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

[Simon Pilgrim via llvm-commits]

================
@@ -230,6 +236,9 @@ TEST_F(SelectionDAGPatternMatchTest, matchTernaryOp) {
   EXPECT_FALSE(sd_match(
       InsertSubvector,
       m_InsertSubvector(m_Specific(V2), m_Specific(V3), m_SpecificInt(3))));
+
+  EXPECT_TRUE(sd_match(
+      Load, m_Load(m_Specific(Ch), m_Specific(BasePtr), m_Specific(Offset))));
----------------
RKSimon wrote:

We need an extra test:
```
EXPECT_FALSE(sd_match(
      SDValue(Load.getNode(), 1), m_Load(m_Specific(Ch), m_Specific(BasePtr), m_Specific(Offset))));
```

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