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LoopVectorizer: When -Os is used, vectorize only loops that dont require a tail loop. There is no testcase because I dont know of a way to initialize the loop vectorizer pass without adding an additional hidden flag.

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@169950 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Nadav Rotem
2012-12-12 01:11:46 +00:00
parent 61f4dfe369
commit 5da804150d
6 changed files with 69 additions and 30 deletions
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80
lib/Transforms/Vectorize/LoopVectorize.cpp
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@ -51,9 +51,12 @@ namespace {
/// The LoopVectorize Pass.
struct LoopVectorize : public LoopPass {
static char ID; // Pass identification, replacement for typeid
/// Pass identification, replacement for typeid
static char ID;
/// Optimize for size. Do not generate tail loops.
bool OptForSize;
LoopVectorize() : LoopPass(ID) {
explicit LoopVectorize(bool OptSz = false) : LoopPass(ID), OptForSize(OptSz) {
initializeLoopVectorizePass(*PassRegistry::getPassRegistry());
}
@ -85,23 +88,17 @@ struct LoopVectorize : public LoopPass {
}
// Select the preffered vectorization factor.
unsigned VF = 1;
if (VectorizationFactor == 0) {
const VectorTargetTransformInfo *VTTI = 0;
if (TTI)
VTTI = TTI->getVectorTargetTransformInfo();
// Use the cost model.
LoopVectorizationCostModel CM(L, SE, &LVL, VTTI);
VF = CM.findBestVectorizationFactor();
const VectorTargetTransformInfo *VTTI = 0;
if (TTI)
VTTI = TTI->getVectorTargetTransformInfo();
// Use the cost model.
LoopVectorizationCostModel CM(L, SE, &LVL, VTTI);
unsigned VF = CM.selectVectorizationFactor(OptForSize,
VectorizationFactor);
if (VF == 1) {
DEBUG(dbgs() << "LV: Vectorization is possible but not beneficial.\n");
return false;
}
} else {
// Use the user command flag.
VF = VectorizationFactor;
if (VF == 1) {
DEBUG(dbgs() << "LV: Vectorization is possible but not beneficial.\n");
return false;
}
DEBUG(dbgs() << "LV: Found a vectorizable loop ("<< VF << ") in "<<
@ -1886,7 +1883,48 @@ bool LoopVectorizationLegality::hasComputableBounds(Value *Ptr) {
}
unsigned
LoopVectorizationCostModel::findBestVectorizationFactor(unsigned VF) {
LoopVectorizationCostModel::selectVectorizationFactor(bool OptForSize,
unsigned UserVF) {
if (OptForSize && Legal->getRuntimePointerCheck()->Need) {
DEBUG(dbgs() << "LV: Aborting. Runtime ptr check is required in Os.\n");
return 1;
}
// Find the trip count.
unsigned TC = SE->getSmallConstantTripCount(TheLoop, TheLoop->getLoopLatch());
DEBUG(dbgs() << "LV: Found trip count:"<<TC<<"\n");
unsigned VF = MaxVectorSize;
// If we optimize the program for size, avoid creating the tail loop.
if (OptForSize) {
// If we are unable to calculate the trip count then don't try to vectorize.
if (TC < 2) {
DEBUG(dbgs() << "LV: Aborting. A tail loop is required in Os.\n");
return 1;
}
// Find the maximum SIMD width that can fit within the trip count.
VF = TC % MaxVectorSize;
if (VF == 0)
VF = MaxVectorSize;
// If the trip count that we found modulo the vectorization factor is not
// zero then we require a tail.
if (VF < 2) {
DEBUG(dbgs() << "LV: Aborting. A tail loop is required in Os.\n");
return 1;
}
}
if (UserVF != 0) {
assert(isPowerOf2_32(UserVF) && "VF needs to be a power of two");
DEBUG(dbgs() << "LV: Using user VF "<<UserVF<<".\n");
return UserVF;
}
if (!VTTI) {
DEBUG(dbgs() << "LV: No vector target information. Not vectorizing. \n");
return 1;
@ -2121,8 +2159,8 @@ INITIALIZE_PASS_DEPENDENCY(LoopSimplify)
INITIALIZE_PASS_END(LoopVectorize, LV_NAME, lv_name, false, false)
namespace llvm {
Pass *createLoopVectorizePass() {
return new LoopVectorize();
Pass *createLoopVectorizePass(bool OptForSize = false) {
return new LoopVectorize(OptForSize);
}
}