[IR] Add utilities for manipulating length of MemIntrinsic [nfc]

llvm/include/llvm/IR/IntrinsicInst.h

@@ -987,6 +987,13 @@ template <typename Derived> class MemIntrinsicBase : public IntrinsicInst {
   const Use &getLengthUse() const { return getArgOperandUse(ARG_LENGTH); }
   Use &getLengthUse() { return getArgOperandUse(ARG_LENGTH); }
 
+  std::optional<APInt> getLengthInBytes() const {
+    ConstantInt *C = dyn_cast<ConstantInt>(getLength());
+    if (!C)
+      return std::nullopt;
+    return C->getValue();
+  }
+
   /// This is just like getRawDest, but it strips off any cast
   /// instructions (including addrspacecast) that feed it, giving the
   /// original input.  The returned value is guaranteed to be a pointer.
@@ -1022,6 +1029,10 @@ template <typename Derived> class MemIntrinsicBase : public IntrinsicInst {
            "setLength called with value of wrong type!");
     setArgOperand(ARG_LENGTH, L);
   }
+
+  void setLength(uint64_t L) {
+    setLength(ConstantInt::get(getLength()->getType(), L));
+  }
 };
 
 /// Common base class for all memory transfer intrinsics. Simply provides

llvm/lib/CodeGen/SafeStack.cpp

@@ -262,7 +262,7 @@ bool SafeStack::IsMemIntrinsicSafe(const MemIntrinsic *MI, const Use &U,
       return true;
   }
 
-  const auto *Len = dyn_cast<ConstantInt>(MI->getLength());
+  auto Len = MI->getLengthInBytes();
   // Non-constant size => unsafe. FIXME: try SCEV getRange.
   if (!Len) return false;
   return IsAccessSafe(U, Len->getZExtValue(), AllocaPtr, AllocaSize);

llvm/lib/Transforms/IPO/AttributorAttributes.cpp

@@ -2008,9 +2008,8 @@ struct AAPointerInfoCallSiteArgument final : AAPointerInfoFloating {
     // destination) and second (=source) arguments as we know how they are
     // accessed.
     if (auto *MI = dyn_cast_or_null<MemIntrinsic>(getCtxI())) {
-      ConstantInt *Length = dyn_cast<ConstantInt>(MI->getLength());
       int64_t LengthVal = AA::RangeTy::Unknown;
-      if (Length)
+      if (auto Length = MI->getLengthInBytes())
         LengthVal = Length->getSExtValue();
       unsigned ArgNo = getIRPosition().getCallSiteArgNo();
       ChangeStatus Changed = ChangeStatus::UNCHANGED;

llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp

@@ -133,15 +133,15 @@ Instruction *InstCombinerImpl::SimplifyAnyMemTransfer(AnyMemTransferInst *MI) {
   // wouldn't be constant), and this must be a noop.
   if (!isModSet(AA->getModRefInfoMask(MI->getDest()))) {
     // Set the size of the copy to 0, it will be deleted on the next iteration.
-    MI->setLength(Constant::getNullValue(MI->getLength()->getType()));
+    MI->setLength((uint64_t)0);
     return MI;
   }
 
   // If the source is provably undef, the memcpy/memmove doesn't do anything
   // (unless the transfer is volatile).
   if (hasUndefSource(MI) && !MI->isVolatile()) {
     // Set the size of the copy to 0, it will be deleted on the next iteration.
-    MI->setLength(Constant::getNullValue(MI->getLength()->getType()));
+    MI->setLength((uint64_t)0);
     return MI;
   }
 
@@ -211,7 +211,7 @@ Instruction *InstCombinerImpl::SimplifyAnyMemTransfer(AnyMemTransferInst *MI) {
   }
 
   // Set the size of the copy to 0, it will be deleted on the next iteration.
-  MI->setLength(Constant::getNullValue(MemOpLength->getType()));
+  MI->setLength((uint64_t)0);
   return MI;
 }
 
