From f1080f2bbebdb83121554274ae1c5d122bfd0b72 Mon Sep 17 00:00:00 2001 From: Anton Korobeynikov Date: Fri, 15 Jan 2010 21:19:05 +0000 Subject: [PATCH] Add branch relaxation pass (shamelessly stolen from PPC). llvm-svn: 93554 --- lib/Target/MSP430/MSP430.h | 2 + lib/Target/MSP430/MSP430BranchSelector.cpp | 179 +++++++++++++++++++++ lib/Target/MSP430/MSP430InstrInfo.cpp | 42 +++++ lib/Target/MSP430/MSP430InstrInfo.h | 18 +++ lib/Target/MSP430/MSP430InstrInfo.td | 9 +- lib/Target/MSP430/MSP430TargetMachine.cpp | 6 + lib/Target/MSP430/MSP430TargetMachine.h | 1 + 7 files changed, 256 insertions(+), 1 deletion(-) create mode 100644 lib/Target/MSP430/MSP430BranchSelector.cpp diff --git a/lib/Target/MSP430/MSP430.h b/lib/Target/MSP430/MSP430.h index 1ff178d99d9..e74211807c0 100644 --- a/lib/Target/MSP430/MSP430.h +++ b/lib/Target/MSP430/MSP430.h @@ -39,6 +39,8 @@ namespace llvm { FunctionPass *createMSP430ISelDag(MSP430TargetMachine &TM, CodeGenOpt::Level OptLevel); + FunctionPass *createMSP430BranchSelectionPass(); + extern Target TheMSP430Target; } // end namespace llvm; diff --git a/lib/Target/MSP430/MSP430BranchSelector.cpp b/lib/Target/MSP430/MSP430BranchSelector.cpp new file mode 100644 index 00000000000..836e4250aba --- /dev/null +++ b/lib/Target/MSP430/MSP430BranchSelector.cpp @@ -0,0 +1,179 @@ +//===-- MSP430BranchSelector.cpp - Emit long conditional branches--*- C++ -*-=// +// +// The LLVM Compiler Infrastructure +// +// This file is distributed under the University of Illinois Open Source +// License. See LICENSE.TXT for details. +// +//===----------------------------------------------------------------------===// +// +// This file contains a pass that scans a machine function to determine which +// conditional branches need more than 10 bits of displacement to reach their +// target basic block. It does this in two passes; a calculation of basic block +// positions pass, and a branch psuedo op to machine branch opcode pass. This +// pass should be run last, just before the assembly printer. +// +//===----------------------------------------------------------------------===// + +#define DEBUG_TYPE "msp430-branch-select" +#include "MSP430.h" +#include "MSP430InstrInfo.h" +#include "llvm/CodeGen/MachineInstrBuilder.h" +#include "llvm/CodeGen/MachineFunctionPass.h" +#include "llvm/Target/TargetMachine.h" +#include "llvm/ADT/Statistic.h" +#include "llvm/Support/MathExtras.h" +using namespace llvm; + +STATISTIC(NumExpanded, "Number of branches expanded to long format"); + +namespace { + struct MSP430BSel : public MachineFunctionPass { + static char ID; + MSP430BSel() : MachineFunctionPass(&ID) {} + + /// BlockSizes - The sizes of the basic blocks in the function. + std::vector BlockSizes; + + virtual bool runOnMachineFunction(MachineFunction &Fn); + + virtual const char *getPassName() const { + return "MSP430 Branch Selector"; + } + }; + char MSP430BSel::ID = 0; +} + +/// createMSP430BranchSelectionPass - returns an instance of the Branch +/// Selection Pass +/// +FunctionPass *llvm::createMSP430BranchSelectionPass() { + return new MSP430BSel(); +} + +bool MSP430BSel::runOnMachineFunction(MachineFunction &Fn) { + const TargetInstrInfo *TII = Fn.getTarget().getInstrInfo(); + // 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; + + unsigned BlockSize = 0; + for (MachineBasicBlock::iterator MBBI = MBB->begin(), EE = MBB->end(); + MBBI != EE; ++MBBI) + BlockSize += TII->GetInstSizeInBytes(MBBI); + + BlockSizes[MBB->getNumber()] = BlockSize; + FuncSize += BlockSize; + } + + // 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 << 9)) { + BlockSizes.clear(); + return false; + } + + // 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+6 + // b MBB + // + 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() != MSP430::JCC || I->getOperand(0).isImm()) && + I->getOpcode() != MSP430::JMP) { + MBBStartOffset += TII->GetInstSizeInBytes(I); + continue; + } + + // Determine the offset from the current branch to the destination + // block. + MachineBasicBlock *Dest = I->getOperand(0).getMBB(); + + 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]; + } + + // If this branch is in range, ignore it. + if (isInt<10>(BranchSize)) { + MBBStartOffset += 2; + continue; + } + + // Otherwise, we have to expand it to a long branch. + unsigned NewSize; + MachineInstr *OldBranch = I; + DebugLoc dl = OldBranch->getDebugLoc(); + + if (I->getOpcode() == MSP430::JMP) { + NewSize = 4; + } else { + // The BCC operands are: + // 0. MSP430 branch predicate + // 1. Target MBB + SmallVector Cond; + Cond.push_back(I->getOperand(1)); + + // Jump over the uncond branch inst (i.e. $+6) on opposite condition. + TII->ReverseBranchCondition(Cond); + BuildMI(MBB, I, dl, TII->get(MSP430::JCC)) + .addImm(4).addOperand(Cond[0]); + + NewSize = 6; + } + // Uncond branch to the real destination. + I = BuildMI(MBB, I, dl, TII->get(MSP430::B)).addMBB(Dest); + + // Remove the old branch from the function. + OldBranch->eraseFromParent(); + + // Remember that this instruction is NewSize bytes, increase the size of the + // block by NewSize-2, remember to iterate. + BlockSizes[MBB.getNumber()] += NewSize-2; + MBBStartOffset += NewSize; + + ++NumExpanded; + MadeChange = true; + } + } + EverMadeChange |= MadeChange; + } + + BlockSizes.clear(); + return true; +} diff --git a/lib/Target/MSP430/MSP430InstrInfo.cpp b/lib/Target/MSP430/MSP430InstrInfo.cpp index 2ae675999dc..9dc69e0dc77 100644 --- a/lib/Target/MSP430/MSP430InstrInfo.cpp +++ b/lib/Target/MSP430/MSP430InstrInfo.cpp @@ -344,3 +344,45 @@ MSP430InstrInfo::InsertBranch(MachineBasicBlock &MBB, MachineBasicBlock *TBB, } return Count; } + +/// GetInstSize - Return the number of bytes of code the specified +/// instruction may be. This returns the maximum number of bytes. +/// +unsigned MSP430InstrInfo::GetInstSizeInBytes(const MachineInstr *MI) const { + const TargetInstrDesc &Desc = MI->getDesc(); + + switch (Desc.TSFlags & MSP430II::SizeMask) { + default: + switch (Desc.getOpcode()) { + default: + assert(0 && "Unknown instruction size!"); + case TargetInstrInfo::DBG_LABEL: + case TargetInstrInfo::EH_LABEL: + case TargetInstrInfo::IMPLICIT_DEF: + case TargetInstrInfo::KILL: + return 0; + case TargetInstrInfo::INLINEASM: { + const MachineFunction *MF = MI->getParent()->getParent(); + const