[llvm] [DAG] Add `SDPatternMatch::m_Load` (PR #145481)

[Min-Yih Hsu via llvm-commits]

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@@ -513,6 +513,12 @@ m_VSelect(const T0_P &Cond, const T1_P &T, const T2_P &F) {
   return TernaryOpc_match<T0_P, T1_P, T2_P>(ISD::VSELECT, Cond, T, F);
 }
 
+template <typename T0_P, typename T1_P, typename T2_P>
+inline TernaryOpc_match<T0_P, T1_P, T2_P>
+m_Load(const T0_P &Ch, const T1_P &Ptr, const T2_P &Offset) {
+  return TernaryOpc_match<T0_P, T1_P, T2_P>(ISD::LOAD, Ch, Ptr, Offset);
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mshockwave wrote:

I think having a way to distinguish which (SDValue) result to match would indeed be helpful. For instance, to match a SDNode with optional input chain, we can't tell if operand 0 is a chain or not, other than something like `m_AllOf(m_SpecificVT(MVT::Other), <matcher for operand 0>)` or using a matching class that uses `EffectiveOperand`, which skips over chains and glues (but not every matching classes use it).

Not necessary for this patch, but we might want a more general solution, for instance `m_Result<0>(m_Load(...))` for matching the first result of a load.

https://github.com/llvm/llvm-project/pull/145481