[llvm] [InstCombine] Propagate invariant.load metadata across unpacked loads (PR #152186)

[Fei Peng via llvm-commits]

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@@ -718,6 +718,14 @@ static Instruction *combineLoadToOperationType(InstCombinerImpl &IC,
   return nullptr;
 }
 
+// Check if the aggregate load has a invariant.load metadata
+// If aggregate load has invariant.load metadata, add it to the
+// unpacked loads as well.
+static void copyInvariantLoadMetadata(LoadInst &LI, LoadInst *NewLoad) {
+  if (MDNode *MD = LI.getMetadata("invariant.load"))
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fiigii wrote:

`copyMetadataForLoad` sounds like only designed for load type casting. And some code that checks `NewType->isPointerTy()` implicitly assumes the OldType is  also a pointer, which sounds incorrect for spliting loads.
```
    // Note, essentially every kind of metadata should be preserved here! This
    // routine is supposed to clone a load instruction changing *only its type*.
    // The only metadata it makes sense to drop is metadata which is invalidated
    // when the pointer type changes. This should essentially never be the case
    // in LLVM, but we explicitly switch over only known metadata to be
    // conservatively correct. If you are adding metadata to LLVM which pertains
    // to loads, you almost certainly want to add it here.
   ```

Shall we add a `copyMetadataForSplitLoad`?

https://github.com/llvm/llvm-project/pull/152186