[llvm-commits] [llvm] r102034 - /llvm/trunk/lib/CodeGen/RegAllocFast.cpp
Jakob Stoklund Olesen
stoklund at 2pi.dk
Wed Apr 21 16:18:07 PDT 2010
Author: stoklund
Date: Wed Apr 21 18:18:07 2010
New Revision: 102034
URL: http://llvm.org/viewvc/llvm-project?rev=102034&view=rev
Log:
Run LiveVariables instead of computing liveness locally in -regalloc=fast.
This actually makes everything slower, but the plan is to have isel add <kill>
flags the way it is already adding <dead> flags. Then LiveVariables can be
removed again.
When ignoring the time spent in LiveVariables, -regalloc=fast is now twice as
fast as -regalloc=local.
Modified:
llvm/trunk/lib/CodeGen/RegAllocFast.cpp
Modified: llvm/trunk/lib/CodeGen/RegAllocFast.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/RegAllocFast.cpp?rev=102034&r1=102033&r2=102034&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/RegAllocFast.cpp (original)
+++ llvm/trunk/lib/CodeGen/RegAllocFast.cpp Wed Apr 21 18:18:07 2010
@@ -18,6 +18,7 @@
#include "llvm/CodeGen/MachineInstr.h"
#include "llvm/CodeGen/MachineFrameInfo.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
+#include "llvm/CodeGen/LiveVariables.h"
#include "llvm/CodeGen/Passes.h"
#include "llvm/CodeGen/RegAllocRegistry.h"
#include "llvm/Target/TargetInstrInfo.h"
@@ -123,6 +124,7 @@
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
AU.setPreservesCFG();
+ AU.addRequired<LiveVariables>();
AU.addRequiredID(PHIEliminationID);
AU.addRequiredID(TwoAddressInstructionPassID);
MachineFunctionPass::getAnalysisUsage(AU);
@@ -218,10 +220,6 @@
unsigned OpNum, SmallSet<unsigned, 4> &RRegs,
unsigned PhysReg);
- /// ComputeLocalLiveness - Computes liveness of registers within a basic
- /// block, setting the killed/dead flags as appropriate.
- void ComputeLocalLiveness(MachineBasicBlock& MBB);
-
void reloadPhysReg(MachineBasicBlock &MBB, MachineBasicBlock::iterator &I,
unsigned PhysReg);
};
@@ -538,177 +536,6 @@
return false;
}
-// precedes - Helper function to determine with MachineInstr A
-// precedes MachineInstr B within the same MBB.
-static bool precedes(MachineBasicBlock::iterator A,
- MachineBasicBlock::iterator B) {
- if (A == B)
- return false;
-
- MachineBasicBlock::iterator I = A->getParent()->begin();
- while (I != A->getParent()->end()) {
- if (I == A)
- return true;
- else if (I == B)
- return false;
-
- ++I;
- }
-
- return false;
-}
-
-/// ComputeLocalLiveness - Computes liveness of registers within a basic
-/// block, setting the killed/dead flags as appropriate.
-void RAFast::ComputeLocalLiveness(MachineBasicBlock& MBB) {
- MachineRegisterInfo &MRI = MBB.getParent()->getRegInfo();
- // Keep track of the most recently seen previous use or def of each reg,
- // so that we can update them with dead/kill markers.
- DenseMap<unsigned, std::pair<MachineInstr*, unsigned> > LastUseDef;
- for (MachineBasicBlock::iterator I = MBB.begin(), E = MBB.end();
- I != E; ++I) {
- if (I->isDebugValue())
- continue;
-
- for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) {
- MachineOperand &MO = I->getOperand(i);
- // Uses don't trigger any flags, but we need to save
- // them for later. Also, we have to process these
- // _before_ processing the defs, since an instr
- // uses regs before it defs them.
- if (!MO.isReg() || !MO.getReg() || !MO.isUse())
- continue;
-
- LastUseDef[MO.getReg()] = std::make_pair(I, i);
-
- if (TargetRegisterInfo::isVirtualRegister(MO.getReg())) continue;
-
- const unsigned *Aliases = TRI->getAliasSet(MO.getReg());
- if (Aliases == 0)
- continue;
-
- while (*Aliases) {
- DenseMap<unsigned, std::pair<MachineInstr*, unsigned> >::iterator
- alias = LastUseDef.find(*Aliases);
-
- if (alias != LastUseDef.end() && alias->second.first != I)
- LastUseDef[*Aliases] = std::make_pair(I, i);
-
- ++Aliases;
- }
- }
-
- for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) {
- MachineOperand &MO = I->getOperand(i);
- // Defs others than 2-addr redefs _do_ trigger flag changes:
- // - A def followed by a def is dead
- // - A use followed by a def is a kill
- if (!MO.isReg() || !MO.getReg() || !MO.isDef()) continue;
-
- DenseMap<unsigned, std::pair<MachineInstr*, unsigned> >::iterator
- last = LastUseDef.find(MO.getReg());
- if (last != LastUseDef.end()) {
- // Check if this is a two address instruction. If so, then
- // the def does not kill the use.
