[PATCH 00/27] tcg: Simplify temporary usage

[Richard Henderson <richard.henderson@linaro.org>]

Based-on: 20230126043824.54819-1-richard.henderson@linaro.org
("[PATCH v5 00/36] tcg: Support for Int128 with helpers")

The biggest pitfall for new users of TCG is the fact that "normal"
temporaries die at branches, and we must therefore use a different
"local" temporary in that case.

The following patch set changes that, so that the "normal" temporary
is the one that lives across branches, and there is a special temporary
that dies at the end of the extended basic block, and this special
case is reserved for tcg internals.

TEMP_LOCAL is renamed TEMP_TB, which I believe to be more explicit and
less confusing.  TEMP_NORMAL is removed entirely.

I thought about putting in a proper full-power liveness analysis pass.
This would have eliminated the differences between all non-global
temporaries, and would have noticed when TEMP_LOCAL finally dies
within a translation and avoid any final writeback.
But I came to the conclusion that it was too expensive in runtime,
and so retaining some distinction in the types was required.

In addition, I found that the usage of temps within plugin-gen.c
(9 per guest memory operation) meant that we *must* have some form
of temp that can be re-used.  (There is one x86 instruction which
generates 62 memory operations; 62 * 9 == 558, which is larger than
our current TCG_MAX_TEMPS.)

However I did add a new liveness pass which, with a single pass over
the opcode stream, can see that a TEMP_LOCAL is only live within a
single extended basic block, and thus may be transformed to TEMP_EBB.

With this, and by not recycling TEMP_LOCAL, we can get identical code
out of the backend even when changing the front end translators are
adjusted to use TEMP_LOCAL for everything.

Benchmarking one test case, qemu-arm linux-test, the new liveness pass
comes in at about 1.6% on perf, but I can't see any difference in
wall clock time before and after the patch set.


r~


Richard Henderson (27):
  tcg: Adjust TCGContext.temps_in_use check
  accel/tcg: Pass max_insn to gen_intermediate_code by pointer
  accel/tcg: Use more accurate max_insns for tb_overflow
  tcg: Remove branch-to-next regardless of reference count
  tcg: Rename TEMP_LOCAL to TEMP_TB
  tcg: Add liveness_pass_0
  tcg: Remove TEMP_NORMAL
  tcg: Pass TCGTempKind to tcg_temp_new_internal
  tcg: Add tcg_temp_ebb_new_{i32,i64,ptr}
  tcg: Add tcg_gen_movi_ptr
  tcg: Use tcg_temp_ebb_new_* in tcg/
  accel/tcg/plugin: Use tcg_temp_ebb_*
  accel/tcg/plugin: Tidy plugin_gen_disable_mem_helpers
  tcg: Don't re-use TEMP_TB temporaries
  tcg: Change default temp lifetime to TEMP_TB
  target/arm: Drop copies in gen_sve_{ldr,str}
  target/arm: Don't use tcg_temp_local_new_*
  target/cris: Don't use tcg_temp_local_new
  target/hexagon: Don't use tcg_temp_local_new_*
  target/hppa: Don't use tcg_temp_local_new
  target/i386: Don't use tcg_temp_local_new
  target/mips: Don't use tcg_temp_local_new
  target/ppc: Don't use tcg_temp_local_new
  target/xtensa: Don't use tcg_temp_local_new_*
  exec/gen-icount: Don't use tcg_temp_local_new_i32
  tcg: Remove tcg_temp_local_new_*, tcg_const_local_*
  tcg: Update docs/devel/tcg-ops.rst for temporary changes

 docs/devel/tcg-ops.rst                      | 103 ++++----
 target/hexagon/idef-parser/README.rst       |   4 +-
 include/exec/gen-icount.h                   |   8 +-
 include/exec/translator.h                   |   4 +-
 include/tcg/tcg-op.h                        |   7 +-
 include/tcg/tcg.h                           |  64 ++---
 target/arm/translate-a64.h                  |   1 -
 target/hexagon/gen_tcg.h                    |   4 +-
 accel/tcg/plugin-gen.c                      |  33 +--
 accel/tcg/translate-all.c                   |   2 +-
 accel/tcg/translator.c                      |   6 +-
 target/alpha/translate.c                    |   2 +-
 target/arm/translate-a64.c                  |   6 -
 target/arm/translate-sve.c                  |  38 +--
 target/arm/translate.c                      |   8 +-
 target/avr/translate.c                      |   2 +-
 target/cris/translate.c                     |   8 +-
 target/hexagon/genptr.c                     |  16 +-
 target/hexagon/idef-parser/parser-helpers.c |   4 +-
 target/hexagon/translate.c                  |   4 +-
 target/hppa/translate.c                     |   5 +-
 target/i386/tcg/translate.c                 |  29 +--
 target/loongarch/translate.c                |   2 +-
 target/m68k/translate.c                     |   2 +-
 target/microblaze/translate.c               |   2 +-
 target/mips/tcg/translate.c                 |  59 ++---
 target/nios2/translate.c                    |   2 +-
 target/openrisc/translate.c                 |   2 +-
 target/ppc/translate.c                      |   8 +-
 target/riscv/translate.c                    |   2 +-
 target/rx/translate.c                       |   2 +-
 target/s390x/tcg/translate.c                |   2 +-
 target/sh4/translate.c                      |   2 +-
 target/sparc/translate.c                    |   2 +-
 target/tricore/translate.c                  |   2 +-
 target/xtensa/translate.c                   |  18 +-
 tcg/optimize.c                              |   2 +-
 tcg/tcg-op-gvec.c                           | 270 ++++++++++----------
 tcg/tcg-op.c                                | 258 +++++++++----------
 tcg/tcg.c                                   | 270 +++++++++++---------
 target/cris/translate_v10.c.inc             |  10 +-
 target/mips/tcg/nanomips_translate.c.inc    |   4 +-
 target/ppc/translate/spe-impl.c.inc         |   8 +-
 target/ppc/translate/vmx-impl.c.inc         |   4 +-
 target/hexagon/README                       |   8 +-
 target/hexagon/gen_tcg_funcs.py             |  18 +-
 46 files changed, 640 insertions(+), 677 deletions(-)

-- 
2.34.1