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

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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>
This commit is contained in:
Taylor Simpson 2023-04-27 16:00:02 -07:00
parent b9f0326bf7
commit d54c56156f
16 changed files with 128 additions and 30 deletions
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10
target/hexagon/gen_helper_protos.py
View file

@ -86,6 +86,8 @@ def gen_helper_prototype(f, tag, tagregs, tagimms):
def_helper_size = len(regs) + len(imms) + numscalarreadwrite + 1
if hex_common.need_pkt_has_multi_cof(tag):
def_helper_size += 1
if hex_common.need_pkt_need_commit(tag):
def_helper_size += 1
if hex_common.need_part1(tag):
def_helper_size += 1
if hex_common.need_slot(tag):
@ -103,6 +105,8 @@ def gen_helper_prototype(f, tag, tagregs, tagimms):
def_helper_size = len(regs) + len(imms) + numscalarreadwrite
if hex_common.need_pkt_has_multi_cof(tag):
def_helper_size += 1
if hex_common.need_pkt_need_commit(tag):
def_helper_size += 1
if hex_common.need_part1(tag):
def_helper_size += 1
if hex_common.need_slot(tag):
@ -156,10 +160,12 @@ def gen_helper_prototype(f, tag, tagregs, tagimms):
for immlett, bits, immshift in imms:
f.write(", s32")
## Add the arguments for the instruction pkt_has_multi_cof, slot and
## part1 (if needed)
## Add the arguments for the instruction pkt_has_multi_cof,
## pkt_needs_commit, PC, next_PC, slot, and part1 (if needed)
if hex_common.need_pkt_has_multi_cof(tag):
f.write(", i32")
if hex_common.need_pkt_need_commit(tag):
f.write(', i32')
if hex_common.need_PC(tag):
f.write(", i32")
if hex_common.helper_needs_next_PC(tag):