[DSE]Enhance shorthening MemIntrinsic based on OverlapIntervals

Summary:
This change use the overlap interval map built from partial overwrite tracking to perform shortening MemIntrinsics.
Add test cases which was missing opportunities before.

Reviewers: hfinkel, eeckstein, mcrosier

Subscribers: mcrosier, llvm-commits

Differential Revision: https://reviews.llvm.org/D21909

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@275571 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Transforms/Scalar/DeadStoreElimination.cpp

@@ -290,8 +290,8 @@ enum OverwriteResult {
 };
 }
 
-typedef DenseMap<Instruction *,
-                 std::map<int64_t, int64_t>> InstOverlapIntervalsTy;
+typedef std::map<int64_t, int64_t> OverlapIntervalsTy;
+typedef DenseMap<Instruction *, OverlapIntervalsTy> InstOverlapIntervalsTy;
 
 /// Return 'OverwriteComplete' if a store to the 'Later' location completely
 /// overwrites a store to the 'Earlier' location, 'OverwriteEnd' if the end of
@@ -438,9 +438,9 @@ static OverwriteResult isOverwrite(const MemoryLocation &Later,
   //
   // In this case we may want to trim the size of earlier to avoid generating
   // writes to addresses which will definitely be overwritten later
-  if (LaterOff > EarlierOff &&
-      LaterOff < int64_t(EarlierOff + Earlier.Size) &&
-      int64_t(LaterOff + Later.Size) >= int64_t(EarlierOff + Earlier.Size))
+  if (!EnablePartialOverwriteTracking &&
+      (LaterOff > EarlierOff && LaterOff < int64_t(EarlierOff + Earlier.Size) &&
+       int64_t(LaterOff + Later.Size) >= int64_t(EarlierOff + Earlier.Size)))
     return OverwriteEnd;
 
   // Finally, we also need to check if the later store overwrites the beginning
@@ -452,9 +452,11 @@ static OverwriteResult isOverwrite(const MemoryLocation &Later,
   // In this case we may want to move the destination address and trim the size
   // of earlier to avoid generating writes to addresses which will definitely
   // be overwritten later.
-  if (LaterOff <= EarlierOff && int64_t(LaterOff + Later.Size) > EarlierOff) {
-    assert (int64_t(LaterOff + Later.Size) < int64_t(EarlierOff + Earlier.Size)
-            && "Expect to be handled as OverwriteComplete" );
+  if (!EnablePartialOverwriteTracking &&
+      (LaterOff <= EarlierOff && int64_t(LaterOff + Later.Size) > EarlierOff)) {
+    assert(int64_t(LaterOff + Later.Size) <
+               int64_t(EarlierOff + Earlier.Size) &&
+           "Expect to be handled as OverwriteComplete");
     return OverwriteBegin;
   }
   // Otherwise, they don't completely overlap.
@@ -819,6 +821,119 @@ static bool handleEndBlock(BasicBlock &BB, AliasAnalysis *AA,
   return MadeChange;
 }
 
