summaryrefslogtreecommitdiffstats
path: root/llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp
diff options
context:
space:
mode:
Diffstat (limited to 'llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp')
-rw-r--r--llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp103
1 files changed, 3 insertions, 100 deletions
diff --git a/llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp b/llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp
index 371fd398e35..1ec38e56aa4 100644
--- a/llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp
+++ b/llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp
@@ -34,7 +34,6 @@
#include "llvm/IR/GlobalVariable.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/IntrinsicInst.h"
-#include "llvm/IR/LLVMContext.h"
#include "llvm/Pass.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
@@ -50,18 +49,12 @@ STATISTIC(NumRedundantStores, "Number of redundant stores deleted");
STATISTIC(NumFastStores, "Number of stores deleted");
STATISTIC(NumFastOther , "Number of other instrs removed");
STATISTIC(NumCompletePartials, "Number of stores dead by later partials");
-STATISTIC(NumModifiedStores, "Number of stores modified");
static cl::opt<bool>
EnablePartialOverwriteTracking("enable-dse-partial-overwrite-tracking",
cl::init(true), cl::Hidden,
cl::desc("Enable partial-overwrite tracking in DSE"));
-static cl::opt<bool>
-EnablePartialStoreMerging("enable-dse-partial-store-merging",
- cl::init(true), cl::Hidden,
- cl::desc("Enable partial store merging in DSE"));
-
//===----------------------------------------------------------------------===//
// Helper functions
@@ -294,22 +287,14 @@ static uint64_t getPointerSize(const Value *V, const DataLayout &DL,
}
namespace {
-enum OverwriteResult {
- OW_Begin,
- OW_Complete,
- OW_End,
- OW_PartialEarlierWithFullLater,
- OW_Unknown
-};
+enum OverwriteResult { OW_Begin, OW_Complete, OW_End, OW_Unknown };
}
/// Return 'OW_Complete' if a store to the 'Later' location completely
/// overwrites a store to the 'Earlier' location, 'OW_End' if the end of the
/// 'Earlier' location is completely overwritten by 'Later', 'OW_Begin' if the
-/// beginning of the 'Earlier' location is overwritten by 'Later'.
-/// 'OW_PartialEarlierWithFullLater' means that an earlier (big) store was
-/// overwritten by a latter (smaller) store which doesn't write outside the big
-/// store's memory locations. Returns 'OW_Unknown' if nothing can be determined.
+/// beginning of the 'Earlier' location is overwritten by 'Later', or
+/// 'OW_Unknown' if nothing can be determined.
static OverwriteResult isOverwrite(const MemoryLocation &Later,
const MemoryLocation &Earlier,
const DataLayout &DL,
@@ -442,19 +427,6 @@ static OverwriteResult isOverwrite(const MemoryLocation &Later,
}
}
- // Check for an earlier store which writes to all the memory locations that
- // the later store writes to.
- if (EnablePartialStoreMerging && LaterOff >= EarlierOff &&
- int64_t(EarlierOff + Earlier.Size) > LaterOff &&
- uint64_t(LaterOff - EarlierOff) + Later.Size <= Earlier.Size) {
- DEBUG(dbgs() << "DSE: Partial overwrite an earlier load [" << EarlierOff
- << ", " << int64_t(EarlierOff + Earlier.Size)
- << ") by a later store [" << LaterOff << ", "
- << int64_t(LaterOff + Later.Size) << ")\n");
- // TODO: Maybe come up with a better name?
- return OW_PartialEarlierWithFullLater;
- }
-
// Another interesting case is if the later store overwrites the end of the
// earlier store.
//
@@ -1122,8 +1094,6 @@ static bool eliminateDeadStores(BasicBlock &BB, AliasAnalysis *AA,
// If we find a write that is a) removable (i.e., non-volatile), b) is
// completely obliterated by the store to 'Loc', and c) which we know that
// 'Inst' doesn't load from, then we can remove it.
