/// than this number of comparisons.
static const unsigned RuntimeMemoryCheckThreshold = 8;
-/// We use a metadata with this name to indicate that a scalar loop was
-/// vectorized and that we don't need to re-vectorize it if we run into it
-/// again.
-static const char*
-AlreadyVectorizedMDName = "llvm.vectorizer.already_vectorized";
+/// Maximum simd width.
+static const unsigned MaxVectorWidth = 64;
+
+/// Maximum vectorization unroll count.
+static const unsigned MaxUnrollFactor = 16;
namespace {
const TargetLibraryInfo *TLI;
};
+/// Utility class for getting and setting loop vectorizer hints in the form
+/// of loop metadata.
+struct LoopVectorizeHints {
+ /// Vectorization width.
+ unsigned Width;
+ /// Vectorization unroll factor.
+ unsigned Unroll;
+
+ LoopVectorizeHints(const Loop *L)
+ : Width(VectorizationFactor)
+ , Unroll(VectorizationUnroll)
+ , LoopID(L->getLoopID()) {
+ getHints(L);
+ // The command line options override any loop metadata except for when
+ // width == 1 which is used to indicate the loop is already vectorized.
+ if (VectorizationFactor.getNumOccurrences() > 0 && Width != 1)
+ Width = VectorizationFactor;
+ if (VectorizationUnroll.getNumOccurrences() > 0)
+ Unroll = VectorizationUnroll;
+ }
+
+ /// Return the loop vectorizer metadata prefix.
+ static StringRef Prefix() { return "llvm.vectorizer."; }
+
+ MDNode *createHint(LLVMContext &Context, StringRef Name, unsigned V) {
+ SmallVector<Value*, 2> Vals;
+ Vals.push_back(MDString::get(Context, Name));
+ Vals.push_back(ConstantInt::get(Type::getInt32Ty(Context), V));
+ return MDNode::get(Context, Vals);
+ }
+
+ /// Mark the loop L as already vectorized by setting the width to 1.
+ void setAlreadyVectorized(Loop *L) {
+ LLVMContext &Context = L->getHeader()->getContext();
+
+ Width = 1;
+
+ // Create a new loop id with one more operand for the already_vectorized
+ // hint. If the loop already has a loop id then copy the existing operands.
+ SmallVector<Value*, 4> Vals(1);
+ if (LoopID)
+ for (unsigned i = 1, ie = LoopID->getNumOperands(); i < ie; ++i)
+ Vals.push_back(LoopID->getOperand(i));
+
+ Twine Name = Prefix() + "width";
+ Vals.push_back(createHint(Context, Name.str(), Width));
+
+ MDNode *NewLoopID = MDNode::get(Context, Vals);
+ // Set operand 0 to refer to the loop id itself.
+ NewLoopID->replaceOperandWith(0, NewLoopID);
+
+ L->setLoopID(NewLoopID);
+ if (LoopID)
+ LoopID->replaceAllUsesWith(NewLoopID);
+
+ LoopID = NewLoopID;
+ }
+
+private:
+ MDNode *LoopID;
+
+ /// Find hints specified in the loop metadata.
+ void getHints(const Loop *L) {
+ if (!LoopID)
+ return;
+
+ // First operand should refer to the loop id itself.
+ assert(LoopID->getNumOperands() > 0 && "requires at least one operand");
+ assert(LoopID->getOperand(0) == LoopID && "invalid loop id");
+
+ for (unsigned i = 1, ie = LoopID->getNumOperands(); i < ie; ++i) {
+ const MDString *S = 0;
+ SmallVector<Value*, 4> Args;
+
+ // The expected hint is either a MDString or a MDNode with the first
+ // operand a MDString.
+ if (const MDNode *MD = dyn_cast<MDNode>(LoopID->getOperand(i))) {
+ if (!MD || MD->getNumOperands() == 0)
+ continue;
+ S = dyn_cast<MDString>(MD->getOperand(0));
+ for (unsigned i = 1, ie = MD->getNumOperands(); i < ie; ++i)
+ Args.push_back(MD->getOperand(i));
+ } else {
+ S = dyn_cast<MDString>(LoopID->getOperand(i));
+ assert(Args.size() == 0 && "too many arguments for MDString");
+ }
+
+ if (!S)
+ continue;
+
+ // Check if the hint starts with the vectorizer prefix.
+ StringRef Hint = S->getString();
+ if (!Hint.startswith(Prefix()))
+ continue;
+ // Remove the prefix.
