[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:

That sounds like a bit of a contradiction still, since bitcast iN to byte to ptr is valid but bitcast iN to ptr isn't legal, so looking through bitcast seems to become illegal, which seems a bigger structural change. Sorry this is probably not a good place to reopen that discussion, but I'd have thought that LLVM would need to instead go with permitting inttoptr to allow byte type inputs, to avoid pre-existing passes, which currently step through bitcast as noops, silently becoming unsound.

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