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

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>

1 files changed, 11 insertions, 1 deletions

diff --git a/target/hexagon/genptr.c b/target/hexagon/genptr.c
index be9c715ea8..ee0f86fab2 100644
--- a/target/hexagon/genptr.c
+++ b/target/hexagon/genptr.c
@@ -484,7 +484,17 @@ static void gen_write_new_pc_pcrel(DisasContext *ctx, int pc_off,
                                    TCGCond cond, TCGv pred)
 {
     target_ulong dest = ctx->pkt->pc + pc_off;
-    gen_write_new_pc_addr(ctx, tcg_constant_tl(dest), cond, pred);
+    if (ctx->pkt->pkt_has_multi_cof) {
+        gen_write_new_pc_addr(ctx, tcg_constant_tl(dest), cond, pred);
+    } else {
+        /* Defer this jump to the end of the TB */
+        ctx->branch_cond = TCG_COND_ALWAYS;
+        if (pred != NULL) {
+            ctx->branch_cond = cond;
+            tcg_gen_mov_tl(hex_branch_taken, pred);
+        }
+        ctx->branch_dest = dest;
+    }
 }
 
 static void gen_compare(TCGCond cond, TCGv res, TCGv arg1, TCGv arg2)