+static bool tryToShorten(Instruction *EarlierWrite, int64_t &EarlierOffset,
+                         int64_t &EarlierSize, int64_t LaterOffset,
+                         int64_t LaterSize, bool IsOverwriteEnd) {
+  // TODO: base this on the target vector size so that if the earlier
+  // store was too small to get vector writes anyway then its likely
+  // a good idea to shorten it
+  // Power of 2 vector writes are probably always a bad idea to optimize
+  // as any store/memset/memcpy is likely using vector instructions so
+  // shortening it to not vector size is likely to be slower
+  MemIntrinsic *EarlierIntrinsic = cast<MemIntrinsic>(EarlierWrite);
+  unsigned EarlierWriteAlign = EarlierIntrinsic->getAlignment();
+  if (!IsOverwriteEnd)
+    LaterOffset = int64_t(LaterOffset + LaterSize);
+
+  if (!(llvm::isPowerOf2_64(LaterOffset) && EarlierWriteAlign <= LaterOffset) &&
+      !((EarlierWriteAlign != 0) && LaterOffset % EarlierWriteAlign == 0))
+    return false;
+
+  DEBUG(dbgs() << "DSE: Remove Dead Store:\n  OW "
+               << (IsOverwriteEnd ? "END" : "BEGIN") << ": " << *EarlierWrite
+               << "\n  KILLER (offset " << LaterOffset << ", " << EarlierSize
+               << ")\n");
+
+  int64_t NewLength = IsOverwriteEnd
+                          ? LaterOffset - EarlierOffset
+                          : EarlierSize - (LaterOffset - EarlierOffset);
+
+  Value *EarlierWriteLength = EarlierIntrinsic->getLength();
+  Value *TrimmedLength =
+      ConstantInt::get(EarlierWriteLength->getType(), NewLength);
+  EarlierIntrinsic->setLength(TrimmedLength);
+
+  EarlierSize = NewLength;
+  if (!IsOverwriteEnd) {
+    int64_t OffsetMoved = (LaterOffset - EarlierOffset);
+    Value *Indices[1] = {
+        ConstantInt::get(EarlierWriteLength->getType(), OffsetMoved)};
+    GetElementPtrInst *NewDestGEP = GetElementPtrInst::CreateInBounds(
+        EarlierIntrinsic->getRawDest(), Indices, "", EarlierWrite);
+    EarlierIntrinsic->setDest(NewDestGEP);
+    EarlierOffset = EarlierOffset + OffsetMoved;
+  }
+  return true;
+}
+
+static bool tryToShortenEnd(Instruction *EarlierWrite,
+                            OverlapIntervalsTy &IntervalMap,
+                            int64_t &EarlierStart, int64_t &EarlierSize) {
+  if (IntervalMap.empty() || !isShortenableAtTheEnd(EarlierWrite))
+    return false;
+
+  OverlapIntervalsTy::iterator OII = --IntervalMap.end();
+  int64_t LaterStart = OII->second;
+  int64_t LaterSize = OII->first - LaterStart;
+
+  if (LaterStart > EarlierStart && LaterStart < EarlierStart + EarlierSize &&
+      LaterStart + LaterSize >= EarlierStart + EarlierSize) {
+    if (tryToShorten(EarlierWrite, EarlierStart, EarlierSize, LaterStart,
+                     LaterSize, true)) {
+      IntervalMap.erase(OII);
+      return true;
+    }
+  }
+  return false;
+}
+
+static bool tryToShortenBegin(Instruction *EarlierWrite,
+                              OverlapIntervalsTy &IntervalMap,
+                              int64_t &EarlierStart, int64_t &EarlierSize) {
+  if (IntervalMap.empty() || !isShortenableAtTheBeginning(EarlierWrite))
+    return false;
+
+  OverlapIntervalsTy::iterator OII = IntervalMap.begin();
+  int64_t LaterStart = OII->second;
+  int64_t LaterSize = OII->first - LaterStart;
+
+  if (LaterStart <= EarlierStart && LaterStart + LaterSize > EarlierStart) {
+    assert(LaterStart + LaterSize < EarlierStart + EarlierSize &&
+           "Should have been handled as OverwriteComplete");
+    if (tryToShorten(EarlierWrite, EarlierStart, EarlierSize, LaterStart,
+                     LaterSize, false)) {
+      IntervalMap.erase(OII);
+      return true;
+    }
+  }
+  return false;
+}
+
+static bool removePartiallyOverlappedStores(AliasAnalysis *AA,
+                                            const DataLayout &DL,
+                                            InstOverlapIntervalsTy &IOL) {
+  bool Changed = false;
+  for (auto OI : IOL) {
+    Instruction *EarlierWrite = OI.first;
+    MemoryLocation Loc = getLocForWrite(EarlierWrite, *AA);
+    assert(isRemovable(EarlierWrite) && "Expect only removable instruction");
+    assert(Loc.Size != MemoryLocation::UnknownSize && "Unexpected mem loc");
+
+    const Value *Ptr = Loc.Ptr->stripPointerCasts();
+    int64_t EarlierStart = 0;
+    int64_t EarlierSize = int64_t(Loc.Size);
+    GetPointerBaseWithConstantOffset(Ptr, EarlierStart, DL);
+    OverlapIntervalsTy &IntervalMap = OI.second;
+    Changed =
+        tryToShortenEnd(EarlierWrite, IntervalMap, EarlierStart, EarlierSize);
+    if (IntervalMap.empty())
+      continue;
+    Changed |=
+        tryToShortenBegin(EarlierWrite, IntervalMap, EarlierStart, EarlierSize);
+  }
+  return Changed;
+}
+
 static bool eliminateNoopStore(Instruction *Inst, BasicBlock::iterator &BBI,
                                AliasAnalysis *AA, MemoryDependenceResults *MD,
                                const DataLayout &DL,
@@ -936,7 +1051,7 @@ static bool eliminateDeadStores(BasicBlock &BB, AliasAnalysis *AA,
         if (OR == OverwriteComplete) {
           DEBUG(dbgs() << "DSE: Remove Dead Store:\n  DEAD: "
                 << *DepWrite << "\n  KILLER: " << *Inst << '\n');
-
+          IOL.erase(DepWrite);
           // Delete the store and now-dead instructions that feed it.
           deleteDeadInstruction(DepWrite, &BBI, *MD, *TLI);
           ++NumFastStores;
@@ -948,48 +1063,14 @@ static bool eliminateDeadStores(BasicBlock &BB, AliasAnalysis *AA,
         } else if ((OR == OverwriteEnd && isShortenableAtTheEnd(DepWrite)) ||
                    ((OR == OverwriteBegin &&
                      isShortenableAtTheBeginning(DepWrite)))) {
-          // TODO: base this on the target vector size so that if the earlier
-          // store was too small to get vector writes anyway then its likely
-          // a good idea to shorten it
-          // Power of 2 vector writes are probably always a bad idea to optimize
-          // as any store/memset/memcpy is likely using vector instructions so
-          // shortening it to not vector size is likely to be slower
-          MemIntrinsic *DepIntrinsic = cast<MemIntrinsic>(DepWrite);
-          unsigned DepWriteAlign = DepIntrinsic->getAlignment();
+          assert(!EnablePartialOverwriteTracking && "Do not expect to perform "
+                                                    "when partial-overwrite "
+                                                    "tracking is enabled");
+          int64_t EarlierSize = DepLoc.Size;
+          int64_t LaterSize = Loc.Size;
           bool IsOverwriteEnd = (OR == OverwriteEnd);
-          if (!IsOverwriteEnd)
-            InstWriteOffset = int64_t(InstWriteOffset + Loc.Size);
-
-          if ((llvm::isPowerOf2_64(InstWriteOffset) &&
-               DepWriteAlign <= InstWriteOffset) ||
-              ((DepWriteAlign != 0) && InstWriteOffset % DepWriteAlign == 0)) {
-
-            DEBUG(dbgs() << "DSE: Remove Dead Store:\n  OW "
-                         << (IsOverwriteEnd ? "END" : "BEGIN") << ": "
-                         << *DepWrite << "\n  KILLER (offset "
-                         << InstWriteOffset << ", " << DepLoc.Size << ")"
-                         << *Inst << '\n');
-
-            int64_t NewLength =
-                IsOverwriteEnd
-                    ? InstWriteOffset - DepWriteOffset
-                    : DepLoc.Size - (InstWriteOffset - DepWriteOffset);
-
-            Value *DepWriteLength = DepIntrinsic->getLength();
-            Value *TrimmedLength =
-                ConstantInt::get(DepWriteLength->getType(), NewLength);
-            DepIntrinsic->setLength(TrimmedLength);
-
-            if (!IsOverwriteEnd) {
-              int64_t OffsetMoved = (InstWriteOffset - DepWriteOffset);
-              Value *Indices[1] = {
-                  ConstantInt::get(DepWriteLength->getType(), OffsetMoved)};
-              GetElementPtrInst *NewDestGEP = GetElementPtrInst::CreateInBounds(
-                  DepIntrinsic->getRawDest(), Indices, "", DepWrite);
-              DepIntrinsic->setDest(NewDestGEP);
-            }
-            MadeChange = true;
-          }
+          MadeChange = tryToShorten(DepWrite, DepWriteOffset, EarlierSize,
+                                    InstWriteOffset, LaterSize, IsOverwriteEnd);
         }
       }
 
