[NFC] Add a SDValue overload for SelectionDAG::getMemBasePlusOffset()

[arichardson]

Summary

This change is preparatory work to use this helper functions in more places.
Currently the function only allows integer constants offsets, but there
are cases where we can use an existing SDValue parameter.

The motivation for this change is our out-of-tree CHERI backend
(https://github.com/CTSRD-CHERI/llvm-project). We use a separate register
type to store pointers (128-bit capabilities, which are effectively
unforgeable and monotonic fat pointers). These capabilities permit a
reduced set of operations and therefore use a separate ValueType (iFATPTR).
to represent pointers implemented as capabilities.
Therefore, we need to avoid using ISD::ADD for our patterns that operate
on pointers and need to use a function that chooses ISD::ADD or a new
ISD::PTRADD opcode depending on the value type.

We originally added a new DAG.getPointerAdd() function, but after this
patch series we can modify the implementation of getMemBasePlusOffset()
instead. Avoiding direct uses of ISD::ADD for pointer types will
significantly reduce the amount of assertion/instruction selection
failures for us in future upstream merges.

[merge_guards_bot]

Build result: FAILURE - Could not check out parent git hash "86e5d7fcd6891e259e9e8df15f579ab8428d0c5a". It was not found in the repository. Did you configure the "Parent Revision" in Phabricator properly? Trying to apply the patch to the master branch instead...

ERROR: arc patch failed with error code 1. Check build log for details.
Log files: console-log.txt, CMakeCache.txt

[spatel]

LGTM

[craig.topper]

llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp

5738–5745

Should we rewrite this in terms of the new function? Perhaps by moving to the header file.

[arichardson]

llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp

5738–5745

Yes, will do.
I'm not sure if I adding it to the header is beneficial compared to having it in the .cpp.

In our fork we depend on TargetLowering, so we need to have the function in the .cpp rather than the .h, but I can obviously keep that change downstream.

For context here is our implementation that handles CHERI capabilities: https://github.com/CTSRD-CHERI/llvm-project/blob/8cad6d336ad9e91657db9999fcd25adceae3be83/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp#L6297

[arichardson]

Implement using the other overload

[merge_guards_bot]

Unit tests: pass. 60837 tests passed, 0 failed and 726 were skipped.

clang-format: pass.

Build artifacts: console-log.txt, CMakeCache.txt, test-results.xml, diff.json

[craig.topper]

LGTM

llvm/include/llvm/CodeGen/SelectionDAG.h

#endif
   SDValue getTruncStore(SDValue Chain, const SDLoc &dl, SDValue Val,
                         SDValue Ptr, EVT SVT, MachineMemOperand *MMO);
   SDValue getIndexedStore(SDValue OrigStore, const SDLoc &dl, SDValue Base,
                           SDValue Offset, ISD::MemIndexedMode AM);
 
   /// Returns sum of the base pointer and offset.
   /// Unlike getObjectPtrOffset this does not set NoUnsignedWrap by default.
   SDValue getMemBasePlusOffset(SDValue Base, int64_t Offset, const SDLoc &DL);
+  SDValue getMemBasePlusOffset(SDValue Base, SDValue Offset, const SDLoc &DL);
 
   SDValue getMaskedLoad(EVT VT, const SDLoc &dl, SDValue Chain, SDValue Base,
                         SDValue Offset, SDValue Mask, SDValue Src0, EVT MemVT,
                         MachineMemOperand *MMO, ISD::MemIndexedMode AM,
                         ISD::LoadExtType, bool IsExpanding = false);
   SDValue getIndexedMaskedLoad(SDValue OrigLoad, const SDLoc &dl, SDValue Base,
                                SDValue Offset, ISD::MemIndexedMode AM);
   SDValue getMaskedStore(SDValue Chain, const SDLoc &dl, SDValue Val,

llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp

static SDValue getMemsetStringVal(EVT VT, const SDLoc &dl, SelectionDAG &DAG,
   if (TLI.shouldConvertConstantLoadToIntImm(Val, Ty))
     return DAG.getConstant(Val, dl, VT);
   return SDValue(nullptr, 0);
 }
 
 SDValue SelectionDAG::getMemBasePlusOffset(SDValue Base, int64_t Offset,
                                            const SDLoc &DL) {
   EVT VT = Base.getValueType();
-  return getNode(ISD::ADD, DL, VT, Base, getConstant(Offset, DL, VT));
+  return getMemBasePlusOffset(Base, getConstant(Offset, DL, VT), DL);
+}
+
+SDValue SelectionDAG::getMemBasePlusOffset(SDValue Ptr, SDValue Offset,
+                                           const SDLoc &DL) {
+  assert(Offset.getValueType().isInteger());
+  EVT BasePtrVT = Ptr.getValueType();
+  return getNode(ISD::ADD, DL, BasePtrVT, Ptr, Offset);
 }
 
 /// Returns true if memcpy source is constant data.
 static bool isMemSrcFromConstant(SDValue Src, ConstantDataArraySlice &Slice) {
   uint64_t SrcDelta = 0;
   GlobalAddressSDNode *G = nullptr;
   if (Src.getOpcode() == ISD::GlobalAddress)
     G = cast<GlobalAddressSDNode>(Src);