target/arm: Convert Neon 3-reg-diff prewidening ops to decodetree

Convert the "pre-widening" insns VADDL, VSUBL, VADDW and VSUBW
in the Neon 3-registers-different-lengths group to decodetree.
These insns work by widening one or both inputs to double their
size, performing an add or subtract at the doubled size and
then storing the double-size result.

As usual, rather than copying the loop of the original decoder
(which needs awkward code to avoid problems when source and
destination registers overlap) we just unroll the two passes.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>

1 files changed, 43 insertions, 0 deletions

diff --git a/target/arm/neon-dp.decode b/target/arm/neon-dp.decode
index bd1b0e1..144a527 100644
--- a/target/arm/neon-dp.decode
+++ b/target/arm/neon-dp.decode
@@ -397,3 +397,46 @@ VCVT_FU_2sh      1111 001 1 1 . ...... .... 1111 0 . . 1 .... @2reg_vcvt
 # So we have a single decode line and check the cmode/op in the
 # trans function.
 Vimm_1r          1111 001 . 1 . 000 ... .... cmode:4 0 . op:1 1 .... @1reg_imm
+
+######################################################################
+# Within the "two registers, or three registers of different lengths"
+# grouping ([23,4]=0b10), bits [21:20] are either part of the opcode
+# decode: 0b11 for VEXT, two-reg-misc, VTBL, and duplicate-scalar;
+# or they are a size field for the three-reg-different-lengths and
+# two-reg-and-scalar insn groups (where size cannot be 0b11). This
+# is slightly awkward for decodetree: we handle it with this
+# non-exclusive group which contains within it two exclusive groups:
+# one for the size=0b11 patterns, and one for the size-not-0b11
+# patterns. This allows us to check that none of the insns within
+# each subgroup accidentally overlap each other. Note that all the
+# trans functions for the size-not-0b11 patterns must check and
+# return false for size==3.
+######################################################################
+{
+  # 0b11 subgroup will go here
+
+  # Subgroup for size != 0b11
+  [
+    ##################################################################
+    # 3-reg-different-length grouping:
+    # 1111 001 U 1 D sz!=11 Vn:4 Vd:4 opc:4 N 0 M 0 Vm:4
+    ##################################################################
+
+    &3diff vm vn vd size
+
+    @3diff       .... ... . . . size:2 .... .... .... . . . . .... \
+                 &3diff vm=%vm_dp vn=%vn_dp vd=%vd_dp
+
+    VADDL_S_3d   1111 001 0 1 . .. .... .... 0000 . 0 . 0 .... @3diff
+    VADDL_U_3d   1111 001 1 1 . .. .... .... 0000 . 0 . 0 .... @3diff
+
+    VADDW_S_3d   1111 001 0 1 . .. .... .... 0001 . 0 . 0 .... @3diff
+    VADDW_U_3d   1111 001 1 1 . .. .... .... 0001 . 0 . 0 .... @3diff
+
+    VSUBL_S_3d   1111 001 0 1 . .. .... .... 0010 . 0 . 0 .... @3diff
+    VSUBL_U_3d   1111 001 1 1 . .. .... .... 0010 . 0 . 0 .... @3diff
+
+    VSUBW_S_3d   1111 001 0 1 . .. .... .... 0011 . 0 . 0 .... @3diff
+    VSUBW_U_3d   1111 001 1 1 . .. .... .... 0011 . 0 . 0 .... @3diff
+  ]
+}