#include "MCTargetDesc/WebAssemblyMCTargetDesc.h"
#include "WebAssemblySubtarget.h"
#include "llvm/ADT/SCCIterator.h"
+#include "llvm/ADT/SetVector.h"
+#include "llvm/CodeGen/MachineDominators.h"
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/MachineLoopInfo.h"
void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.setPreservesCFG();
+ AU.addRequired<MachineDominatorTree>();
+ AU.addPreserved<MachineDominatorTree>();
AU.addRequired<MachineLoopInfo>();
AU.addPreserved<MachineLoopInfo>();
MachineFunctionPass::getAnalysisUsage(AU);
};
} // end anonymous namespace
+static bool LoopContains(const MachineLoop *Loop,
+ const MachineBasicBlock *MBB) {
+ return Loop ? Loop->contains(MBB) : true;
+}
+
POStackEntry::POStackEntry(MachineBasicBlock *MBB, MachineFunction &MF,
const MachineLoopInfo &MLI)
: MBB(MBB), Succs(MBB->successors()) {
// Keep loops contiguous by preferring the block that's in the same
// loop.
- MachineLoop *LoopA = MLI.getLoopFor(A);
- MachineLoop *LoopB = MLI.getLoopFor(B);
- if (LoopA == Loop && LoopB != Loop)
+ bool LoopContainsA = LoopContains(Loop, A);
+ bool LoopContainsB = LoopContains(Loop, B);
+ if (LoopContainsA && !LoopContainsB)
return true;
- if (LoopA != Loop && LoopB == Loop)
+ if (!LoopContainsA && LoopContainsB)
return false;
// Minimize perturbation by preferring the block which is the immediate
});
}
+/// Return the "bottom" block of a loop. This differs from
+/// MachineLoop::getBottomBlock in that it works even if the loop is
+/// discontiguous.
+static MachineBasicBlock *LoopBottom(const MachineLoop *Loop) {
+ MachineBasicBlock *Bottom = Loop->getHeader();
+ for (MachineBasicBlock *MBB : Loop->blocks())
+ if (MBB->getNumber() > Bottom->getNumber())
+ Bottom = MBB;
+ return Bottom;
+}
+
/// Sort the blocks in RPO, taking special care to make sure that loops are
/// contiguous even in the case of split backedges.
+///
+/// TODO: Determine whether RPO is actually worthwhile, or whether we should
+/// move to just a stable-topological-sort-based approach that would preserve
+/// more of the original order.
static void SortBlocks(MachineFunction &MF, const MachineLoopInfo &MLI) {
// Note that we do our own RPO rather than using
// "llvm/ADT/PostOrderIterator.h" because we want control over the order that
SmallPtrSet<MachineBasicBlock *, 16> Visited;
SmallVector<POStackEntry, 16> Stack;
- MachineBasicBlock *Entry = &*MF.begin();
- Visited.insert(Entry);
- Stack.push_back(POStackEntry(Entry, MF, MLI));
+ MachineBasicBlock *EntryBlock = &*MF.begin();
+ Visited.insert(EntryBlock);
+ Stack.push_back(POStackEntry(EntryBlock, MF, MLI));
for (;;) {
POStackEntry &Entry = Stack.back();
MF.RenumberBlocks();
#ifndef NDEBUG
- for (auto &MBB : MF)
- if (MachineLoop *Loop = MLI.getLoopFor(&MBB)) {
- // Assert that loops are contiguous.
- assert(Loop->getHeader() == Loop->getTopBlock());
- assert((Loop->getHeader() == &MBB ||
- Loop->contains(
- MLI.getLoopFor(&*prev(MachineFunction::iterator(&MBB))))) &&
- "Loop isn't contiguous");
+ SmallSetVector<MachineLoop *, 8> OnStack;
+
+ // Insert a sentinel representing the degenerate loop that starts at the
+ // function entry block and includes the entire function as a "loop" that
+ // executes once.
+ OnStack.insert(nullptr);
+
+ for (auto &MBB : MF) {
+ assert(MBB.getNumber() >= 0 && "Renumbered blocks should be non-negative.");
+
+ MachineLoop *Loop = MLI.getLoopFor(&MBB);
+ if (Loop && &MBB == Loop->getHeader()) {
+ // Loop header. The loop predecessor should be sorted above, and the other
+ // predecessors should be backedges below.
