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-rw-r--r--target/arm/neon-dp.decode17
1 files changed, 15 insertions, 2 deletions
diff --git a/target/arm/neon-dp.decode b/target/arm/neon-dp.decode
index ec3a92f..593f7ff 100644
--- a/target/arm/neon-dp.decode
+++ b/target/arm/neon-dp.decode
@@ -65,8 +65,21 @@ VCGT_U_3s 1111 001 1 0 . .. .... .... 0011 . . . 0 .... @3same
VCGE_S_3s 1111 001 0 0 . .. .... .... 0011 . . . 1 .... @3same
VCGE_U_3s 1111 001 1 0 . .. .... .... 0011 . . . 1 .... @3same
-VSHL_S_3s 1111 001 0 0 . .. .... .... 0100 . . . 0 .... @3same
-VSHL_U_3s 1111 001 1 0 . .. .... .... 0100 . . . 0 .... @3same
+# The _rev suffix indicates that Vn and Vm are reversed. This is
+# the case for shifts. In the Arm ARM these insns are documented
+# with the Vm and Vn fields in their usual places, but in the
+# assembly the operands are listed "backwards", ie in the order
+# Dd, Dm, Dn where other insns use Dd, Dn, Dm. For QEMU we choose
+# to consider Vm and Vn as being in different fields in the insn,
+# which allows us to avoid special-casing shifts in the trans_
+# function code. We would otherwise need to manually swap the operands
+# over to call Neon helper functions that are shared with AArch64,
+# which does not have this odd reversed-operand situation.
+@3same_rev .... ... . . . size:2 .... .... .... . q:1 . . .... \
+ &3same vn=%vm_dp vm=%vn_dp vd=%vd_dp
+
+VSHL_S_3s 1111 001 0 0 . .. .... .... 0100 . . . 0 .... @3same_rev
+VSHL_U_3s 1111 001 1 0 . .. .... .... 0100 . . . 0 .... @3same_rev
VMAX_S_3s 1111 001 0 0 . .. .... .... 0110 . . . 0 .... @3same
VMAX_U_3s 1111 001 1 0 . .. .... .... 0110 . . . 0 .... @3same