[llvm] [IRBuilder][GlobalISel] Add byte ptr cast support in IRBuilder (PR #222049)

[Jameson Nash via llvm-commits]

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@@ -140,9 +146,7 @@ Value *IRBuilderBase::CreateBitPreservingCastChain(const DataLayout &DL,
   };
 
   // See if we need inttoptr for this type pair. May require additional bitcast.
-  bool OldIsIntLike =
-      OldTy->isIntOrIntVectorTy() || OldTy->isByteOrByteVectorTy();
-  if (OldIsIntLike && NewTy->isPtrOrPtrVectorTy()) {
+  if (OldTy->isIntOrIntVectorTy() && NewTy->isPtrOrPtrVectorTy()) {
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vtjnash wrote:

@nikic, the LangRef very literally says "It is always a no-op." today. I think I understand what you meant (I'm guessing it is because bitcasts cause poison to spread, so the optimizer can add bitcast to byte but not from byte), but this still sounds a fairly sweeping change to make because of the ptr-to-ptr legacy baggage.

(combining inttotpr/ptrtoint/bitcast sounds nice for eventually also solving this from the other direction, of just defining that all same-size casts are legal)

https://github.com/llvm/llvm-project/pull/222049