From 22920b59864cac3b62d158fd4111cfda3c09c67a Mon Sep 17 00:00:00 2001
From: Chris Lattner <sabre@nondot.org>
Date: Sun, 26 Dec 2010 20:45:45 +0000
Subject: [PATCH] sketch more of this out.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@122567 91177308-0d34-0410-b5e6-96231b3b80d8
---
lib/Transforms/Scalar/LoopIdiomRecognize.cpp | 84 +++++++++++++++-----
1 file changed, 64 insertions(+), 20 deletions(-)
diff --git a/lib/Transforms/Scalar/LoopIdiomRecognize.cpp b/lib/Transforms/Scalar/LoopIdiomRecognize.cpp
index 270c4afcc1d..eb7d4930edf 100644
--- a/lib/Transforms/Scalar/LoopIdiomRecognize.cpp
+++ b/lib/Transforms/Scalar/LoopIdiomRecognize.cpp
@@ -17,6 +17,8 @@
#include "llvm/Transforms/Scalar.h"
#include "llvm/Analysis/LoopPass.h"
#include "llvm/Analysis/ScalarEvolutionExpressions.h"
+#include "llvm/Analysis/ValueTracking.h"
+#include "llvm/Target/TargetData.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
using namespace llvm;
@@ -26,6 +28,9 @@ using namespace llvm;
namespace {
class LoopIdiomRecognize : public LoopPass {
+ Loop *CurLoop;
+ const TargetData *TD;
+ ScalarEvolution *SE;
public:
static char ID;
explicit LoopIdiomRecognize() : LoopPass(ID) {
@@ -34,7 +39,7 @@ namespace {
bool runOnLoop(Loop *L, LPPassManager &LPM);
- bool scanBlock(BasicBlock *BB, Loop *L);
+ bool processLoopStore(StoreInst *SI, const SCEV *BECount);
/// This transformation requires natural loop information & requires that
/// loop preheaders be inserted into the CFG.
@@ -66,38 +71,77 @@ INITIALIZE_PASS_END(LoopIdiomRecognize, "loop-idiom", "Recognize loop idioms",
Pass *llvm::createLoopIdiomPass() { return new LoopIdiomRecognize(); }
bool LoopIdiomRecognize::runOnLoop(Loop *L, LPPassManager &LPM) {
+ CurLoop = L;
+
// We only look at trivial single basic block loops.
// TODO: eventually support more complex loops, scanning the header.
if (L->getBlocks().size() != 1)
return false;
+ // The trip count of the loop must be analyzable.
+ SE = &getAnalysis<ScalarEvolution>();
+ if (!SE->hasLoopInvariantBackedgeTakenCount(L))
+ return false;
+ const SCEV *BECount = SE->getBackedgeTakenCount(L);
+ if (isa<SCEVCouldNotCompute>(BECount)) return false;
+
+ // We require target data for now.
+ TD = getAnalysisIfAvailable<TargetData>();
+ if (TD == 0) return false;
+
BasicBlock *BB = L->getHeader();
- DEBUG(dbgs() << "Loop Idiom Recognize: F[" << BB->getParent()->getName()
+ DEBUG(dbgs() << "loop-idiom Scanning: F[" << BB->getParent()->getName()
<< "] Loop %" << BB->getName() << "\n");
- return scanBlock(BB, L);
+ bool MadeChange = false;
+ for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ) {
+ // Look for store instructions, which may be memsets.
+ if (StoreInst *SI = dyn_cast<StoreInst>(I++))
+ MadeChange |= processLoopStore(SI, BECount);
+ }
+
+ return MadeChange;
}
/// scanBlock - Look over a block to see if we can promote anything out of it.
-bool LoopIdiomRecognize::scanBlock(BasicBlock *BB, Loop *L) {
- ScalarEvolution &SE = getAnalysis<ScalarEvolution>();
+bool LoopIdiomRecognize::processLoopStore(StoreInst *SI, const SCEV *BECount) {
+ Value *StoredVal = SI->getValueOperand();
- for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ) {
- // Look for store instructions, which may be memsets.
- StoreInst *SI = dyn_cast<StoreInst>(I++);
- if (SI == 0) continue;
-
- // See if the pointer expression is an AddRec like {base,+,1} on the current
- // loop, which indicates a strided store. If we have something else, it's a
- // random store we can't handle.
- const SCEVAddRecExpr *Ev =
- dyn_cast<SCEVAddRecExpr>(SE.getSCEV(SI->getPointerOperand()));
- if (Ev == 0 || Ev->getLoop() != L)
- continue;
-
- errs() << "Found strided store: " << *Ev << "\n";
- }
+ // Check to see if the store updates all bits in memory. We don't want to
+ // process things like a store of i3. We also require that the store be a
+ // multiple of a byte.
+ uint64_t SizeInBits = TD->getTypeSizeInBits(StoredVal->getType());
+ if ((SizeInBits & 7) || (SizeInBits >> 32) != 0 ||
+ SizeInBits != TD->getTypeStoreSizeInBits(StoredVal->getType()))
+ return false;
+ // See if the pointer expression is an AddRec like {base,+,1} on the current
+ // loop, which indicates a strided store. If we have something else, it's a
+ // random store we can't handle.
+ const SCEVAddRecExpr *Ev =
+ dyn_cast<SCEVAddRecExpr>(SE->getSCEV(SI->getPointerOperand()));
+ if (Ev == 0 || Ev->getLoop() != CurLoop || !Ev->isAffine())
+ return false;
+
+ // Check to see if the stride matches the size of the store. If so, then we
+ // know that every byte is touched in the loop.
+ unsigned StoreSize = (unsigned)SizeInBits >> 3;
+ const SCEVConstant *Stride = dyn_cast<SCEVConstant>(Ev->getOperand(1));
+ if (Stride == 0 || StoreSize != Stride->getValue()->getValue())
+ return false;
+
+ errs() << "Found strided store: " << *Ev << "\n";
+
+ // Check for memcpy here.
+
+
+ // If the stored value is a byte-wise value (like i32 -1), then it may be
+ // turned into a memset of i8 -1, assuming that all the consequtive bytes
+ // are stored. A store of i32 0x01020304 can never be turned into a memset.
+ Value *SplatValue = isBytewiseValue(StoredVal);
+ if (SplatValue == 0) return false;
+
+
return false;
}