+ for (auto Pred : MBB.predecessors())
+ assert(
+ (Pred->getNumber() < MBB.getNumber() || Loop->contains(Pred)) &&
+ "Loop header predecessors must be loop predecessors or backedges");
+ assert(OnStack.insert(Loop) && "Loops should be declared at most once.");
} else {
- // Assert that non-loops have no backedge predecessors.
+ // Not a loop header. All predecessors should be sorted above.
for (auto Pred : MBB.predecessors())
assert(Pred->getNumber() < MBB.getNumber() &&
- "CFG still has multiple-entry loops");
+ "Non-loop-header predecessors should be topologically sorted");
+ assert(OnStack.count(MLI.getLoopFor(&MBB)) &&
+ "Blocks must be nested in their loops");
}
+ while (OnStack.size() > 1 && &MBB == LoopBottom(OnStack.back()))
+ OnStack.pop_back();
+ }
+ assert(OnStack.pop_back_val() == nullptr &&
+ "The function entry block shouldn't actually be a loop header");
+ assert(OnStack.empty() &&
+ "Control flow stack pushes and pops should be balanced.");
#endif
}
-/// Insert BLOCK markers at appropriate places.
-static void PlaceBlockMarkers(MachineBasicBlock &MBB, MachineBasicBlock &Succ,
- MachineFunction &MF, const MachineLoopInfo &MLI,
- const WebAssemblyInstrInfo &TII) {
- // Backward branches are loop backedges, and we place the LOOP markers
- // separately. So only consider forward branches here.
- if (Succ.getNumber() <= MBB.getNumber())
+/// Insert a BLOCK marker for branches to MBB (if needed).
+static void PlaceBlockMarker(MachineBasicBlock &MBB, MachineFunction &MF,
+ SmallVectorImpl<MachineBasicBlock *> &ScopeTops,
+ const WebAssemblyInstrInfo &TII,
+ const MachineLoopInfo &MLI,
+ MachineDominatorTree &MDT) {
+ // First compute the nearest common dominator of all forward non-fallthrough
+ // predecessors so that we minimize the time that the BLOCK is on the stack,
+ // which reduces overall stack height.
+ MachineBasicBlock *Header = nullptr;
+ bool IsBranchedTo = false;
+ int MBBNumber = MBB.getNumber();
+ for (MachineBasicBlock *Pred : MBB.predecessors())
+ if (Pred->getNumber() < MBBNumber) {
+ Header = Header ? MDT.findNearestCommonDominator(Header, Pred) : Pred;
+ if (!Pred->isLayoutSuccessor(&MBB) ||
+ !(Pred->empty() || !Pred->back().isBarrier()))
+ IsBranchedTo = true;
+ }
+ if (!Header)
+ return;
+ if (!IsBranchedTo)
return;
- // Place the BLOCK for a forward branch. For simplicity, we just insert
- // blocks immediately inside loop boundaries.
- MachineLoop *Loop = MLI.getLoopFor(&Succ);
- MachineBasicBlock &Header = *(Loop ? Loop->getHeader() : &MF.front());
- MachineBasicBlock::iterator InsertPos = Header.begin(), End = Header.end();
- if (InsertPos != End) {
- if (InsertPos->getOpcode() == WebAssembly::LOOP)
- ++InsertPos;
- int SuccNumber = Succ.getNumber();
- // Position the BLOCK in nesting order.
- for (; InsertPos != End && InsertPos->getOpcode() == WebAssembly::BLOCK;
- ++InsertPos) {
- int N = InsertPos->getOperand(0).getMBB()->getNumber();
- if (N < SuccNumber)
+ assert(&MBB != &MF.front() && "Header blocks shouldn't have predecessors");
+ MachineBasicBlock *LayoutPred = &*prev(MachineFunction::iterator(&MBB));
+
+ // If the nearest common dominator is inside a more deeply nested context,
+ // walk out to the nearest scope which isn't more deeply nested.
+ for (MachineFunction::iterator I(LayoutPred), E(Header); I != E; --I) {
+ if (MachineBasicBlock *ScopeTop = ScopeTops[I->getNumber()]) {
+ if (ScopeTop->getNumber() > Header->getNumber()) {
+ // Skip over an intervening scope.
+ I = next(MachineFunction::iterator(ScopeTop));
+ } else {
+ // We found a scope level at an appropriate depth.
+ Header = ScopeTop;
break;
- // If there's already a BLOCK for Succ, we don't need another.
