[llvm] [DataLayout] Add isNullPointerAllZeroes (PR #165314)

[Alexander Richardson via llvm-commits]

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@@ -398,6 +398,12 @@ class DataLayout {
            PS.HasExternalState;
   }
 
+  /// Returns if the null pointer for this address space has an all-zero bit
+  /// representation.
+  bool isNullPointerAllZeroes(unsigned AddrSpace) const {
+    return AddrSpace == 0;
+  }
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arichardson wrote:

That said, it probably doesn't matter too much what we use since it will have to change again for #131557 , the main thing I would like to see is avoiding ==0 checks which this patch achieves as is so IMO no need to do something generic.

https://github.com/llvm/llvm-project/pull/165314