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

[Ramkumar Ramachandra via llvm-commits]

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@@ -208,7 +208,7 @@ template <typename Pred> struct Not {
 template <typename Pred> Not(const Pred &P) -> Not<Pred>;
 
 /// Match if the inner pattern does NOT match.
-template <typename Pred> inline Not<Pred> m_Unless(const Pred &P) {
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artagnon wrote:

See line 49 of PatternMatch.h:

```cpp
using namespace llvm::PatternMatchHelpers;
```

The PatternMatchHelpers namespace can obviously not be nested within PatternMatch, because it's used by SCEV/VPlanPatternMatch as well, so the only "solution" is to never include PatternMatch.h within spaces that have an incompatible PatternMatch (eg. SDAG).

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