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

[Fehr Mathieu via llvm-commits]

https://github.com/math-fehr created https://github.com/llvm/llvm-project/pull/134325

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.

>From 241ec8357846a98b37a89f2e34eaeeb185566d8c Mon Sep 17 00:00:00 2001
From: Mathieu Fehr <mathieu.fehr at gmail.com>
Date: Fri, 4 Apr 2025 01:40:14 +0100
Subject: [PATCH] [LangRef] Clarify semantics for ``sdiv poison -1``

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 explicitely.
---
 llvm/docs/LangRef.rst | 2 ++
 1 file changed, 2 insertions(+)

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.