- if (N == SuccNumber)
- return;
+ }
}
}
- BuildMI(Header, InsertPos, DebugLoc(), TII.get(WebAssembly::BLOCK))
- .addMBB(&Succ);
+ // If there's a loop which ends just before MBB which contains Header, we can
+ // reuse its label instead of inserting a new BLOCK.
+ for (MachineLoop *Loop = MLI.getLoopFor(LayoutPred);
+ Loop && Loop->contains(LayoutPred); Loop = Loop->getParentLoop())
+ if (Loop && LoopBottom(Loop) == LayoutPred && Loop->contains(Header))
+ return;
+
+ // Decide where in Header to put the BLOCK.
+ MachineBasicBlock::iterator InsertPos;
+ MachineLoop *HeaderLoop = MLI.getLoopFor(Header);
+ if (HeaderLoop && MBB.getNumber() > LoopBottom(HeaderLoop)->getNumber()) {
+ // Header is the header of a loop that does not lexically contain MBB, so
+ // the BLOCK needs to be above the LOOP.
+ InsertPos = Header->begin();
+ } else {
+ // Otherwise, insert the BLOCK as late in Header as we can, but before any
+ // existing BLOCKs.
+ InsertPos = Header->getFirstTerminator();
+ while (InsertPos != Header->begin() &&
+ prev(InsertPos)->getOpcode() == WebAssembly::BLOCK)
+ --InsertPos;
+ }
+
+ // Add the BLOCK.
+ BuildMI(*Header, InsertPos, DebugLoc(), TII.get(WebAssembly::BLOCK))
+ .addMBB(&MBB);
+
+ // Track the farthest-spanning scope that ends at this point.
+ int Number = MBB.getNumber();
+ if (!ScopeTops[Number] ||
+ ScopeTops[Number]->getNumber() > Header->getNumber())
+ ScopeTops[Number] = Header;
+}
+
+/// Insert a LOOP marker for a loop starting at MBB (if it's a loop header).
+static void PlaceLoopMarker(MachineBasicBlock &MBB, MachineFunction &MF,
+ SmallVectorImpl<MachineBasicBlock *> &ScopeTops,
+ const WebAssemblyInstrInfo &TII,
+ const MachineLoopInfo &MLI) {
+ MachineLoop *Loop = MLI.getLoopFor(&MBB);
+ if (!Loop || Loop->getHeader() != &MBB)
+ return;
+
+ // The operand of a LOOP is the first block after the loop. If the loop is the
+ // bottom of the function, insert a dummy block at the end.
+ MachineBasicBlock *Bottom = LoopBottom(Loop);
+ auto Iter = next(MachineFunction::iterator(Bottom));
+ if (Iter == MF.end()) {
+ MachineBasicBlock *Label = MF.CreateMachineBasicBlock();
+ // Give it a fake predecessor so that AsmPrinter prints its label.
+ Label->addSuccessor(Label);
+ MF.push_back(Label);
+ Iter = next(MachineFunction::iterator(Bottom));
+ }
+ MachineBasicBlock *AfterLoop = &*Iter;
+ BuildMI(MBB, MBB.begin(), DebugLoc(), TII.get(WebAssembly::LOOP))
+ .addMBB(AfterLoop);
+
+ // Emit a special no-op telling the asm printer that we need a label to close
+ // the loop scope, even though the destination is only reachable by
+ // fallthrough.
+ if (!Bottom->back().isBarrier())
+ BuildMI(*Bottom, Bottom->end(), DebugLoc(), TII.get(WebAssembly::LOOP_END));
+
+ assert((!ScopeTops[AfterLoop->getNumber()] ||
+ ScopeTops[AfterLoop->getNumber()]->getNumber() < MBB.getNumber()) &&
+ "With RPO we should visit the outer-most loop for a block first.");
+ if (!ScopeTops[AfterLoop->getNumber()])
+ ScopeTops[AfterLoop->getNumber()] = &MBB;
}
/// Insert LOOP and BLOCK markers at appropriate places.
static void PlaceMarkers(MachineFunction &MF, const MachineLoopInfo &MLI,
- const WebAssemblyInstrInfo &TII) {
+ const WebAssemblyInstrInfo &TII,
+ MachineDominatorTree &MDT) {
+ // For each block whose label represents the end of a scope, record the block
+ // which holds the beginning of the scope. This will allow us to quickly skip
+ // over scoped regions when walking blocks. We allocate one more than the
+ // number of blocks in the function to accommodate for the possible fake block
+ // we may insert at the end.
