[llvm] [PatternMatchHelpers] Introduce m_Unless (NFC) (PR #212454)

[Florian Hahn via llvm-commits]

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@@ -2781,10 +2781,8 @@ void VPlanTransforms::dropPoisonGeneratingRecipes(VPlan &Plan) {
   // wrapped in a Reverse, which is just a permutation of the header mask, so
   // peel it off before checking. The header mask is still the abstract region
   // value at this point (materialization happens later).
-  auto IsNotHeaderMask = [](VPValue *Mask) {
-    return Mask &&
-           !match(Mask, m_CombineOr(m_HeaderMask(), m_Reverse(m_HeaderMask())));
-  };
+  auto m_UnlessHdrMask = m_Unless( // NOLINT
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fhahn wrote:

Ah right, but here `m_UnlessHdrMask` is not a generic matcher any more, so could also just be `UnlessHdrMask`?

https://github.com/llvm/llvm-project/pull/212454