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Hexagon (target/hexagon) Use direct block chaining for direct jump/branch

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Direct block chaining is documented here
https://qemu.readthedocs.io/en/latest/devel/tcg.html#direct-block-chaining

Recall that Hexagon allows packets with multiple jumps where only the
first one with a true predicate will actually jump.  We can  use
tcg_gen_goto_tb/tcg_gen_exit_tb when the packet contains a single
PC-relative branch or jump.  If not, we use tcg_gen_lookup_and_goto_ptr.

We add the following to DisasContext in order to delay the branching
until the end of packet commit (in gen_end_tb)
    branch_cond
        The TCGCond condition under which the branch is taken
        When branch_cond == TCG_COND_NEVER, there isn't a single
        direct branch in this packet.
        When branch_cond != TCG_COND_ALWAYS, the value is in
        hex_branch_taken
    branch_dest
        The destination of the branch

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Taylor Simpson <tsimpson@quicinc.com>
Message-Id: <20221108162906.3166-11-tsimpson@quicinc.com>
This commit is contained in:
Taylor Simpson 2022-11-08 08:29:05 -08:00
parent 97b16faf82
commit 1b9a7f2a13
3 changed files with 46 additions and 2 deletions
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34
target/hexagon/translate.c
View file

@ -116,10 +116,41 @@ static void gen_exec_counters(DisasContext *ctx)
hex_gpr[HEX_REG_QEMU_HVX_CNT], ctx->num_hvx_insns);
}
static bool use_goto_tb(DisasContext *ctx, target_ulong dest)
{
return translator_use_goto_tb(&ctx->base, dest);
}
static void gen_goto_tb(DisasContext *ctx, int idx, target_ulong dest)
{
if (use_goto_tb(ctx, dest)) {
tcg_gen_goto_tb(idx);
tcg_gen_movi_tl(hex_gpr[HEX_REG_PC], dest);
tcg_gen_exit_tb(ctx->base.tb, idx);
} else {
tcg_gen_movi_tl(hex_gpr[HEX_REG_PC], dest);
tcg_gen_lookup_and_goto_ptr();
}
}
static void gen_end_tb(DisasContext *ctx)
{
gen_exec_counters(ctx);
tcg_gen_exit_tb(NULL, 0);
if (ctx->branch_cond != TCG_COND_NEVER) {
if (ctx->branch_cond != TCG_COND_ALWAYS) {
TCGLabel *skip = gen_new_label();
tcg_gen_brcondi_tl(ctx->branch_cond, hex_branch_taken, 0, skip);
gen_goto_tb(ctx, 0, ctx->branch_dest);
gen_set_label(skip);
gen_goto_tb(ctx, 1, ctx->next_PC);
} else {
gen_goto_tb(ctx, 0, ctx->branch_dest);
}
} else {
tcg_gen_lookup_and_goto_ptr();
}
ctx->base.is_jmp = DISAS_NORETURN;
}
@ -807,6 +838,7 @@ static void hexagon_tr_init_disas_context(DisasContextBase *dcbase,
ctx->num_packets = 0;
ctx->num_insns = 0;
ctx->num_hvx_insns = 0;
ctx->branch_cond = TCG_COND_NEVER;
}
static void hexagon_tr_tb_start(DisasContextBase *db, CPUState *cpu)