[PATCH] D58626: [DAG] Fix constant store folding to handle non-byte sizes.

[Clement Courbet via Phabricator via llvm-commits]

courbet added inline comments.


================
Comment at: llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp:15436
         // be used as data sinks.
-        if (STBase.contains(STByteSize, ChainBase, ChainByteSize, DAG)) {
+        if (STBase.contains((STBitSize+7)/8, ChainBase, (ChainBitSize+7)/8, DAG)) {
           CombineTo(ST1, ST1->getChain());
----------------
This is overly optimistic: for example, this will return true for STBitSize = 1 and ChainBitSize= 2 if both are at offset 0

What about passing size in bits to BaseIndexOffset::contains() and letting it do the computation in bits:

```
bool BaseIndexOffset::contains(int64_t BitSize, const BaseIndexOffset &Other,
                               int64_t OtherBitSize, const SelectionDAG &DAG,
                               int64_t &Offset) const {
  if (!equalBaseIndex(Other, DAG, Offset))
    return false;
  if (Offset >= 0) {
    // Other is after *this:
    // [-------*this---------]
    //            [---Other--]
    // ==Offset==>
    return 8 * Offset + OtherBitSize <= BitSize;
  }
  // Other starts strictly before *this, it cannot be fully contained.
  //    [-------*this---------]
  // [--Other--]
  return false;
}
```




Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D58626/new/

https://reviews.llvm.org/D58626