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.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@169950 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Transforms/IPO/PassManagerBuilder.cpp b/lib/Transforms/IPO/PassManagerBuilder.cpp
index a9a9f2e..0862786 100644
--- a/lib/Transforms/IPO/PassManagerBuilder.cpp
+++ b/lib/Transforms/IPO/PassManagerBuilder.cpp
@@ -189,7 +189,7 @@
MPM.add(createLoopDeletionPass()); // Delete dead loops
if (LoopVectorize && OptLevel > 1)
- MPM.add(createLoopVectorizePass());
+ MPM.add(createLoopVectorizePass(SizeLevel));
if (!DisableUnrollLoops)
MPM.add(createLoopUnrollPass()); // Unroll small loops
diff --git a/lib/Transforms/Vectorize/LoopVectorize.cpp b/lib/Transforms/Vectorize/LoopVectorize.cpp
index baa655c..d796716 100644
--- a/lib/Transforms/Vectorize/LoopVectorize.cpp
+++ b/lib/Transforms/Vectorize/LoopVectorize.cpp
@@ -51,9 +51,12 @@
/// 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 @@
}
// 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 @@
}
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_END(LoopVectorize, LV_NAME, lv_name, false, false)
namespace llvm {
- Pass *createLoopVectorizePass() {
- return new LoopVectorize();
+ Pass *createLoopVectorizePass(bool OptForSize = false) {
+ return new LoopVectorize(OptForSize);
}
}
diff --git a/lib/Transforms/Vectorize/LoopVectorize.h b/lib/Transforms/Vectorize/LoopVectorize.h
index 9d6d80e..e5a5259 100644
--- a/lib/Transforms/Vectorize/LoopVectorize.h
+++ b/lib/Transforms/Vectorize/LoopVectorize.h
@@ -420,10 +420,11 @@
const VectorTargetTransformInfo *Vtti):
TheLoop(Lp), SE(Se), Legal(Leg), VTTI(Vtti) { }
- /// Returns the most profitable vectorization factor for the loop that is
- /// smaller or equal to the VF argument. This method checks every power
- /// of two up to VF.
- unsigned findBestVectorizationFactor(unsigned VF = MaxVectorSize);
+ /// Returns the most profitable vectorization factor in powers of two.
+ /// This method checks every power of two up to VF. If UserVF is not ZERO
+ /// then this vectorization factor will be selected if vectorization is
+ /// possible.
+ unsigned selectVectorizationFactor(bool OptForSize, unsigned UserVF);
private:
/// Returns the expected execution cost. The unit of the cost does
diff --git a/lib/Transforms/Vectorize/Vectorize.cpp b/lib/Transforms/Vectorize/Vectorize.cpp
index 3fb36ca..cf7d4ee 100644
--- a/lib/Transforms/Vectorize/Vectorize.cpp
+++ b/lib/Transforms/Vectorize/Vectorize.cpp
@@ -1,4 +1,4 @@
-//===-- Vectorize.cpp -----------------------------------------------------===//
+ //===-- Vectorize.cpp -----------------------------------------------------===//
//
// The LLVM Compiler Infrastructure
//
@@ -39,5 +39,5 @@
}
void LLVMAddLoopVectorizePass(LLVMPassManagerRef PM) {
- unwrap(PM)->add(createLoopVectorizePass());
+ unwrap(PM)->add(createLoopVectorizePass(0));
}