+ SmallVector<MachineBasicBlock *, 8> ScopeTops(MF.getNumBlockIDs() + 1);
+
for (auto &MBB : MF) {
- // Place the LOOP for loops.
- if (MachineLoop *Loop = MLI.getLoopFor(&MBB))
- if (Loop->getHeader() == &MBB) {
- // The operand of a LOOP is the first block after the loop. If the loop
- // is the bottom of the function, insert a dummy block at the end.
- MachineBasicBlock *Bottom = Loop->getBottomBlock();
- auto Iter = next(MachineFunction::iterator(Bottom));
- if (Iter == MF.end()) {
- MF.push_back(MF.CreateMachineBasicBlock());
- Iter = next(MachineFunction::iterator(Bottom));
- }
- BuildMI(MBB, MBB.begin(), DebugLoc(), TII.get(WebAssembly::LOOP))
- .addMBB(&*Iter);
- }
+ // Place the LOOP for MBB if MBB is the header of a loop.
+ PlaceLoopMarker(MBB, MF, ScopeTops, TII, MLI);
- // Check for forward branches and switches that need BLOCKS placed.
- for (auto &Term : MBB.terminators())
- for (auto &MO : Term.operands())
- if (MO.isMBB())
- PlaceBlockMarkers(MBB, *MO.getMBB(), MF, MLI, TII);
+ // Place the BLOCK for MBB if MBB is branched to from above.
+ PlaceBlockMarker(MBB, MF, ScopeTops, TII, MLI, MDT);
}
}
+#ifndef NDEBUG
+static bool
+IsOnStack(const SmallVectorImpl<std::pair<MachineBasicBlock *, bool>> &Stack,
+ const MachineBasicBlock *MBB) {
+ for (const auto &Pair : Stack)
+ if (Pair.first == MBB)
+ return true;
+ return false;
+}
+#endif
+
bool WebAssemblyCFGStackify::runOnMachineFunction(MachineFunction &MF) {
DEBUG(dbgs() << "********** CFG Stackifying **********\n"
"********** Function: "
<< MF.getName() << '\n');
const auto &MLI = getAnalysis<MachineLoopInfo>();
+ auto &MDT = getAnalysis<MachineDominatorTree>();
const auto &TII = *MF.getSubtarget<WebAssemblySubtarget>().getInstrInfo();
// RPO sorting needs all loops to be single-entry.
SortBlocks(MF, MLI);
// Place the BLOCK and LOOP markers to indicate the beginnings of scopes.
- PlaceMarkers(MF, MLI, TII);
+ PlaceMarkers(MF, MLI, TII, MDT);
+
+#ifndef NDEBUG
+ // Verify that block and loop beginnings and endings are in LIFO order, and
+ // that all references to blocks are to blocks on the stack at the point of
+ // the reference.
+ SmallVector<std::pair<MachineBasicBlock *, bool>, 0> Stack;
+ for (auto &MBB : MF) {
+ while (!Stack.empty() && Stack.back().first == &MBB)
+ if (Stack.back().second) {
+ assert(Stack.size() >= 2);
+ Stack.pop_back();
+ Stack.pop_back();
+ } else {
+ assert(Stack.size() >= 1);
+ Stack.pop_back();
+ }
+ for (auto &MI : MBB)
+ switch (MI.getOpcode()) {
+ case WebAssembly::LOOP:
+ Stack.push_back(std::make_pair(&MBB, false));
+ Stack.push_back(std::make_pair(MI.getOperand(0).getMBB(), true));
+ break;
+ case WebAssembly::BLOCK:
+ Stack.push_back(std::make_pair(MI.getOperand(0).getMBB(), false));
+ break;
+ default:
+ // Verify that all referenced blocks are in scope. A reference to a
+ // block with a negative number is invalid, but can happen with inline
+ // asm, so we shouldn't assert on it, but instead let CodeGen properly
+ // fail on it.
+ for (const MachineOperand &MO : MI.explicit_operands())
+ if (MO.isMBB() && MO.getMBB()->getNumber() >= 0)
+ assert(IsOnStack(Stack, MO.getMBB()));
+ break;
+ }
+ }
+ assert(Stack.empty());
+#endif
return true;
}
projects / oota-llvm.git / blobdiff