#include "llvm/Target/TargetAsmInfo.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Support/Compiler.h"
+#include "llvm/Support/MathExtras.h"
using namespace llvm;
static Statistic<> NumExpanded("ppc-branch-select",
namespace {
struct VISIBILITY_HIDDEN PPCBSel : public MachineFunctionPass {
- /// OffsetMap - Mapping between BB # and byte offset from start of function.
- std::vector<unsigned> OffsetMap;
+ /// BlockSizes - The sizes of the basic blocks in the function.
+ std::vector<unsigned> BlockSizes;
virtual bool runOnMachineFunction(MachineFunction &Fn);
virtual const char *getPassName() const {
- return "PowerPC Branch Selection";
+ return "PowerPC Branch Selector";
}
};
}
///
static unsigned getNumBytesForInstruction(MachineInstr *MI) {
switch (MI->getOpcode()) {
- case PPC::BCC:
- // while this will be 4 most of the time, if we emit 8 it is just a
- // minor pessimization that saves us from having to worry about
- // keeping the offsets up to date later when we emit long branch glue.
- return 8;
case PPC::IMPLICIT_DEF_GPRC: // no asm emitted
case PPC::IMPLICIT_DEF_G8RC: // no asm emitted
case PPC::IMPLICIT_DEF_F4: // no asm emitted
bool PPCBSel::runOnMachineFunction(MachineFunction &Fn) {
- // Running total of instructions encountered since beginning of function
- unsigned ByteCount = 0;
-
- OffsetMap.resize(Fn.getNumBlockIDs());
-
- // For each MBB, add its offset to the offset map, and count up its
- // instructions
+ // Give the blocks of the function a dense, in-order, numbering.
+ Fn.RenumberBlocks();
+ BlockSizes.resize(Fn.getNumBlockIDs());
+
+ // Measure each MBB and compute a size for the entire function.
+ unsigned FuncSize = 0;
for (MachineFunction::iterator MFI = Fn.begin(), E = Fn.end(); MFI != E;
++MFI) {
MachineBasicBlock *MBB = MFI;
- OffsetMap[MBB->getNumber()] = ByteCount;
-
+
+ unsigned BlockSize = 0;
for (MachineBasicBlock::iterator MBBI = MBB->begin(), EE = MBB->end();
MBBI != EE; ++MBBI)
- ByteCount += getNumBytesForInstruction(MBBI);
+ BlockSize += getNumBytesForInstruction(MBBI);
+
+ BlockSizes[MBB->getNumber()] = BlockSize;
+ FuncSize += BlockSize;
}
- // We're about to run over the MBB's again, so reset the ByteCount
- ByteCount = 0;
+ // If the entire function is smaller than the displacement of a branch field,
+ // we know we don't need to shrink any branches in this function. This is a
+ // common case.
+ if (FuncSize < (1 << 15)) {
+ BlockSizes.clear();
+ return false;
+ }
- // For each MBB, find the conditional branch pseudo instructions, and
- // calculate the difference between the target MBB and the current ICount
- // to decide whether or not to emit a short or long branch.
- //
- // short branch:
- // bCC .L_TARGET_MBB
+ // For each conditional branch, if the offset to its destination is larger
+ // than the offset field allows, transform it into a long branch sequence
+ // like this:
+ // short branch:
+ // bCC MBB
+ // long branch:
+ // b!CC $PC+8
+ // b MBB
//
- // long branch:
- // bInverseCC $PC+8
- // b .L_TARGET_MBB
- for (MachineFunction::iterator MFI = Fn.begin(), E = Fn.end(); MFI != E;
- ++MFI) {
- MachineBasicBlock *MBB = MFI;
-
- for (MachineBasicBlock::iterator MBBI = MBB->begin(), EE = MBB->end();
- MBBI != EE; ++MBBI) {
- // We may end up deleting the MachineInstr that MBBI points to, so
- // remember its opcode now so we can refer to it after calling erase()
- unsigned ByteSize = getNumBytesForInstruction(MBBI);
- if (MBBI->getOpcode() != PPC::BCC) {
- ByteCount += ByteSize;
- continue;
- }
-
- // condbranch operands:
- // 0. CR register
- // 1. PPC branch opcode
- // 2. Target MBB
- MachineBasicBlock *DestMBB = MBBI->getOperand(2).getMachineBasicBlock();
- PPC::Predicate Pred = (PPC::Predicate)MBBI->getOperand(0).getImm();
- unsigned CRReg = MBBI->getOperand(1).getReg();
- int Displacement = OffsetMap[DestMBB->getNumber()] - ByteCount;
+ bool MadeChange = true;
+ bool EverMadeChange = false;
+ while (MadeChange) {
+ // Iteratively expand branches until we reach a fixed point.
+ MadeChange = false;
+
+ for (MachineFunction::iterator MFI = Fn.begin(), E = Fn.end(); MFI != E;
+ ++MFI) {
+ MachineBasicBlock &MBB = *MFI;
+ unsigned MBBStartOffset = 0;
+ for (MachineBasicBlock::iterator I = MBB.begin(), E = MBB.end();
+ I != E; ++I) {
+ if (I->getOpcode() != PPC::BCC || I->getOperand(2).isImm()) {
+ MBBStartOffset += getNumBytesForInstruction(I);
+ continue;
+ }
+
+ // Determine the offset from the current branch to the destination
+ // block.
+ MachineBasicBlock *Dest = I->getOperand(2).getMachineBasicBlock();
+
+ int BranchSize;
+ if (Dest->getNumber() <= MBB.getNumber()) {
+ // If this is a backwards branch, the delta is the offset from the
+ // start of this block to this branch, plus the sizes of all blocks
+ // from this block to the dest.
