[llvm] [TargetLowering] Add a new function `getNullPtrValue` (PR #126665)

[Nikita Popov via llvm-commits]

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@@ -1807,8 +1807,7 @@ SDValue SelectionDAGBuilder::getValueImpl(const Value *V) {
 
     if (isa<ConstantPointerNull>(C)) {
       unsigned AS = V->getType()->getPointerAddressSpace();
-      return DAG.getConstant(0, getCurSDLoc(),
-                             TLI.getPointerTy(DAG.getDataLayout(), AS));
+      return TLI.getNullPtrValue(AS, getCurSDLoc(), DAG);
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nikic wrote:

I'm not sure what your godbolt link is trying to show, it doesn't have an addrspace cast?

Here you can see that InstCombine does not fold addrspacecast of null: https://godbolt.org/z/jrq8a8vez There is no assumption that a zero value in one address space maps to a zero value in another.

https://github.com/llvm/llvm-project/pull/126665