[llvm] [DAG] SDPatternMatch - add a m_SpecificNeg() matcher (PR #173807)

[Min-Yih Hsu via llvm-commits]

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@@ -1299,6 +1299,32 @@ inline BinaryOpc_match<ValTy, AllOnes_match, true> m_Not(const ValTy &V) {
   return m_Xor(V, m_AllOnes());
 }
 
+struct SpecificNeg_match {
+  SDValue V;
+
+  explicit SpecificNeg_match(SDValue V) : V(V) {}
+
+  template <typename MatchContext>
+  bool match(const MatchContext &Ctx, SDValue N) {
+    if (sd_context_match(N, Ctx, m_Neg(m_Specific(V))))
+      return true;
+
+    return ISD::matchBinaryPredicate(
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mshockwave wrote:

>  i think keeping them separate is cleaner.
> it doesn't change the existing behavior of m_Neg which is purely structural

I also think we should keep them separate, to avoid confusion and/or potential foot gun in the future

https://github.com/llvm/llvm-project/pull/173807