@@ -229,7 +229,7 @@ Instruction *InstCombinerImpl::SimplifyAnyMemSet(AnyMemSetInst *MI) {
   // wouldn't be constant), and this must be a noop.
   if (!isModSet(AA->getModRefInfoMask(MI->getDest()))) {
     // Set the size of the copy to 0, it will be deleted on the next iteration.
-    MI->setLength(Constant::getNullValue(MI->getLength()->getType()));
+    MI->setLength((uint64_t)0);
     return MI;
   }
 
@@ -238,7 +238,7 @@ Instruction *InstCombinerImpl::SimplifyAnyMemSet(AnyMemSetInst *MI) {
   // value. Change to PoisonValue once #52930 is resolved.
   if (isa<UndefValue>(MI->getValue())) {
     // Set the size of the copy to 0, it will be deleted on the next iteration.
-    MI->setLength(Constant::getNullValue(MI->getLength()->getType()));
+    MI->setLength((uint64_t)0);
     return MI;
   }
 
@@ -279,7 +279,7 @@ Instruction *InstCombinerImpl::SimplifyAnyMemSet(AnyMemSetInst *MI) {
       S->setOrdering(AtomicOrdering::Unordered);
 
     // Set the size of the copy to 0, it will be deleted on the next iteration.
-    MI->setLength(Constant::getNullValue(LenC->getType()));
+    MI->setLength((uint64_t)0);
     return MI;
   }
 
@@ -1753,9 +1753,9 @@ Instruction *InstCombinerImpl::visitCallInst(CallInst &CI) {
   // Intrinsics cannot occur in an invoke or a callbr, so handle them here
   // instead of in visitCallBase.
   if (auto *MI = dyn_cast<AnyMemIntrinsic>(II)) {
-    if (ConstantInt *NumBytes = dyn_cast<ConstantInt>(MI->getLength())) {
+    if (auto NumBytes = MI->getLengthInBytes()) {
       // memmove/cpy/set of zero bytes is a noop.
-      if (NumBytes->isNullValue())
+      if (NumBytes->isZero())
         return eraseInstFromFunction(CI);
 
       // For atomic unordered mem intrinsics if len is not a positive or

llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp

@@ -685,15 +685,13 @@ static bool tryToShorten(Instruction *DeadI, int64_t &DeadStart,
                     << "\n  KILLER [" << ToRemoveStart << ", "
                     << int64_t(ToRemoveStart + ToRemoveSize) << ")\n");
 
-  Value *DeadWriteLength = DeadIntrinsic->getLength();
-  Value *TrimmedLength = ConstantInt::get(DeadWriteLength->getType(), NewSize);
-  DeadIntrinsic->setLength(TrimmedLength);
+  DeadIntrinsic->setLength(NewSize);
   DeadIntrinsic->setDestAlignment(PrefAlign);
 
   Value *OrigDest = DeadIntrinsic->getRawDest();
   if (!IsOverwriteEnd) {
     Value *Indices[1] = {
-        ConstantInt::get(DeadWriteLength->getType(), ToRemoveSize)};
+        ConstantInt::get(DeadIntrinsic->getLength()->getType(), ToRemoveSize)};
     Instruction *NewDestGEP = GetElementPtrInst::CreateInBounds(
         Type::getInt8Ty(DeadIntrinsic->getContext()), OrigDest, Indices, "",
         DeadI->getIterator());

llvm/lib/Transforms/Scalar/SROA.cpp

@@ -3425,8 +3425,7 @@ class AllocaSliceRewriter : public InstVisitor<AllocaSliceRewriter, bool> {
 
       // Rewrite the size as needed.
       if (NewEndOffset != EndOffset)
-        II.setLength(ConstantInt::get(II.getLength()->getType(),
-                                      NewEndOffset - NewBeginOffset));
+        II.setLength(NewEndOffset - NewBeginOffset);
       return false;
     }
     // Record this instruction for deletion.