[llvm] [NVPTX] Check Before inserting AddrSpaceCastInst in NVPTXLoweringAlloca (PR #106127)

[Jeff Niu via llvm-commits]

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@@ -72,12 +72,21 @@ bool NVPTXLowerAlloca::runOnFunction(Function &F) {
         Changed = true;
         auto ETy = allocaInst->getAllocatedType();
         auto LocalAddrTy = PointerType::get(ETy, ADDRESS_SPACE_LOCAL);
-        auto NewASCToLocal = new AddrSpaceCastInst(allocaInst, LocalAddrTy, "");
-        auto GenericAddrTy = PointerType::get(ETy, ADDRESS_SPACE_GENERIC);
-        auto NewASCToGeneric =
-            new AddrSpaceCastInst(NewASCToLocal, GenericAddrTy, "");
-        NewASCToLocal->insertAfter(allocaInst);
-        NewASCToGeneric->insertAfter(NewASCToLocal);
+        PointerType *AllocInstPtrTy =
+            cast<PointerType>(allocaInst->getType()->getScalarType());
+        Instruction *NewASCToGeneric = allocaInst;
+        if (AllocInstPtrTy->getAddressSpace() != ADDRESS_SPACE_LOCAL) {
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Mogball wrote:

@Artem-B Separating concerns here:

1. Does the PTX spec place the upstream requirements that allocas must be allocated in the generic address space instead of LOCAL? (I imagine if there is reg spilling), or is this an implementation detail of the LLVM backend?
2. If it is the latter, what do you think the LLVM backend's policy should be?

https://github.com/llvm/llvm-project/pull/106127