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MachineRegisterInfo: Remove UsedPhysReg infrastructure

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We have a detailed def/use lists for every physical register in
MachineRegisterInfo anyway, so there is little use in maintaining an
additional bitset of which ones are used.

Removing it frees us from extra book keeping. This simplifies
VirtRegMap.

Differential Revision: http://reviews.llvm.org/D10911

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@242173 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Matthias Braun
2015-07-14 17:52:07 +00:00
parent 230c4739b3
commit 2addf067a2
18 changed files with 23 additions and 179 deletions
Download Patch File Download Diff File Expand all files Collapse all files

73
lib/CodeGen/VirtRegMap.cpp
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@ -163,7 +163,6 @@ class VirtRegRewriter : public MachineFunctionPass {
SlotIndexes *Indexes;
LiveIntervals *LIS;
VirtRegMap *VRM;
SparseSet<unsigned> PhysRegs;
void rewrite();
void addMBBLiveIns();
@ -319,54 +318,15 @@ void VirtRegRewriter::rewrite() {
SmallVector<unsigned, 8> SuperDeads;
SmallVector<unsigned, 8> SuperDefs;
SmallVector<unsigned, 8> SuperKills;
SmallPtrSet<const MachineInstr *, 4> NoReturnInsts;
// Here we have a SparseSet to hold which PhysRegs are actually encountered
// in the MF we are about to iterate over so that later when we call
// setPhysRegUsed, we are only doing it for physRegs that were actually found
// in the program and not for all of the possible physRegs for the given
// target architecture. If the target has a lot of physRegs, then for a small
// program there will be a significant compile time reduction here.
PhysRegs.clear();
PhysRegs.setUniverse(TRI->getNumRegs());
// The function with uwtable should guarantee that the stack unwinder
// can unwind the stack to the previous frame. Thus, we can't apply the
// noreturn optimization if the caller function has uwtable attribute.
bool HasUWTable = MF->getFunction()->hasFnAttribute(Attribute::UWTable);
for (MachineFunction::iterator MBBI = MF->begin(), MBBE = MF->end();
MBBI != MBBE; ++MBBI) {
DEBUG(MBBI->print(dbgs(), Indexes));
bool IsExitBB = MBBI->succ_empty();
for (MachineBasicBlock::instr_iterator
MII = MBBI->instr_begin(), MIE = MBBI->instr_end(); MII != MIE;) {
MachineInstr *MI = MII;
++MII;
// Check if this instruction is a call to a noreturn function. If this
// is a call to noreturn function and we don't need the stack unwinding
// functionality (i.e. this function does not have uwtable attribute and
// the callee function has the nounwind attribute), then we can ignore
// the definitions set by this instruction.
if (!HasUWTable && IsExitBB && MI->isCall()) {
for (MachineInstr::mop_iterator MOI = MI->operands_begin(),
MOE = MI->operands_end(); MOI != MOE; ++MOI) {
MachineOperand &MO = *MOI;
if (!MO.isGlobal())
continue;
const Function *Func = dyn_cast<Function>(MO.getGlobal());
if (!Func || !Func->hasFnAttribute(Attribute::NoReturn) ||
// We need to keep correct unwind information
// even if the function will not return, since the
// runtime may need it.
!Func->hasFnAttribute(Attribute::NoUnwind))
continue;
NoReturnInsts.insert(MI);
break;
}
}
for (MachineInstr::mop_iterator MOI = MI->operands_begin(),
MOE = MI->operands_end(); MOI != MOE; ++MOI) {
MachineOperand &MO = *MOI;
@ -375,15 +335,6 @@ void VirtRegRewriter::rewrite() {
if (MO.isRegMask())
MRI->addPhysRegsUsedFromRegMask(MO.getRegMask());
// If we encounter a VirtReg or PhysReg then get at the PhysReg and add
// it to the physreg bitset. Later we use only the PhysRegs that were
// actually encountered in the MF to populate the MRI's used physregs.
if (MO.isReg() && MO.getReg())
PhysRegs.insert(
TargetRegisterInfo::isVirtualRegister(MO.getReg()) ?
VRM->getPhys(MO.getReg()) :
MO.getReg());
if (!MO.isReg() || !TargetRegisterInfo::isVirtualRegister(MO.getReg()))
continue;
unsigned VirtReg = MO.getReg();
@ -470,29 +421,5 @@ void VirtRegRewriter::rewrite() {
}
}
}
// Tell MRI about physical registers in use.
if (NoReturnInsts.empty()) {
for (SparseSet<unsigned>::iterator
RegI = PhysRegs.begin(), E = PhysRegs.end(); RegI != E; ++RegI)
if (!MRI->reg_nodbg_empty(*RegI))
MRI->setPhysRegUsed(*RegI);
} else {
for (SparseSet<unsigned>::iterator
I = PhysRegs.begin(), E = PhysRegs.end(); I != E; ++I) {
unsigned Reg = *I;
if (MRI->reg_nodbg_empty(Reg))
continue;
// Check if this register has a use that will impact the rest of the
// code. Uses in debug and noreturn instructions do not impact the
// generated code.
for (MachineInstr &It : MRI->reg_nodbg_instructions(Reg)) {
if (!NoReturnInsts.count(&It)) {
MRI->setPhysRegUsed(Reg);
break;
}
}
}
}
}