RE: [PATCH v4 09/12] target/hexagon: import lexer for idef-parser

[Taylor Simpson]

>From: Paolo Montesel <paolo.montesel.revng@gmail.com> 
>Sent: Wednesday, April 28, 2021 5:25 AM
>To: Taylor Simpson <tsimpson@quicinc.com>
>Cc: Alessandro Di Federico <ale.qemu@rev.ng>; qemu-devel@nongnu.org; Brian 
>Cain <bcain@quicinc.com>; nizzo@rev.ng; >philmd@redhat.com; 
>richard.henderson@linaro.org; Alessandro Di Federico <ale@rev.ng>
>Subject: Re: [PATCH v4 09/12] target/hexagon: import lexer for idef-parser
>
>Thanks for spotting this. It's actually a bug in the lexer. The token 
>`{IMM_ID}"iV"` didn't initialize `bit_width`. Now it does. This is the >result:
>
>void emit_J2_jump(DisasContext *ctx, Insn *insn, Packet *pkt, int riV)
>/* fIMMEXT(riV); (riV = riV & ~3); (PC = fREAD_PC()+riV);} */
>{
>int64_t qemu_tmp_0 = ~((int64_t)3ULL);
>int32_t qemu_tmp_1 = riV & qemu_tmp_0;
>riV = qemu_tmp_1;
>TCGv_i32 tmp_0 = tcg_temp_local_new_i32();
>tcg_gen_movi_i32(tmp_0, ctx->base.pc_next);
>TCGv_i32 tmp_1 = tcg_temp_local_new_i32();
>tcg_gen_addi_i32(tmp_1, tmp_0, (int64_t)riV);
>tcg_temp_free_i32(tmp_0);
>gen_write_new_pc(tmp_1);
>tcg_temp_free_i32(tmp_1);
>}
>
>The `(int64_t)riV` cast is actually useless so I simply dropped it, thanks for 
>pointing it out.
>
>This is all gonna be in the next patchset ofc.
>
>~Paolo

This could be further simplified by doing the add in the parser and generating
    TCGv tmp_1 = tcg_const_tl(ctx->base.pc_next + riV);
Have you looked at the host code that is generated?  I would expect it to do 
the constant folding, so the executed code is OK.  However, there's extra time 
spent building up TCG that could be avoided.


Taylor