- // Also try to merge two stores if a latter one only touches memory
- // written to by the earlier one.
if (isRemovable(DepWrite) &&
!isPossibleSelfRead(Inst, Loc, DepWrite, *TLI, *AA)) {
int64_t InstWriteOffset, DepWriteOffset;
@@ -1153,73 +1123,6 @@ static bool eliminateDeadStores(BasicBlock &BB, AliasAnalysis *AA,
bool IsOverwriteEnd = (OR == OW_End);
MadeChange |= tryToShorten(DepWrite, DepWriteOffset, EarlierSize,
InstWriteOffset, LaterSize, IsOverwriteEnd);
- } else if (EnablePartialStoreMerging &&
- OR == OW_PartialEarlierWithFullLater) {
- auto *Earlier = dyn_cast<StoreInst>(DepWrite);
- auto *Later = dyn_cast<StoreInst>(Inst);
- if (Earlier && isa<ConstantInt>(Earlier->getValueOperand()) &&
- Later && isa<ConstantInt>(Later->getValueOperand())) {
- // If the store we find is:
- // a) partially overwritten by the store to 'Loc'
- // b) the latter store is fully contained in the earlier one and
- // c) They both have a contant value
- // Merge the two stores, replacing the earlier store's value with a
- // merge of both values.
- // TODO: Deal with other constant types (vectors, etc), and probably
- // some mem intrinsics (if needed)
-
- APInt EarlierValue =
- cast<ConstantInt>(Earlier->getValueOperand())->getValue();
- APInt LaterValue =
- cast<ConstantInt>(Later->getValueOperand())->getValue();
- unsigned LaterBits = LaterValue.getBitWidth();
- assert(EarlierValue.getBitWidth() > LaterValue.getBitWidth());
- LaterValue = LaterValue.zext(EarlierValue.getBitWidth());
-
- // Offset of the smaller store inside the larger store
- unsigned BitOffsetDiff = (InstWriteOffset - DepWriteOffset) * 8;
- unsigned LShiftAmount =
- DL.isBigEndian()
- ? EarlierValue.getBitWidth() - BitOffsetDiff - LaterBits
- : BitOffsetDiff;
- APInt Mask =
- APInt::getBitsSet(EarlierValue.getBitWidth(), LShiftAmount,
- LShiftAmount + LaterBits);
- // Clear the bits we'll be replacing, then OR with the smaller
- // store, shifted appropriately.
- APInt Merged =
- (EarlierValue & ~Mask) | (LaterValue << LShiftAmount);
- DEBUG(dbgs() << "DSE: Merge Stores:\n Earlier: " << *DepWrite
- << "\n Later: " << *Inst
- << "\n Merged Value: " << Merged << '\n');
-
- auto *SI = new StoreInst(
- ConstantInt::get(Earlier->getValueOperand()->getType(), Merged),
- Earlier->getPointerOperand(), false, Earlier->getAlignment(),
- Earlier->getOrdering(), Earlier->getSyncScopeID(), DepWrite);
-
- unsigned MDToKeep[] = {LLVMContext::MD_dbg, LLVMContext::MD_tbaa,
- LLVMContext::MD_alias_scope,
- LLVMContext::MD_noalias,
- LLVMContext::MD_nontemporal};
- SI->copyMetadata(*DepWrite, MDToKeep);
- ++NumModifiedStores;
-
- // Remove earlier, wider, store
- size_t Idx = InstrOrdering.lookup(DepWrite);
- InstrOrdering.erase(DepWrite);
- InstrOrdering.insert(std::make_pair(SI, Idx));
-
- // Delete the old stores and now-dead instructions that feed them.
- deleteDeadInstruction(Inst, &BBI, *MD, *TLI, IOL, &InstrOrdering);
- deleteDeadInstruction(DepWrite, &BBI, *MD, *TLI, IOL,
- &InstrOrdering);
- MadeChange = true;
-
- //// We erased DepWrite; start over.
- InstDep = MD->getDependency(SI);
- continue;
- }
}
}
OpenPOWER on IntegriCloud