[llvm] [DOC][GlobalIsel] Add description for G_FREEZE (PR #156707)

[Shaoce SUN via llvm-commits]

https://github.com/sunshaoce created https://github.com/llvm/llvm-project/pull/156707

Description based on https://llvm.org/docs/LangRef.html#id333

>From bee06ab9d8a6af3ac45f7d97ef4ee517ce1c959e Mon Sep 17 00:00:00 2001
From: Shaoce SUN <sunshaoce at outlook.com>
Date: Thu, 4 Sep 2025 00:11:59 +0800
Subject: [PATCH] [DOC][GlobalIsel] Add description for G_FREEZE

---
 llvm/docs/GlobalISel/GenericOpcode.rst | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/llvm/docs/GlobalISel/GenericOpcode.rst b/llvm/docs/GlobalISel/GenericOpcode.rst
index eefd76de9c33a..b055327466739 100644
--- a/llvm/docs/GlobalISel/GenericOpcode.rst
+++ b/llvm/docs/GlobalISel/GenericOpcode.rst
@@ -1150,6 +1150,15 @@ An alignment value of `0` or `1` means no specific alignment.
 
   %8:_(p0) = G_DYN_STACKALLOC %7(s64), 32
 
+G_FREEZE
+^^^^^^^^
+
+G_FREEZE is used to stop propagation of undef and poison values.
+
+.. code-block:: none
+
+  %1:_(s32) = G_FREEZE %0(s32)
+
 Optimization Hints
 ------------------