[llvm] [LV] Get FMFs from VectorBuilder in createSimpleReduction. NFC (PR #132017)

[Florian Hahn via llvm-commits]

================
@@ -87,6 +87,9 @@ class VectorBuilder {
     StaticVectorLength = ElementCount::getFixed(NewFixedVL);
     return *this;
   }
+
+  FastMathFlags &getFastMathFlags() const { return Builder.getFastMathFlags(); }
----------------
fhahn wrote:

Might be good to return `const FastMathFlags` and document

https://github.com/llvm/llvm-project/pull/132017