Hexagon (target/hexagon) Short-circuit packet register writes

In certain cases, we can avoid the overhead of writing to hex_new_value
and write directly to hex_gpr.  We add need_commit field to DisasContext
indicating if the end-of-packet commit is needed.  If it is not needed,
get_result_gpr() and get_result_gpr_pair() can return hex_gpr.

We pass the ctx->need_commit to helpers when needed.

Finally, we can early-exit from gen_reg_writes during packet commit.

There are a few instructions whose semantics write to the result before
reading all the inputs.  Therefore, the idef-parser generated code is
incompatible with short-circuit.  We tell idef-parser to skip them.

For debugging purposes, we add a cpu property to turn off short-circuit.
When the short-circuit property is false, we skip the analysis and force
the end-of-packet commit.

Here's a simple example of the TCG generated for
0x004000b4:  0x7800c020 {       R0 = #0x1 }

BEFORE:
 ---- 004000b4
 movi_i32 new_r0,$0x1
 mov_i32 r0,new_r0

AFTER:
 ---- 004000b4
 movi_i32 r0,$0x1

This patch reintroduces a use of check_for_attrib, so we remove the
G_GNUC_UNUSED added earlier in this series.

Signed-off-by: Taylor Simpson <tsimpson@quicinc.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Brian Cain <bcain@quicinc.com>
Message-Id: <20230427230012.3800327-12-tsimpson@quicinc.com>

1 files changed, 2 insertions, 1 deletions

diff --git a/target/hexagon/gen_tcg.h b/target/hexagon/gen_tcg.h
index 099a6cc..7e070c3 100644
--- a/target/hexagon/gen_tcg.h
+++ b/target/hexagon/gen_tcg.h
@@ -592,7 +592,8 @@
 #define fGEN_TCG_A5_ACS(SHORTCODE) \
     do { \
         gen_helper_vacsh_pred(PeV, cpu_env, RxxV, RssV, RttV); \
-        gen_helper_vacsh_val(RxxV, cpu_env, RxxV, RssV, RttV); \
+        gen_helper_vacsh_val(RxxV, cpu_env, RxxV, RssV, RttV, \
+                             tcg_constant_tl(ctx->need_commit)); \
     } while (0)
 
 #define fGEN_TCG_S2_cabacdecbin(SHORTCODE) \