[IR] Add utilities for manipulating length of MemIntrinsic [nfc] (#153856)

Goal is simply to reduce direct usage of getLength and setLength so that
if we end up moving memset.pattern (whose length is in elements) there
are fewer places to audit.

Author: preames

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;
   }
 
@@ -277,7 +277,7 @@ 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;
   }
 
@@ -1751,9 +1751,9 @@ 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

@@ -676,15 +676,13 @@ 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

@@ -3411,8 +3411,7 @@ 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.