+ Hint = Hint.substr(Prefix().size(), StringRef::npos);
+
+ if (Args.size() == 1)
+ getHint(Hint, Args[0]);
+ }
+ }
+
+ // Check string hint with one operand.
+ void getHint(StringRef Hint, Value *Arg) {
+ const ConstantInt *C = dyn_cast<ConstantInt>(Arg);
+ if (!C) return;
+ unsigned Val = C->getZExtValue();
+
+ if (Hint == "width") {
+ assert(isPowerOf2_32(Val) && Val <= MaxVectorWidth &&
+ "Invalid width metadata");
+ Width = Val;
+ } else if (Hint == "unroll") {
+ assert(isPowerOf2_32(Val) && Val <= MaxUnrollFactor &&
+ "Invalid unroll metadata");
+ Unroll = Val;
+ } else
+ DEBUG(dbgs() << "LV: ignoring unknown hint " << Hint);
+ }
+};
+
/// The LoopVectorize Pass.
struct LoopVectorize : public LoopPass {
/// Pass identification, replacement for typeid
DEBUG(dbgs() << "LV: Checking a loop in \"" <<
L->getHeader()->getParent()->getName() << "\"\n");
+ LoopVectorizeHints Hints(L);
+
+ if (Hints.Width == 1) {
+ DEBUG(dbgs() << "LV: Not vectorizing.\n");
+ return false;
+ }
+
// Check if it is legal to vectorize the loop.
LoopVectorizationLegality LVL(L, SE, DL, DT, TTI, AA, TLI);
if (!LVL.canVectorize()) {
// Select the optimal vectorization factor.
LoopVectorizationCostModel::VectorizationFactor VF;
- VF = CM.selectVectorizationFactor(OptForSize, VectorizationFactor);
+ VF = CM.selectVectorizationFactor(OptForSize, Hints.Width);
// Select the unroll factor.
- unsigned UF = CM.selectUnrollFactor(OptForSize, VectorizationUnroll,
- VF.Width, VF.Cost);
+ unsigned UF = CM.selectUnrollFactor(OptForSize, Hints.Unroll, VF.Width,
+ VF.Cost);
if (VF.Width == 1) {
DEBUG(dbgs() << "LV: Vectorization is possible but not beneficial.\n");
InnerLoopVectorizer LB(L, SE, LI, DT, DL, TLI, VF.Width, UF);
LB.vectorize(&LVL);
+ // Mark the loop as already vectorized to avoid vectorizing again.
+ Hints.setAlreadyVectorized(L);
+
DEBUG(verifyFunction(*L->getHeader()->getParent()));
return true;
}
BasicBlock *ExitBlock = OrigLoop->getExitBlock();
assert(ExitBlock && "Must have an exit block");
- // Mark the old scalar loop with metadata that tells us not to vectorize this
- // loop again if we run into it.
- MDNode *MD = MDNode::get(OldBasicBlock->getContext(), None);
- OldBasicBlock->getTerminator()->setMetadata(AlreadyVectorizedMDName, MD);
-
// Some loops have a single integer induction variable, while other loops
// don't. One example is c++ iterators that often have multiple pointer
// induction variables. In the code below we also support a case where we
Value *LoopVal = RdxPhi->getIncomingValueForBlock(Latch);
VectorParts &Val = getVectorValue(LoopVal);
for (unsigned part = 0; part < UF; ++part) {
- // Make sure to add the reduction stat value only to the
+ // Make sure to add the reduction stat value only to the
// first unroll part.
Value *StartVal = (part == 0) ? VectorStart : Identity;
cast<PHINode>(VecRdxPhi[part])->addIncoming(StartVal, VecPreheader);
}
bool LoopVectorizationLegality::canVectorize() {
- assert(TheLoop->getLoopPreheader() && "No preheader!!");
+ // We must have a loop in canonical form. Loops with indirectbr in them cannot
+ // be canonicalized.
+ if (!TheLoop->getLoopPreheader())
+ return false;
// We can only vectorize innermost loops.
if (TheLoop->getSubLoopsVector().size())
BasicBlock *PreHeader = TheLoop->getLoopPreheader();
BasicBlock *Header = TheLoop->getHeader();
- // If we marked the scalar loop as "already vectorized" then no need
- // to vectorize it again.
- if (Header->getTerminator()->getMetadata(AlreadyVectorizedMDName)) {
- DEBUG(dbgs() << "LV: This loop was vectorized before\n");
- return false;
- }
-
// Look for the attribute signaling the absence of NaNs.
Function &F = *Header->getParent();
if (F.hasFnAttribute("no-nans-fp-math"))
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