Re: [PATCH v1 8/8] target/riscv: Include RV32 instructions in RV64 build

[Richard Henderson <richard.henderson@linaro.org>]

On 4/2/21 1:03 PM, Alistair Francis wrote:
> Signed-off-by: Alistair Francis<alistair.francis@wdc.com>
> ---
>   target/riscv/insn16-32.decode | 24 ++++++++++++++++++++++++
>   target/riscv/insn16-64.decode | 31 +++++++++++++++++++++++++++++++
>   target/riscv/translate.c      | 18 +++++++++++++++++-
>   target/riscv/meson.build      |  7 +++++--
>   4 files changed, 77 insertions(+), 3 deletions(-)

Having these split out from the main decode file was a cool trick when we were 
sure that we never needed to support both.  Now, I think it would be better to 
merge the patterns back in to the main insn16.decode file.

You'd begin by adding a REQUIRE_64BIT(ctx) macro, much like the other REQUIRE 
macros in translate.c, using the translate-local is_32bit() function as 
discussed earlier.

You add this to all of the trans_* functions that are currently #ifdef 
TARGET_RISCV64, and merge the insn32-64.decode bits in first.

There may well be an issue of missing helper functions, particularly when it 
comes to RVF/RVD/RVV.  There's a suggestion that I made for Claudio for i386 
that may help here:

https://lists.gnu.org/archive/html/qemu-devel/2021-02/msg08595.html

where you add stubs that allow the gen_helper_foo() function to be declared, 
insist that it be optimized away, and reduce to an abort with -O0.

Only after insn32.decode is complete, do insn16.decode.  That's because many of 
the insns here will need the REQUIRE_64BIT in place for correctness.

E.g.

{
   ld          011  ... ... .. ... 00 @cl_d
   flw         011  ... ... .. ... 00 @cl_w
}

Since ld already has REQUIRE_64BIT, for is_32bit it returns false, and we fall 
into the flw code.

There will be one extra helper required, when the 64-bit RVC insn has a set of 
illegal operands:

static bool trans_c64_illegal(DisasContext *ctx, arg_empty *a)
{
     REQUIRE_64BIT(ctx);
     return trans_illegal(ctx, a);
}

for use with quadrant 1:

{
   c64_illegal 001 -  00000  ----- 01 # c.addiw, RES rd=0
   addiw       001 .  .....  ..... 01 @ci
   jal         001     ........... 01 @cj    rd=1  # C.JAL

}

and quadrant 2:

{
   c64_illegal 011 -  00000  ----- 10 # c.ldsp, RES rd=0
   ld          011 .  .....  ..... 10 @c_ldsp
   flw         011 .  .....  ..... 10 @c_lwsp
}


r~