[llvm] [RISCV] Move performCombineVMergeAndVOps into RISCVFoldMasks (PR #71764)

[Wang Pengcheng via llvm-commits]

================
@@ -9,15 +9,29 @@
 // This pass performs various peephole optimisations that fold masks into vector
 // pseudo instructions after instruction selection.
 //
-// Currently it converts
-// PseudoVMERGE_VVM %false, %false, %true, %allonesmask, %vl, %sew
+// It performs the following transforms:
+//
+// %true = PseudoFOO %passthru, ..., %vl, %sew
+// %x = PseudoVMERGE_VVM %passthru, %passthru, %true, %mask, %vl, %sew
+// ->
+// %x = PseudoFOO_MASK %false, ..., %mask, %vl, %sew
+//
+// %x = PseudoFOO_MASK ..., %allonesmask, %vl, %sew
 // ->
-// PseudoVMV_V_V %false, %true, %vl, %sew
+// %x = PseudoFOO ..., %vl, %sew
+//
+// %x = PseudoVMERGE_VVM %false, %false, %true, %allonesmask, %vl, %sew
+// ->
+// %x = PseudoVMV_V_V %false, %true, %vl, %sew
 //
 //===---------------------------------------------------------------------===//
 
 #include "RISCV.h"
+#include "RISCVISelDAGToDAG.h"
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wangpc-pp wrote:

Why do we need to include `RISCVISelDAGToDAG.h`?
And some other includes can be removed.

https://github.com/llvm/llvm-project/pull/71764