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Implement a more intelligent way of spilling uses across an invoke boundary. 

The old way of determine when and where to spill a value that was used inside of
a landing pad resulted in spilling that value everywhere and not just at the
invoke edge.

This algorithm determines which values are used within a landing pad. It then
spills those values before the invoke and reloads them before the uses. This
should prevent excessive spilling in many cases, e.g. inside of loops.
<rdar://problem/10609139>

llvm-svn: 152486
This commit is contained in:
Bill Wendling 2012-03-10 07:11:55 +00:00
parent d2f7007e09
commit 1ab79c6db3
1 changed files with 82 additions and 32 deletions
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114
llvm/lib/CodeGen/SjLjEHPrepare.cpp
View File

@ -21,6 +21,7 @@
#include "llvm/LLVMContext.h"
#include "llvm/Module.h"
#include "llvm/Pass.h"
#include "llvm/Analysis/Verifier.h"
#include "llvm/CodeGen/Passes.h"
#include "llvm/Target/TargetData.h"
#include "llvm/Target/TargetLowering.h"
@ -139,14 +140,19 @@ void SjLjEHPass::insertCallSiteStore(Instruction *I, int Number) {
Builder.CreateStore(CallSiteNoC, CallSite, true/*volatile*/);
}
/// MarkBlocksLiveIn - Insert BB and all of its predescessors into LiveBBs until
/// markBlocksLiveIn - Insert BB and all of its predescessors into LiveBBs until
/// we reach blocks we've already seen.
static void MarkBlocksLiveIn(BasicBlock *BB,
SmallPtrSet<BasicBlock*, 64> &LiveBBs) {
static void markBlocksLiveIn(BasicBlock *BB, Instruction *Inst,
SmallPtrSet<BasicBlock*, 64> &LiveBBs,
SmallPtrSet<BasicBlock*, 4> &InvokesCrossed) {
if (!LiveBBs.insert(BB)) return; // already been here.
for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
MarkBlocksLiveIn(*PI, LiveBBs);
for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
BasicBlock *Pred = *PI;
if (BB->isLandingPad() && BB != Inst->getParent())
InvokesCrossed.insert(Pred);
markBlocksLiveIn(Pred, Inst, LiveBBs, InvokesCrossed);
}
}
/// substituteLPadValues - Substitute the values returned by the landingpad
@ -297,6 +303,9 @@ void SjLjEHPass::lowerIncomingArguments(Function &F) {
/// edge and spill them.
void SjLjEHPass::lowerAcrossUnwindEdges(Function &F,
ArrayRef<InvokeInst*> Invokes) {
SmallVector<std::pair<Instruction*, Instruction*>, 32> ReloadUsers;
DenseMap<std::pair<Instruction*, Instruction*>, AllocaInst*> AllocaMap;
// Finally, scan the code looking for instructions with bad live ranges.
for (Function::iterator
BB = F.begin(), BBE = F.end(); BB != BBE; ++BB) {
@ -327,46 +336,83 @@ void SjLjEHPass::lowerAcrossUnwindEdges(Function &F,
}
// Find all of the blocks that this value is live in.
SmallPtrSet<BasicBlock*, 64> LiveBBs;
LiveBBs.insert(Inst->getParent());
std::map<Instruction*, SmallPtrSet<BasicBlock*, 4> > InvokesCrossed;
std::map<Instruction*, SmallPtrSet<BasicBlock*, 64> > LiveBBs;
while (!Users.empty()) {
Instruction *U = Users.back();
Users.pop_back();
Instruction *U = Users.pop_back_val();
LiveBBs[U].insert(Inst->getParent());
if (!isa<PHINode>(U)) {
MarkBlocksLiveIn(U->getParent(), LiveBBs);
} else {
if (PHINode *PN = dyn_cast<PHINode>(U)) {
// Uses for a PHI node occur in their predecessor block.
PHINode *PN = cast<PHINode>(U);
for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
if (PN->getIncomingValue(i) == Inst)
MarkBlocksLiveIn(PN->getIncomingBlock(i), LiveBBs);
