[llvm] [IR] Add `samesign` flag to icmp instruction (PR #111419)

[Yingwei Zheng via llvm-commits]

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@@ -12398,6 +12399,9 @@ If the operands are integer vectors, then they are compared element by
 element. The result is an ``i1`` vector with the same number of elements
 as the values being compared. Otherwise, the result is an ``i1``.
 
+If the ``samesign`` keyword is present and the operands are not of the
+same sign then the result is a :ref:`poison value <poisonvalues>`.
+
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dtcxzyw wrote:

Should we note here we only infer `samesign` on unsigned predicates?


https://github.com/llvm/llvm-project/pull/111419