[Docs] Store to poison is the canonical form for non-terminator unreachable (#98910)

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Differential Revision: https://phabricator.intern.facebook.com/D60251667

Author: dianqk

llvm/docs/Frontend/PerformanceTips.rst

@@ -206,7 +206,9 @@ Other Things to Consider
    that fact is critical for optimization purposes.  Assumes are a great
    prototyping mechanism, but they can have negative effects on both compile
    time and optimization effectiveness.  The former is fixable with enough
-   effort, but the later is fairly fundamental to their designed purpose.
+   effort, but the later is fairly fundamental to their designed purpose.  If
+   you are creating a non-terminator unreachable instruction or passing a false
+   value, use the ``store i1 true, ptr poison, align 1`` canonical form.
 
 
 Describing Language Specific Properties