@@ -1012,6 +1093,9 @@ static bool eliminateDeadStores(BasicBlock &BB, AliasAnalysis *AA,
     }
   }
 
+  if (EnablePartialOverwriteTracking)
+    MadeChange |= removePartiallyOverlappedStores(AA, DL, IOL);
+
   // If this block ends in a return, unwind, or unreachable, all allocas are
   // dead at its end, which means stores to them are also dead.
   if (BB.getTerminator()->getNumSuccessors() == 0)

test/Transforms/DeadStoreElimination/OverwriteStoreBegin.ll

@@ -86,5 +86,23 @@ entry:
   ret void
 }
 
+define void @write8To15AndThen0To7(i64* nocapture %P) {
+entry:
+; CHECK-LABEL: @write8To15AndThen0To7(
+; CHECK: [[GEP:%[0-9]+]] = getelementptr inbounds i8, i8* %mybase0, i64 16
+; CHECK: tail call void @llvm.memset.p0i8.i64(i8* [[GEP]], i8 0, i64 16, i32 8, i1 false)
+
+  %base0 = bitcast i64* %P to i8*
+  %mybase0 = getelementptr inbounds i8, i8* %base0, i64 0
+  tail call void @llvm.memset.p0i8.i64(i8* %mybase0, i8 0, i64 32, i32 8, i1 false)
+
+  %base64_0 = getelementptr inbounds i64, i64* %P, i64 0
+  %base64_1 = getelementptr inbounds i64, i64* %P, i64 1
+
+  store i64 1, i64* %base64_1
+  store i64 2, i64* %base64_0
+  ret void
+}
+
 declare void @llvm.memset.p0i8.i64(i8* nocapture, i8, i64, i32, i1) nounwind
 

test/Transforms/DeadStoreElimination/OverwriteStoreEnd.ll

@@ -93,3 +93,20 @@ entry:
   store i64 3, i64* %tf_trapno, align 8
   ret void
 }
+
+define void @write16To23AndThen24To31(i64* nocapture %P, i64 %n64, i32 %n32, i16 %n16, i8 %n8) {
+entry:
+; CHECK-LABEL: @write16To23AndThen24To31(
+; CHECK: tail call void @llvm.memset.p0i8.i64(i8* %mybase0, i8 0, i64 16, i32 8, i1 false)
+
+  %base0 = bitcast i64* %P to i8*
+  %mybase0 = getelementptr inbounds i8, i8* %base0, i64 0
+  tail call void @llvm.memset.p0i8.i64(i8* %mybase0, i8 0, i64 32, i32 8, i1 false)
+
+  %base64_2 = getelementptr inbounds i64, i64* %P, i64 2
+  %base64_3 = getelementptr inbounds i64, i64* %P, i64 3
+
+  store i64 3, i64* %base64_2
+  store i64 3, i64* %base64_3
+  ret void
+}