+ BranchSize = MBBStartOffset;
+
+ for (unsigned i = Dest->getNumber(), e = MBB.getNumber(); i != e; ++i)
+ BranchSize += BlockSizes[i];
+ } else {
+ // Otherwise, add the size of the blocks between this block and the
+ // dest to the number of bytes left in this block.
+ BranchSize = -MBBStartOffset;
+
+ for (unsigned i = MBB.getNumber(), e = Dest->getNumber(); i != e; ++i)
+ BranchSize += BlockSizes[i];
+ }
- bool ShortBranchOk = Displacement >= -32768 && Displacement <= 32767;
-
- // Branch on opposite condition if a short branch isn't ok.
- if (!ShortBranchOk)
- Pred = PPC::InvertPredicate(Pred);
+ // If this branch is in range, ignore it.
+ if (isInt16(BranchSize)) {
+ MBBStartOffset += 4;
+ continue;
+ }
- unsigned Opcode;
- switch (Pred) {
- default: assert(0 && "Unknown cond branch predicate!");
- case PPC::PRED_LT: Opcode = PPC::BLT; break;
- case PPC::PRED_LE: Opcode = PPC::BLE; break;
- case PPC::PRED_EQ: Opcode = PPC::BEQ; break;
- case PPC::PRED_GE: Opcode = PPC::BGE; break;
- case PPC::PRED_GT: Opcode = PPC::BGT; break;
- case PPC::PRED_NE: Opcode = PPC::BNE; break;
- case PPC::PRED_UN: Opcode = PPC::BUN; break;
- case PPC::PRED_NU: Opcode = PPC::BNU; break;
- }
-
- MachineBasicBlock::iterator MBBJ;
- if (ShortBranchOk) {
- MBBJ = BuildMI(*MBB, MBBI, Opcode, 2).addReg(CRReg).addMBB(DestMBB);
- } else {
- // Long branch, skip next branch instruction (i.e. $PC+8).
+ // Otherwise, we have to expand it to a long branch.
+ // The BCC operands are:
+ // 0. PPC branch predicate
+ // 1. CR register
+ // 2. Target MBB
+ PPC::Predicate Pred = (PPC::Predicate)I->getOperand(0).getImm();
+ unsigned CRReg = I->getOperand(1).getReg();
+
+ MachineInstr *OldBranch = I;
+
+ // Jump over the uncond branch inst (i.e. $PC+8) on opposite condition.
+ BuildMI(MBB, I, PPC::BCC, 3)
+ .addImm(PPC::InvertPredicate(Pred)).addReg(CRReg).addImm(2);
+
+ // Uncond branch to the real destination.
+ I = BuildMI(MBB, I, PPC::B, 1).addMBB(Dest);
+
+ // Remove the old branch from the function.
+ OldBranch->eraseFromParent();
+
+ // Remember that this instruction is 8-bytes, increase the size of the
+ // block by 4, remember to iterate.
+ BlockSizes[MBB.getNumber()] += 4;
+ MBBStartOffset += 8;
++NumExpanded;
- BuildMI(*MBB, MBBI, Opcode, 2).addReg(CRReg).addImm(2);
- MBBJ = BuildMI(*MBB, MBBI, PPC::B, 1).addMBB(DestMBB);
+ MadeChange = true;
}
-
- // Erase the psuedo BCC instruction, and then back up the
- // iterator so that when the for loop increments it, we end up in
- // the correct place rather than iterating off the end.
- MBB->erase(MBBI);
- MBBI = MBBJ;
- ByteCount += ByteSize;
}
+ EverMadeChange |= MadeChange;
}
- OffsetMap.clear();
+ BlockSizes.clear();
return true;
}
// BCC represents an arbitrary conditional branch on a predicate.
// FIXME: should be able to write a pattern for PPCcondbranch, but can't use
// a two-value operand where a dag node expects two operands. :(
- def BCC : CBForm<16, 0, 0, (ops pred:$cond, target:$dst),
- "b${cond:cc} ${cond:reg}, $dst"
- /*[(PPCcondbranch CRRC:$crS, imm:$opc, bb:$dst)]*/>;
-
-// REMOVE BForm when these go away.
- def BLT : BForm<16, 0, 0, 12, 0, (ops CRRC:$crS, target:$block),
- "blt $crS, $block", BrB>;
- def BLE : BForm<16, 0, 0, 4, 1, (ops CRRC:$crS, target:$block),
- "ble $crS, $block", BrB>;
- def BEQ : BForm<16, 0, 0, 12, 2, (ops CRRC:$crS, target:$block),
- "beq $crS, $block", BrB>;
- def BGE : BForm<16, 0, 0, 4, 0, (ops CRRC:$crS, target:$block),
- "bge $crS, $block", BrB>;
- def BGT : BForm<16, 0, 0, 12, 1, (ops CRRC:$crS, target:$block),
- "bgt $crS, $block", BrB>;
- def BNE : BForm<16, 0, 0, 4, 2, (ops CRRC:$crS, target:$block),
- "bne $crS, $block", BrB>;
- def BUN : BForm<16, 0, 0, 12, 3, (ops CRRC:$crS, target:$block),
- "bun $crS, $block", BrB>;
- def BNU : BForm<16, 0, 0, 4, 3, (ops CRRC:$crS, target:$block),
- "bnu $crS, $block", BrB>;
+ def BCC : BForm<16, 0, 0, (ops pred:$cond, target:$dst),
+ "b${cond:cc} ${cond:reg}, $dst"
+ /*[(PPCcondbranch CRRC:$crS, imm:$opc, bb:$dst)]*/>;
}
let isCall = 1, noResults = 1, PPC970_Unit = 7,
projects / oota-llvm.git / commitdiff