[llvm] [Docs] Clarify that `reassoc` isn't just for reassociation (PR #133168)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-ir

Author: Chris B (llvm-beanz)

<details>
<summary>Changes</summary>

The `reassoc` fast-math flag allows a much wider array of algebraic transformations than just strictly reassociations. In some cases it does commutations, or distributions.

While it might make sense to fix the flag naming at some point, in the meantime we should at least have the docs be accurate to avoid confusion.

---
Full diff: https://github.com/llvm/llvm-project/pull/133168.diff


1 Files Affected:

- (modified) llvm/docs/LangRef.rst (+3-2) 


``````````diff
diff --git a/llvm/docs/LangRef.rst b/llvm/docs/LangRef.rst
index 655ec4389456c..c505aff34da31 100644
--- a/llvm/docs/LangRef.rst
+++ b/llvm/docs/LangRef.rst
@@ -3971,8 +3971,9 @@ output, given the original flags.
    for places where this can apply to LLVM's intrinsic math functions.
 
 ``reassoc``
-   Allow reassociation transformations for floating-point instructions.
-   This may dramatically change results in floating-point.
+   Allow algebraically equivalent transformations for floating-point
+   instructions such as reassociation transformations. This may dramatically
+   change results in floating-point.
 
 .. _uselistorder:
 

``````````

</details>


https://github.com/llvm/llvm-project/pull/133168