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Add comment; refactor; avoid pulling in DT if it's not used.

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@93306 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Evan Cheng 2010-01-13 07:59:13 +00:00
parent ee9250bb4f
commit d89d5180d1
1 changed files with 114 additions and 83 deletions
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63
lib/CodeGen/OptimizeExts.cpp
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@ -6,6 +6,16 @@
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This pass performs optimization of sign / zero extension instructions. It
// may be extended to handle other instructions of similar property.
//
// On some targets, some instructions, e.g. X86 sign / zero extension, may
// leave the source value in the lower part of the result. This pass will
// replace (some) uses of the pre-extension value with uses of the sub-register
// of the results.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "ext-opt"
#include "llvm/CodeGen/Passes.h"
@ -40,9 +50,15 @@ namespace {
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
AU.setPreservesCFG();
MachineFunctionPass::getAnalysisUsage(AU);
if (Aggressive) {
AU.addRequired<MachineDominatorTree>();
AU.addPreserved<MachineDominatorTree>();
}
}
private:
bool OptimizeInstr(MachineInstr *MI, MachineBasicBlock *MBB,
SmallPtrSet<MachineInstr*, 8> &LocalMIs);
};
}
@ -52,36 +68,29 @@ X("opt-exts", "Optimize sign / zero extensions");
FunctionPass *llvm::createOptimizeExtsPass() { return new OptimizeExts(); }
bool OptimizeExts::runOnMachineFunction(MachineFunction &MF) {
TM = &MF.getTarget();
TII = TM->getInstrInfo();
MRI = &MF.getRegInfo();
DT = &getAnalysis<MachineDominatorTree>();
/// OptimizeInstr - If instruction is a copy-like instruction, i.e. it reads
/// a single register and writes a single register and it does not modify
/// the source, and if the source value is preserved as a sub-register of
/// the result, then replace all reachable uses of the source with the subreg
/// of the result.
bool OptimizeExts::OptimizeInstr(MachineInstr *MI, MachineBasicBlock *MBB,
SmallPtrSet<MachineInstr*, 8> &LocalMIs) {
bool Changed = false;
SmallPtrSet<MachineInstr*, 8> LocalMIs;
for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I) {
MachineBasicBlock *MBB = &*I;
for (MachineBasicBlock::iterator MII = I->begin(), ME = I->end(); MII != ME;
++MII) {
MachineInstr *MI = &*MII;
LocalMIs.insert(MI);
unsigned SrcReg, DstReg, SubIdx;
if (TII->isCoalescableExtInstr(*MI, SrcReg, DstReg, SubIdx)) {
if (TargetRegisterInfo::isPhysicalRegister(DstReg) ||
TargetRegisterInfo::isPhysicalRegister(SrcReg))
continue;
return false;
MachineRegisterInfo::use_iterator UI = MRI->use_begin(SrcReg);
if (++UI == MRI->use_end())
// No other uses.
continue;
return false;
// Ok, the source has other uses. See if we can replace the other uses
// with use of the result of the extension.
SmallPtrSet<MachineBasicBlock*, 4> ReachedBBs;
UI = MRI->use_begin(DstReg);
for (MachineRegisterInfo::use_iterator UE = MRI->use_end(); UI != UE;
@ -89,7 +98,9 @@ bool OptimizeExts::runOnMachineFunction(MachineFunction &MF) {
ReachedBBs.insert(UI->getParent());
bool ExtendLife = true;
// Uses that are in the same BB of uses of the result of the instruction.
SmallVector<MachineOperand*, 8> Uses;
// Uses that the result of the instruction can reach.
SmallVector<MachineOperand*, 8> ExtendedUses;
UI = MRI->use_begin(SrcReg);
@ -142,6 +153,26 @@ bool OptimizeExts::runOnMachineFunction(MachineFunction &MF) {
}
}
}
return Changed;
}
bool OptimizeExts::runOnMachineFunction(MachineFunction &MF) {
TM = &MF.getTarget();
TII = TM->getInstrInfo();
MRI = &MF.getRegInfo();
DT = Aggressive ? &getAnalysis<MachineDominatorTree>() : 0;
bool Changed = false;
SmallPtrSet<MachineInstr*, 8> LocalMIs;
for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I) {
MachineBasicBlock *MBB = &*I;
LocalMIs.clear();
for (MachineBasicBlock::iterator MII = I->begin(), ME = I->end(); MII != ME;
++MII) {
MachineInstr *MI = &*MII;
Changed |= OptimizeInstr(MI, MBB, LocalMIs);
}
}