[llvm] [IR] Allow fast math flags on calls with homogeneous FP struct types (PR #110506)

[Matt Arsenault via llvm-commits]

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@@ -12472,9 +12472,8 @@ instruction's return value on the same edge).
 The optional ``fast-math-flags`` marker indicates that the phi has one
 or more :ref:`fast-math-flags <fastmath>`. These are optimization hints
 to enable otherwise unsafe floating-point optimizations. Fast-math-flags
-are only valid for phis that return a floating-point scalar or vector
-type, or an array (nested to any depth) of floating-point scalar or vector
-types.
+are only valid for phis that return a floating-point scalar or vector type,
+possibly within an array (nested to any depth), or a homogeneous struct literal.
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arsenm wrote:

Remove "possibly", and elaborate on what a homogenous struct means (also it's not a literal?)

https://github.com/llvm/llvm-project/pull/110506