendable =
+    (F >> HexagonII::ExtendablePos) & HexagonII::ExtendableMask;
   if (!isExtendable)
     return false;
 
@@ -1785,6 +1785,27 @@ bool HexagonInstrInfo::isConstExtended(MachineInstr *MI) const {
   return (ImmValue < MinValue || ImmValue > MaxValue);
 }
 
+// Return the number of bytes required to encode the instruction.
+// Hexagon instructions are fixed length, 4 bytes, unless they
+// use a constant extender, which requires another 4 bytes.
+// For debug instructions and prolog labels, return 0.
+unsigned HexagonInstrInfo::getSize(const MachineInstr *MI) const {
+
+  if (MI->isDebugValue() || MI->isPosition())
+    return 0;
+
+  unsigned Size = MI->getDesc().getSize();
+  if (!Size)
+    // Assume the default insn size in case it cannot be determined
+    // for whatever reason.
+    Size = HEXAGON_INSTR_SIZE;
+
+  if (isConstExtended(MI) || isExtended(MI))
+    Size += HEXAGON_INSTR_SIZE;
+
+  return Size;
+}
+
 // Returns the opcode to use when converting MI, which is a conditional jump,
 // into a conditional instruction which uses the .new value of the predicate.
 // We also use branch probabilities to add a hint to the jump.

lib/Target/Hexagon/HexagonInstrInfo.h

@@ -1,3 +1,4 @@
+
 //===- HexagonInstrInfo.h - Hexagon Instruction Information -----*- C++ -*-===//
 //
 //                     The LLVM Compiler Infrastructure
@@ -203,7 +204,8 @@ public:
 
 
   void immediateExtend(MachineInstr *MI) const;
-  bool isConstExtended(MachineInstr *MI) const;
+  bool isConstExtended(const MachineInstr *MI) const;
+  unsigned getSize(const MachineInstr *MI) const;  
   int getDotNewPredJumpOp(MachineInstr *MI,
                       const MachineBranchProbabilityInfo *MBPI) const;
   unsigned getAddrMode(const MachineInstr* MI) const;

lib/Target/Hexagon/HexagonOperands.td

@@ -483,7 +483,9 @@ let PrintMethod = "printJumpTable" in
 def jumptablebase : Operand<i32>;
 
 def brtarget : Operand<OtherVT>;
-def brtargetExt : Operand<OtherVT>;
+def brtargetExt : Operand<OtherVT> {
+  let PrintMethod = "printExtBrtarget";
+}
 def calltarget : Operand<i32>;
 
 def bblabel : Operand<i32>;

lib/Target/Hexagon/MCTargetDesc/HexagonInstPrinter.cpp

@@ -249,3 +249,17 @@ void HexagonInstPrinter::printSymbol(const MCInst *MI, unsigned OpNo,
   printOperand(MI, OpNo, O);
   O << ')';
 }
+
+void HexagonInstPrinter::printExtBrtarget(const MCInst *MI, unsigned OpNo,
+                                          raw_ostream &O) const {
+  const MCOperand &MO = MI->getOperand(OpNo);
+  const MCInstrDesc &MII = getMII().get(MI->getOpcode());
+
+  assert((isExtendable(MII.TSFlags) || isExtended(MII.TSFlags)) &&
+         "Expecting an extendable operand");
+
+  if (MO.isExpr() || isExtended(MII.TSFlags)) {
+    O << "##";
+  }
+  printOperand(MI, OpNo, O);
+}

lib/Target/Hexagon/MCTargetDesc/HexagonInstPrinter.h

@@ -56,6 +56,7 @@ namespace llvm {
     void printGlobalOperand(const MCInst *MI, unsigned OpNo, raw_ostream &O)
            const;
     void printJumpTable(const MCInst *MI, unsigned OpNo, raw_ostream &O) const;
+    void printExtBrtarget(const MCInst *MI, unsigned OpNo, raw_ostream &O) const;
 
     void printConstantPool(const MCInst *MI, unsigned OpNo,
                            raw_ostream &O) const;

test/CodeGen/Hexagon/hwloop-range.ll

@@ -0,0 +1,36 @@
+; RUN: llc -march=hexagon -hexagon-loop-range=0 < %s | FileCheck %s
+
+; Test that the loop start address operand uses a constant extender
+; if the offset is out of range.
+
+; CHECK: loop0(##.LBB
+; CHECK: endloop0
+
+@g = external global i32, align 4
+
+define void @test(i32* nocapture %a, i32* nocapture readonly %b, i32 %n) #0 {
+entry:
+  %cmp6 = icmp slt i32 %n, 1
+  br i1 %cmp6, label %for.end, label %for.body.preheader
+
+for.body.preheader:
+  br label %for.body
+
+for.body:
+  %i.07 = phi i32 [ %inc, %for.body ], [ 0, %for.body.preheader ]
+  %arrayidx = getelementptr inbounds i32, i32* %b, i32 %i.07
+  %0 = load i32, i32* %arrayidx, align 4
+  %1 = load i32, i32* @g, align 4
+  %mul = mul nsw i32 %1, %0
+  %arrayidx1 = getelementptr inbounds i32, i32* %a, i32 %i.07
+  store i32 %mul, i32* %arrayidx1, align 4
+  %inc = add nuw nsw i32 %i.07, 1
+  %exitcond = icmp eq i32 %inc, %n
+  br i1 %exitcond, label %for.end.loopexit, label %for.body
+
+for.end.loopexit:
+  br label %for.end
+
+for.end:
+  ret void
+}