TargetInstrInfo &TII = *MF->getTarget().getInstrInfo(); + return TII.getInlineAsmLength(MI->getOperand(0).getSymbolName(), + *MF->getTarget().getMCAsmInfo()); + } + } + case MSP430II::SizeSpecial: + switch (MI->getOpcode()) { + default: + assert(0 && "Unknown instruction size!"); + case MSP430::SAR8r1c: + case MSP430::SAR16r1c: + return 4; + } + case MSP430II::Size2Bytes: + return 2; + case MSP430II::Size4Bytes: + return 4; + case MSP430II::Size6Bytes: + return 6; + } + + return 6; +} diff --git a/lib/Target/MSP430/MSP430InstrInfo.h b/lib/Target/MSP430/MSP430InstrInfo.h index e4ceeb9ca7c..6ef4b0a28a2 100644 --- a/lib/Target/MSP430/MSP430InstrInfo.h +++ b/lib/Target/MSP430/MSP430InstrInfo.h @@ -21,6 +21,22 @@ namespace llvm { class MSP430TargetMachine; +/// MSP430II - This namespace holds all of the target specific flags that +/// instruction info tracks. +/// +namespace MSP430II { + enum { + SizeShift = 2, + SizeMask = 7 << SizeShift, + + SizeUnknown = 0 << SizeShift, + SizeSpecial = 1 << SizeShift, + Size2Bytes = 2 << SizeShift, + Size4Bytes = 3 << SizeShift, + Size6Bytes = 4 << SizeShift + }; +} + class MSP430InstrInfo : public TargetInstrInfoImpl { const MSP430RegisterInfo RI; MSP430TargetMachine &TM; @@ -59,6 +75,8 @@ public: MachineBasicBlock::iterator MI, const std::vector &CSI) const; + unsigned GetInstSizeInBytes(const MachineInstr *MI) const; + // Branch folding goodness bool ReverseBranchCondition(SmallVectorImpl &Cond) const; bool isUnpredicatedTerminator(const MachineInstr *MI) const; diff --git a/lib/Target/MSP430/MSP430InstrInfo.td b/lib/Target/MSP430/MSP430InstrInfo.td index bcebff7f09d..cd502cf2be6 100644 --- a/lib/Target/MSP430/MSP430InstrInfo.td +++ b/lib/Target/MSP430/MSP430InstrInfo.td @@ -167,11 +167,18 @@ let isBranch = 1, isTerminator = 1 in { // FIXME: expand opcode & cond field for branches! // Direct branch -let isBarrier = 1 in +let isBarrier = 1 in { + // Short branch def JMP : CJForm<0, 0, (outs), (ins brtarget:$dst), "jmp\t$dst", [(br bb:$dst)]>; + // Long branch + def B : I16ri<0, + (outs), (ins brtarget:$dst), + "br\t$dst", + []>; +} // Conditional branches let Uses = [SRW] in diff --git a/lib/Target/MSP430/MSP430TargetMachine.cpp b/lib/Target/MSP430/MSP430TargetMachine.cpp index 14db406edc9..a0dbac21f5e 100644 --- a/lib/Target/MSP430/MSP430TargetMachine.cpp +++ b/lib/Target/MSP430/MSP430TargetMachine.cpp @@ -44,3 +44,9 @@ bool MSP430TargetMachine::addInstSelector(PassManagerBase &PM, return false; } +bool MSP430TargetMachine::addPreEmitPass(PassManagerBase &PM, + CodeGenOpt::Level OptLevel) { + // Must run branch selection immediately preceding the asm printer. + PM.add(createMSP430BranchSelectionPass()); + return false; +} diff --git a/lib/Target/MSP430/MSP430TargetMachine.h b/lib/Target/MSP430/MSP430TargetMachine.h index d38614018c8..d93ac5c6efe 100644 --- a/lib/Target/MSP430/MSP430TargetMachine.h +++ b/lib/Target/MSP430/MSP430TargetMachine.h @@ -55,6 +55,7 @@ public: } virtual bool addInstSelector(PassManagerBase &PM, CodeGenOpt::Level OptLevel); + virtual bool addPreEmitPass(PassManagerBase &PM, CodeGenOpt::Level OptLevel); }; // MSP430TargetMachine. } // end namespace llvm