[PATCH] D71207: [NFC] Use SelectionDAG::getMemBasePlusOffset() instead of getNode(ISD::ADD)

[Alexander Richardson via Phabricator via llvm-commits]

arichardson created this revision.
arichardson added a reviewer: spatel.
Herald added subscribers: llvm-commits, hiraditya.
Herald added a project: LLVM.
arichardson added a parent revision: D71206: [NFC] Implement SelectionDAG::getObjectPtrOffset() using getMemBasePlusOffset().

To find potential opportunities to use getMemBasePlusOffset() I looked at
all ISD::ADD uses found with the regex getNode\(ISD::ADD,.+,.+Ptr
in lib/CodeGen/SelectionDAG. If this patch is accepted I will convert
the files in the individual backends too.

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.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D71207

Files:
  llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
  llvm/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp
  llvm/lib/CodeGen/SelectionDAG/LegalizeIntegerTypes.cpp
  llvm/lib/CodeGen/SelectionDAG/LegalizeTypesGeneric.cpp
  llvm/lib/CodeGen/SelectionDAG/LegalizeVectorTypes.cpp
  llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
  llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp

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