Move isPointerOffset function to ValueTracking.

[eugenis]

Summary

To be reused in MemTag sanitizer.

[vitalybuka]

It's does not change code, but looks like it can be improved in followup patches

llvm/lib/Analysis/ValueTracking.cpp

5705

pair<int64_t, bool>

5718

This line is confusing:

return VariableIdxFound = true;

5737

pair<bool, int64_t> llvm::isPointerOffset(const Value *Ptr1, const Value *Ptr2,

[eugenis]

I'll submit this as is and then refactor in a follow up.
Thanks!

llvm/lib/Analysis/ValueTracking.cpp

5705

Even better, Optional<int64_t>

llvm/include/llvm/Analysis/ValueTracking.h

Optional<bool> isImpliedCondition(const Value *LHS, const Value *RHS,
                                     const DataLayout &DL, bool LHSIsTrue = true,
                                     unsigned Depth = 0);
 
   /// Return the boolean condition value in the context of the given instruction
   /// if it is known based on dominating conditions.
   Optional<bool> isImpliedByDomCondition(const Value *Cond,
                                          const Instruction *ContextI,
                                          const DataLayout &DL);
+
+  /// Return true if Ptr1 is provably equal to Ptr2 plus a constant offset, and
+  /// return that constant offset. For example, Ptr1 might be &A[42], and Ptr2
+  /// might be &A[40]. In this case offset would be -8.
+  bool isPointerOffset(Value *Ptr1, Value *Ptr2, int64_t &Offset,
+                       const DataLayout &DL);
 } // end namespace llvm
 
 #endif // LLVM_ANALYSIS_VALUETRACKING_H

llvm/lib/Analysis/ValueTracking.cpp

ConstantRange llvm::computeConstantRange(const Value *V, bool UseInstrInfo) {
   ConstantRange CR = ConstantRange::getNonEmpty(Lower, Upper);
 
   if (auto *I = dyn_cast<Instruction>(V))
     if (auto *Range = IIQ.getMetadata(I, LLVMContext::MD_range))
       CR = CR.intersectWith(getConstantRangeFromMetadata(*Range));
 
