[llvm] [llvm][RISCV] Support P Extension CodeGen (PR #190303)

[Kito Cheng via llvm-commits]

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@@ -1796,10 +1796,26 @@ let Predicates = [HasStdExtP] in {
   // Basic 8-bit arithmetic patterns
   def : PatGprGpr<add, PADD_B, XLenVecI8VT>;
   def : PatGprGpr<sub, PSUB_B, XLenVecI8VT>;
+  def : Pat<(XLenVecI8VT
+              (add (XLenVecI8VT GPR:$rs1),
+                   (XLenVecI8VT (splat_vector (XLenVT GPR:$rs2))))),
+            (PADD_BS GPR:$rs1, GPR:$rs2)>;
+  def : Pat<(XLenVecI8VT
+              (add (XLenVecI8VT (splat_vector (XLenVT GPR:$rs2))),
+                   (XLenVecI8VT GPR:$rs1))),
+            (PADD_BS GPR:$rs1, GPR:$rs2)>;
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kito-cheng wrote:

1. I am not family with DAG stuffs, do we need those two variants? I mean add has marked as SDNPCommutative, I thought LLVM should be able to do that automatically?

2. Maybe add a PatGprSplatGpr class like PatGprGpr? I assume we need to add few more `*.*s` patterns?

https://github.com/llvm/llvm-project/pull/190303