[llvm] [LangRef] Clarify semantics for ``sdiv poison -1`` (PR #134325)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-ir

Author: Fehr Mathieu (math-fehr)

<details>
<summary>Changes</summary>

Documents in the LangRef that ``sdiv poison -1`` triggers immediate undefined behavior.

Despite it being already documented in "immediate undefined behavior occurs if a poison value is used as an instruction operand that has any values that trigger undefined behavior", it is a corner case that is worth mentioning explicitly.

---
Full diff: https://github.com/llvm/llvm-project/pull/134325.diff


1 Files Affected:

- (modified) llvm/docs/LangRef.rst (+2) 


``````````diff
diff --git a/llvm/docs/LangRef.rst b/llvm/docs/LangRef.rst
index 806874fa76b2e..6e4cee926af9c 100644
--- a/llvm/docs/LangRef.rst
+++ b/llvm/docs/LangRef.rst
@@ -4917,6 +4917,8 @@ behavior. Notably this includes (but is not limited to):
    space).
 -  The divisor operand of a ``udiv``, ``sdiv``, ``urem`` or ``srem``
    instruction.
+-  The dividend operand of a ``sdiv`` or ``srem`` instruction when the divisor
+   is -1.
 -  The condition operand of a :ref:`br <i_br>` instruction.
 -  The callee operand of a :ref:`call <i_call>` or :ref:`invoke <i_invoke>`
    instruction.

``````````

</details>


https://github.com/llvm/llvm-project/pull/134325