markBlocksLiveIn(PN->getIncomingBlock(i), Inst, LiveBBs[U],
InvokesCrossed[U]);
} else {
markBlocksLiveIn(U->getParent(), Inst, LiveBBs[U], InvokesCrossed[U]);
}
}
// Now that we know all of the blocks that this thing is live in, see if
// it includes any of the unwind locations.
bool NeedsSpill = false;
for (unsigned i = 0, e = Invokes.size(); i != e; ++i) {
BasicBlock *UnwindBlock = Invokes[i]->getUnwindDest();
if (UnwindBlock != BB && LiveBBs.count(UnwindBlock)) {
DEBUG(dbgs() << "SJLJ Spill: " << *Inst << " around "
<< UnwindBlock->getName() << "\n");
NeedsSpill = true;
break;
}
}
// Go through the invokes the value crosses and insert a spill right
// before the invoke.
for (std::map<Instruction*, SmallPtrSet<BasicBlock*, 4> >::iterator
MI = InvokesCrossed.begin(), ME = InvokesCrossed.end();
MI != ME; ++MI) {
Instruction *User = MI->first;
SmallPtrSet<BasicBlock*, 4> &Crossings = MI->second;
if (Crossings.empty()) continue;
// If we decided we need a spill, do it.
// FIXME: Spilling this way is overkill, as it forces all uses of
// the value to be reloaded from the stack slot, even those that aren't
// in the unwind blocks. We should be more selective.
if (NeedsSpill) {
DemoteRegToStack(*Inst, true);
ReloadUsers.push_back(std::make_pair(Inst, User));
AllocaInst *&Slot = AllocaMap[std::make_pair(Inst, User)];
if (!Slot)
Slot = new AllocaInst(Inst->getType(), 0,
Inst->getName() + ".reg2mem",
F.getEntryBlock().begin());
for (SmallPtrSet<BasicBlock*, 4>::iterator
CI = Crossings.begin(), CE = Crossings.end(); CI != CE; ++CI) {
new StoreInst(Inst, Slot, (*CI)->getTerminator());
++NumSpilled;
}
}
}
}
// Now go through the instructions which were spilled and replace their uses
// after a crossed invoke with a reload instruction.
for (SmallVectorImpl<std::pair<Instruction*, Instruction*> >::iterator
I = ReloadUsers.begin(), E = ReloadUsers.end(); I != E; ++I) {
Instruction *User = I->second;
AllocaInst *Slot = AllocaMap[*I];
assert(Slot && "A spill slot hasn't been allocated yet!");
if (PHINode *PN = dyn_cast<PHINode>(User)) {
// If this is a PHI node, we can't insert a load of the value before the
// use. Instead insert the load in the predecessor block corresponding to
// the incoming value.
//
// Note that if there are multiple edges from a basic block to this PHI
// node that we cannot have multiple loads. The problem is that the
// resulting PHI node will have multiple values (from each load) coming in
// from the same block, which is illegal SSA form. For this reason, we
// keep track of and reuse loads we insert.
DenseMap<BasicBlock*, Value*> Loads;
for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
if (PN->getIncomingValue(i) == I->first) {
Value *&V = Loads[PN->getIncomingBlock(i)];
if (V == 0)
// Insert the load into the predecessor block
V = new LoadInst(Slot, I->first->getName() + ".reload", true,
PN->getIncomingBlock(i)->getTerminator());
PN->setIncomingValue(i, V);
}
} else {
LoadInst *Reload = new LoadInst(Slot, Slot->getName() + ".reload", User);
User->replaceUsesOfWith(I->first, Reload);
}
}
// Go through the landing pads and remove any PHIs there.
for (unsigned i = 0, e = Invokes.size(); i != e; ++i) {
@ -521,5 +567,9 @@ bool SjLjEHPass::setupEntryBlockAndCallSites(Function &F) {
bool SjLjEHPass::runOnFunction(Function &F) {
bool Res = setupEntryBlockAndCallSites(F);
DEBUG({
if (verifyFunction(F))
report_fatal_error("verifyFunction failed!");
});
return Res;
}