   return CR;
 }
+
+static int64_t getOffsetFromIndex(const GEPOperator *GEP, unsigned Idx,
+                                  bool &VariableIdxFound,
+                                  const DataLayout &DL) {
+  // Skip over the first indices.
+  gep_type_iterator GTI = gep_type_begin(GEP);
+  for (unsigned i = 1; i != Idx; ++i, ++GTI)
+    /*skip along*/;
+
+  // Compute the offset implied by the rest of the indices.
+  int64_t Offset = 0;
+  for (unsigned i = Idx, e = GEP->getNumOperands(); i != e; ++i, ++GTI) {
+    ConstantInt *OpC = dyn_cast<ConstantInt>(GEP->getOperand(i));
+    if (!OpC)
+      return VariableIdxFound = true;
+    if (OpC->isZero())
+      continue; // No offset.
+
+    // Handle struct indices, which add their field offset to the pointer.
+    if (StructType *STy = GTI.getStructTypeOrNull()) {
+      Offset += DL.getStructLayout(STy)->getElementOffset(OpC->getZExtValue());
+      continue;
+    }
+
+    // Otherwise, we have a sequential type like an array or vector.  Multiply
+    // the index by the ElementSize.
+    uint64_t Size = DL.getTypeAllocSize(GTI.getIndexedType());
+    Offset += Size * OpC->getSExtValue();
+  }
+
+  return Offset;
+}
+
+bool llvm::isPointerOffset(Value *Ptr1, Value *Ptr2, int64_t &Offset,
+                           const DataLayout &DL) {
+  Ptr1 = Ptr1->stripPointerCasts();
+  Ptr2 = Ptr2->stripPointerCasts();
+
+  // Handle the trivial case first.
+  if (Ptr1 == Ptr2) {
+    Offset = 0;
+    return true;
+  }
+
+  GEPOperator *GEP1 = dyn_cast<GEPOperator>(Ptr1);
+  GEPOperator *GEP2 = dyn_cast<GEPOperator>(Ptr2);
+
+  bool VariableIdxFound = false;
+
+  // If one pointer is a GEP and the other isn't, then see if the GEP is a
+  // constant offset from the base, as in "P" and "gep P, 1".
+  if (GEP1 && !GEP2 && GEP1->getOperand(0)->stripPointerCasts() == Ptr2) {
+    Offset = -getOffsetFromIndex(GEP1, 1, VariableIdxFound, DL);
+    return !VariableIdxFound;
+  }
+
+  if (GEP2 && !GEP1 && GEP2->getOperand(0)->stripPointerCasts() == Ptr1) {
+    Offset = getOffsetFromIndex(GEP2, 1, VariableIdxFound, DL);
+    return !VariableIdxFound;
+  }
+
+  // Right now we handle the case when Ptr1/Ptr2 are both GEPs with an identical
+  // base.  After that base, they may have some number of common (and
+  // potentially variable) indices.  After that they handle some constant
+  // offset, which determines their offset from each other.  At this point, we
+  // handle no other case.
+  if (!GEP1 || !GEP2 || GEP1->getOperand(0) != GEP2->getOperand(0))
+    return false;
+
+  // Skip any common indices and track the GEP types.
+  unsigned Idx = 1;
+  for (; Idx != GEP1->getNumOperands() && Idx != GEP2->getNumOperands(); ++Idx)
+    if (GEP1->getOperand(Idx) != GEP2->getOperand(Idx))
+      break;
+
+  int64_t Offset1 = getOffsetFromIndex(GEP1, Idx, VariableIdxFound, DL);
+  int64_t Offset2 = getOffsetFromIndex(GEP2, Idx, VariableIdxFound, DL);
+  if (VariableIdxFound)
+    return false;
+
+  Offset = Offset2 - Offset1;
+  return true;
+}

llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp

 
 #define DEBUG_TYPE "memcpyopt"
 
 STATISTIC(NumMemCpyInstr, "Number of memcpy instructions deleted");
 STATISTIC(NumMemSetInfer, "Number of memsets inferred");
 STATISTIC(NumMoveToCpy,   "Number of memmoves converted to memcpy");
 STATISTIC(NumCpyToSet,    "Number of memcpys converted to memset");
 
