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

[Benjamin Maxwell via cfe-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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MacDue wrote:

I've listed the cases under the "Fast-Math Flags" section and updated the instructions to reference that. I think that's a little clearer than trying to squash call the cases into a single sentence (and makes future updates easier). 

I've also updated one of the struct examples to point out it's a homogeneous struct. 

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