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

[Artem Belevich 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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Artem-B wrote:

If the choice was between alloca in generic AS and alloca in AS(5), then indeed the choice would be to cast or skip.
However, considering that alloca's AS can be explicitly specified to be in any AS, it would be prudent to have an assertion, so we catch unexpected input early, at the point where we care about it.

If we don't have an assertion, and we get an alloca in AS 333, we'll happily insert an ASC which will cause lowering problems further down in the pipeline and whoever will have to debug that will have to back-track to here before moving on to the real root cause -- nonsensical input IR. I'd much rather break things here, as soon as we're aware that something is wrong.


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