[llvm] [NFCI][IR] Add optional DataLayout argument to zero and null value related APIs (PR #183208)

[Shilei Tian via llvm-commits]

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@@ -52,7 +53,10 @@ class Constant : public User {
   Constant(const Constant &) = delete;
 
   /// Return true if this is the value that would be returned by getNullValue.
-  LLVM_ABI bool isNullValue() const;
+  LLVM_ABI bool isNullValue(const DataLayout *DL = nullptr) const;
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shiltian wrote:

well, we have to though, because the current `getNullValue` will simply return `ConstantAggregateZero` for any aggregate types, but this will no longer be the case after we change the semantics. We will have to recursively construct null/zero value accordingly.

https://github.com/llvm/llvm-project/pull/183208