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target/arm: Remove unnecessary gen_io_end() calls

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Since commit ba3e7926691ed3 it has been unnecessary for target code
to call gen_io_end() after an IO instruction in icount mode; it is
sufficient to call gen_io_start() before it and to force the end of
the TB.

Many now-unnecessary calls to gen_io_end() were removed in commit
9e9b10c6491153b, but some were missed or accidentally added later.
Remove unneeded calls from the arm target:

* the call in the handling of exception-return-via-LDM is
unnecessary, and the code is already forcing end-of-TB
* the call in the VFP access check code is more complicated:
we weren't ending the TB, so we need to add the code to
force that by setting DISAS_UPDATE
* the doc comment for ARM_CP_IO doesn't need to mention
gen_io_end() any more

Backports commit 55c812b74289863c348449135812027d188f040a from qemu
This commit is contained in:
Peter Maydell 2021-02-25 13:17:31 -05:00 committed by Lioncash
parent 083d207fb0
commit 167ed57625
2 changed files with 3 additions and 7 deletions
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7
qemu/target/arm/translate-vfp.inc.c
View file

@ -121,15 +121,14 @@ static bool full_vfp_access_check(DisasContext *s, bool ignore_vfp_enabled)
if (s->v7m_lspact) {
/*
* Lazy state saving affects external memory and also the NVIC,
* so we must mark it as an IO operation for icount.
* so we must mark it as an IO operation for icount (and cause
* this to be the last insn in the TB).
*/
if (tb_cflags(s->base.tb) & CF_USE_ICOUNT) {
s->base.is_jmp = DISAS_UPDATE;
gen_io_start(tcg_ctx);
}
gen_helper_v7m_preserve_fp_state(tcg_ctx, tcg_ctx->cpu_env);
if (tb_cflags(s->base.tb) & CF_USE_ICOUNT) {
gen_io_end(tcg_ctx);
}
/*
* If the preserve_fp_state helper doesn't throw an exception
* then it will clear LSPACT; we don't need to repeat this for

3
qemu/target/arm/translate.c
View file

@ -8044,9 +8044,6 @@ static bool do_ldm(DisasContext *s, arg_ldst_block *a, int min_n)
gen_io_start(tcg_ctx);
}
gen_helper_cpsr_write_eret(tcg_ctx, tcg_ctx->cpu_env, tmp);
if (tb_cflags(s->base.tb) & CF_USE_ICOUNT) {
gen_io_end(tcg_ctx);
}
tcg_temp_free_i32(tcg_ctx, tmp);
/* Must exit loop to check un-masked IRQs */
s->base.is_jmp = DISAS_EXIT;