Add tests for cases where we could fold a vmerge into its ops, but don't due to

it having an implicit merge operand.

Author: lukel97

llvm/test/CodeGen/RISCV/rvv/rvv-peephole-vmerge-vops.ll

@@ -1187,3 +1187,52 @@ define <vscale x 2 x i32> @vmerge_larger_vl_false_becomes_tail(<vscale x 2 x i32
   %b = call <vscale x 2 x i32> @llvm.riscv.vmerge.nxv2i32.nxv2i32(<vscale x 2 x i32> poison, <vscale x 2 x i32> %false, <vscale x 2 x i32> %a, <vscale x 2 x i1> %m, i64 3)
   ret <vscale x 2 x i32> %b
 }
+
+declare <vscale x 2 x i32> @llvm.riscv.vmacc.nxv2i32.nxv2i32(<vscale x 2 x i32>, <vscale x 2 x i32>, <vscale x 2 x i32>, i64, i64)
+
+; FIXME: We don't currently handle vmerge with an implicit passthru if the true
+; operand also has a tied dest. This could be folded into a masked vmacc with ta
+; policy.
+define <vscale x 2 x i32> @true_tied_dest_vmerge_implicit_passthru(<vscale x 2 x i32> %passthru, <vscale x 2 x i32> %x, <vscale x 2 x i32> %y, <vscale x 2 x i1> %m, i64 %avl) {
+; CHECK-LABEL: true_tied_dest_vmerge_implicit_passthru:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    vsetvli zero, a0, e32, m1, tu, ma
+; CHECK-NEXT:    vmv1r.v v11, v8
+; CHECK-NEXT:    vmacc.vv v11, v9, v10
+; CHECK-NEXT:    vsetvli zero, zero, e32, m1, ta, ma
+; CHECK-NEXT:    vmerge.vvm v8, v8, v11, v0
+; CHECK-NEXT:    ret
+  %a = call <vscale x 2 x i32> @llvm.riscv.vmacc.nxv2i32.nxv2i32(<vscale x 2 x i32> %passthru, <vscale x 2 x i32> %x, <vscale x 2 x i32> %y, i64 %avl, i64 0)
+  %b = call <vscale x 2 x i32> @llvm.riscv.vmerge.nxv2i32.nxv2i32(
+    <vscale x 2 x i32> poison,
+    <vscale x 2 x i32> %passthru,
+    <vscale x 2 x i32> %a,
+    <vscale x 2 x i1> %m,
+    i64 %avl
+  )
+  ret <vscale x 2 x i32> %b
+}
+
+declare <vscale x 2 x i32> @llvm.riscv.vadd.mask.nxv2i32.i32(<vscale x 2 x i32>, <vscale x 2 x i32>, i32, <vscale x 2 x i1>, i64, i64)
+
+; FIXME: We don't currently handle vmerge with an implicit passthru if the true
+; operand also has a tied dest, e.g. has a passthru since it's a masked
+; pseudo. This could be folded into a masked vadd with ta policy.
+define <vscale x 2 x i32> @true_mask_vmerge_implicit_passthru(<vscale x 2 x i32> %passthru, <vscale x 2 x i32> %x, <vscale x 2 x i32> %y, <vscale x 2 x i1> %m, i64 %avl) {
+; CHECK-LABEL: true_mask_vmerge_implicit_passthru:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    vsetvli zero, a0, e32, m1, tu, mu
+; CHECK-NEXT:    vmv1r.v v11, v8
+; CHECK-NEXT:    vadd.vv v11, v9, v10, v0.t
+; CHECK-NEXT:    vmv.v.v v8, v11
+; CHECK-NEXT:    ret
+  %a = call <vscale x 2 x i32> @llvm.riscv.vadd.mask.nxv2i32.nxv2i32(<vscale x 2 x i32> %passthru, <vscale x 2 x i32> %x, <vscale x 2 x i32> %y, <vscale x 2 x i1> %m, i64 %avl, i64 0)
+  %b = call <vscale x 2 x i32> @llvm.riscv.vmerge.nxv2i32.nxv2i32(
+    <vscale x 2 x i32> poison,
+    <vscale x 2 x i32> %passthru,
+    <vscale x 2 x i32> %a,
+    <vscale x 2 x i1> shufflevector(<vscale x 2 x i1> insertelement(<vscale x 2 x i1> poison, i1 true, i32 0), <vscale x 2 x i1> poison, <vscale x 2 x i32> zeroinitializer),
+    i64 %avl
+  )
+  ret <vscale x 2 x i32> %b
+}