-static int64_t GetOffsetFromIndex(const GEPOperator *GEP, unsigned Idx,
-                                  bool &VariableIdxFound,
-                                  const DataLayout &DL) {
-  // Skip over the first indices.
-  gep_type_iterator GTI = gep_type_begin(GEP);
-  for (unsigned i = 1; i != Idx; ++i, ++GTI)
-    /*skip along*/;
-
-  // Compute the offset implied by the rest of the indices.
-  int64_t Offset = 0;
-  for (unsigned i = Idx, e = GEP->getNumOperands(); i != e; ++i, ++GTI) {
-    ConstantInt *OpC = dyn_cast<ConstantInt>(GEP->getOperand(i));
-    if (!OpC)
-      return VariableIdxFound = true;
-    if (OpC->isZero()) continue;  // No offset.
-
-    // Handle struct indices, which add their field offset to the pointer.
-    if (StructType *STy = GTI.getStructTypeOrNull()) {
-      Offset += DL.getStructLayout(STy)->getElementOffset(OpC->getZExtValue());
-      continue;
-    }
-
-    // Otherwise, we have a sequential type like an array or vector.  Multiply
-    // the index by the ElementSize.
-    uint64_t Size = DL.getTypeAllocSize(GTI.getIndexedType());
-    Offset += Size*OpC->getSExtValue();
-  }
-
-  return Offset;
-}
-
-/// Return true if Ptr1 is provably equal to Ptr2 plus a constant offset, and
-/// return that constant offset. For example, Ptr1 might be &A[42], and Ptr2
-/// might be &A[40]. In this case offset would be -8.
-static bool IsPointerOffset(Value *Ptr1, Value *Ptr2, int64_t &Offset,
-                            const DataLayout &DL) {
-  Ptr1 = Ptr1->stripPointerCasts();
-  Ptr2 = Ptr2->stripPointerCasts();
-
-  // Handle the trivial case first.
-  if (Ptr1 == Ptr2) {
-    Offset = 0;
-    return true;
-  }
-
-  GEPOperator *GEP1 = dyn_cast<GEPOperator>(Ptr1);
-  GEPOperator *GEP2 = dyn_cast<GEPOperator>(Ptr2);
-
-  bool VariableIdxFound = false;
-
-  // If one pointer is a GEP and the other isn't, then see if the GEP is a
-  // constant offset from the base, as in "P" and "gep P, 1".
-  if (GEP1 && !GEP2 && GEP1->getOperand(0)->stripPointerCasts() == Ptr2) {
-    Offset = -GetOffsetFromIndex(GEP1, 1, VariableIdxFound, DL);
-    return !VariableIdxFound;
-  }
-
-  if (GEP2 && !GEP1 && GEP2->getOperand(0)->stripPointerCasts() == Ptr1) {
-    Offset = GetOffsetFromIndex(GEP2, 1, VariableIdxFound, DL);
-    return !VariableIdxFound;
-  }
-
-  // Right now we handle the case when Ptr1/Ptr2 are both GEPs with an identical
-  // base.  After that base, they may have some number of common (and
-  // potentially variable) indices.  After that they handle some constant
-  // offset, which determines their offset from each other.  At this point, we
-  // handle no other case.
-  if (!GEP1 || !GEP2 || GEP1->getOperand(0) != GEP2->getOperand(0))
-    return false;
-
-  // Skip any common indices and track the GEP types.
-  unsigned Idx = 1;
-  for (; Idx != GEP1->getNumOperands() && Idx != GEP2->getNumOperands(); ++Idx)
-    if (GEP1->getOperand(Idx) != GEP2->getOperand(Idx))
-      break;
-
-  int64_t Offset1 = GetOffsetFromIndex(GEP1, Idx, VariableIdxFound, DL);
-  int64_t Offset2 = GetOffsetFromIndex(GEP2, Idx, VariableIdxFound, DL);
-  if (VariableIdxFound) return false;
-
-  Offset = Offset2-Offset1;
-  return true;
-}
-
 namespace {
 
 /// Represents a range of memset'd bytes with the ByteVal value.
 /// This allows us to analyze stores like:
 ///   store 0 -> P+1
 ///   store 0 -> P+0
 ///   store 0 -> P+3
 ///   store 0 -> P+2
if (StoreInst *NextStore = dyn_cast<StoreInst>(BI)) {
       Value *StoredByte = isBytewiseValue(NextStore->getOperand(0), DL);
       if (isa<UndefValue>(ByteVal) && StoredByte)
         ByteVal = StoredByte;
       if (ByteVal != StoredByte)
         break;
 
       // Check to see if this store is to a constant offset from the start ptr.
       int64_t Offset;
-      if (!IsPointerOffset(StartPtr, NextStore->getPointerOperand(), Offset,
+      if (!isPointerOffset(StartPtr, NextStore->getPointerOperand(), Offset,
                            DL))
         break;
 
       Ranges.addStore(Offset, NextStore);
     } else {
       MemSetInst *MSI = cast<MemSetInst>(BI);
 
       if (MSI->isVolatile() || ByteVal != MSI->getValue() ||
           !isa<ConstantInt>(MSI->getLength()))
         break;
 
       // Check to see if this store is to a constant offset from the start ptr.
       int64_t Offset;
-      if (!IsPointerOffset(StartPtr, MSI->getDest(), Offset, DL))
+      if (!isPointerOffset(StartPtr, MSI->getDest(), Offset, DL))
         break;
 
       Ranges.addMemSet(Offset, MSI);
     }
   }
 
   // If we have no ranges, then we just had a single store with nothing that
   // could be merged in.  This is a very common case of course.