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Add support for llvm.vectorizer metadata

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- llvm.loop.parallel metadata has been renamed to llvm.loop to be more generic
  by making the root of additional loop metadata.
  - Loop::isAnnotatedParallel now looks for llvm.loop and associated
    llvm.mem.parallel_loop_access
  - document llvm.loop and update llvm.mem.parallel_loop_access
- add support for llvm.vectorizer.width and llvm.vectorizer.unroll
  - document llvm.vectorizer.* metadata
  - add utility class LoopVectorizerHints for getting/setting loop metadata
  - use llvm.vectorizer.width=1 to indicate already vectorized instead of
    already_vectorized
- update existing tests that used llvm.loop.parallel and
  llvm.vectorizer.already_vectorized

Reviewed by: Nadav Rotem


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@182802 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Paul Redmond
2013-05-28 20:00:34 +00:00
parent a32edcfbc5
commit ee21b6f7b4
10 changed files with 381 additions and 88 deletions
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lib/Transforms/Vectorize/LoopVectorize.cpp
+139 -20
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@@ -119,11 +119,11 @@ static const unsigned TinyTripCountUnrollThreshold = 128;
/// 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 {
@@ -768,6 +768,127 @@ private:
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
@@ -806,6 +927,13 @@ struct LoopVectorize : public LoopPass {
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()) {
@@ -833,10 +961,10 @@ struct LoopVectorize : public LoopPass {
// 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");
@@ -851,6 +979,9 @@ struct LoopVectorize : public LoopPass {
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;
}
@@ -1318,11 +1449,6 @@ InnerLoopVectorizer::createEmptyLoop(LoopVectorizationLegality *Legal) {
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
@@ -2516,13 +2642,6 @@ bool LoopVectorizationLegality::canVectorizeInstrs() {
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"))