- if (last->second.first == I &&
- I->isRegTiedToUseOperand(i))
- continue;
-
- MachineOperand &lastUD =
- last->second.first->getOperand(last->second.second);
- if (lastUD.isDef())
- lastUD.setIsDead(true);
- else
- lastUD.setIsKill(true);
- }
-
- LastUseDef[MO.getReg()] = std::make_pair(I, i);
- }
- }
-
- // Live-out (of the function) registers contain return values of the function,
- // so we need to make sure they are alive at return time.
- MachineBasicBlock::iterator Ret = MBB.getFirstTerminator();
- bool BBEndsInReturn = (Ret != MBB.end() && Ret->getDesc().isReturn());
-
- if (BBEndsInReturn)
- for (MachineRegisterInfo::liveout_iterator
- I = MF->getRegInfo().liveout_begin(),
- E = MF->getRegInfo().liveout_end(); I != E; ++I)
- if (!Ret->readsRegister(*I)) {
- Ret->addOperand(MachineOperand::CreateReg(*I, false, true));
- LastUseDef[*I] = std::make_pair(Ret, Ret->getNumOperands()-1);
- }
-
- // Finally, loop over the final use/def of each reg
- // in the block and determine if it is dead.
- for (DenseMap<unsigned, std::pair<MachineInstr*, unsigned> >::iterator
- I = LastUseDef.begin(), E = LastUseDef.end(); I != E; ++I) {
- MachineInstr *MI = I->second.first;
- unsigned idx = I->second.second;
- MachineOperand &MO = MI->getOperand(idx);
-
- bool isPhysReg = TargetRegisterInfo::isPhysicalRegister(MO.getReg());
-
- // A crude approximation of "live-out" calculation
- bool usedOutsideBlock = isPhysReg ? false :
- UsedInMultipleBlocks.test(MO.getReg() -
- TargetRegisterInfo::FirstVirtualRegister);
-
- // If the machine BB ends in a return instruction, then the value isn't used
- // outside of the BB.
- if (!isPhysReg && (!usedOutsideBlock || BBEndsInReturn)) {
- // DBG_VALUE complicates this: if the only refs of a register outside
- // this block are DBG_VALUE, we can't keep the reg live just for that,
- // as it will cause the reg to be spilled at the end of this block when
- // it wouldn't have been otherwise. Nullify the DBG_VALUEs when that
- // happens.
- bool UsedByDebugValueOnly = false;
- for (MachineRegisterInfo::reg_iterator UI = MRI.reg_begin(MO.getReg()),
- UE = MRI.reg_end(); UI != UE; ++UI) {
- // Two cases:
- // - used in another block
- // - used in the same block before it is defined (loop)
- if (UI->getParent() == &MBB &&
- !(MO.isDef() && UI.getOperand().isUse() && precedes(&*UI, MI)))
- continue;
-
- if (UI->isDebugValue()) {
- UsedByDebugValueOnly = true;
- continue;
- }
-
- // A non-DBG_VALUE use means we can leave DBG_VALUE uses alone.
- UsedInMultipleBlocks.set(MO.getReg() -
- TargetRegisterInfo::FirstVirtualRegister);
- usedOutsideBlock = true;
- UsedByDebugValueOnly = false;
- break;
- }
-
- if (UsedByDebugValueOnly)
- for (MachineRegisterInfo::reg_iterator UI = MRI.reg_begin(MO.getReg()),
- UE = MRI.reg_end(); UI != UE; ++UI)
- if (UI->isDebugValue() &&
- (UI->getParent() != &MBB ||
- (MO.isDef() && precedes(&*UI, MI))))
- UI.getOperand().setReg(0U);
- }
-
- // Physical registers and those that are not live-out of the block are
- // killed/dead at their last use/def within this block.
- if (isPhysReg || !usedOutsideBlock || BBEndsInReturn) {
- if (MO.isUse()) {
- // Don't mark uses that are tied to defs as kills.
- if (!MI->isRegTiedToDefOperand(idx))
- MO.setIsKill(true);
- } else {
- MO.setIsDead(true);
- }
- }
- }
-}
-
void RAFast::AllocateBasicBlock(MachineBasicBlock &MBB) {
// loop over each instruction
MachineBasicBlock::iterator MII = MBB.begin();
@@ -733,8 +560,6 @@
}
}
- ComputeLocalLiveness(MBB);
-
// Otherwise, sequentially allocate each instruction in the MBB.
while (MII != MBB.end()) {
MachineInstr *MI = MII++;
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