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target/i386: cleanup cc_op changes for REP/REPZ/REPNZ

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gen_update_cc_op must be called before control flow splits.  Do it
where the jump on ECX!=0 is translated.

On the other hand, remove the call before gen_jcc1, which takes care of
it already, and explain why REPZ/REPNZ need not use CC_OP_DYNAMIC---the
translation block ends before any control-flow-dependent cc_op could
be observed.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Paolo Bonzini 2024-04-10 12:29:52 +02:00
parent 64ddadc6bb
commit bbba9594e8
1 changed files with 10 additions and 4 deletions
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14
target/i386/tcg/translate.c
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@ -1242,11 +1242,15 @@ static inline void gen_jcc1(DisasContext *s, int b, TCGLabel *l1)
}
/* XXX: does not work with gdbstub "ice" single step - not a
serious problem */
serious problem. The caller can jump to the returned label
to stop the REP but, if the flags have changed, it has to call
gen_update_cc_op before doing so. */
static TCGLabel *gen_jz_ecx_string(DisasContext *s)
{
TCGLabel *l1 = gen_new_label();
TCGLabel *l2 = gen_new_label();
gen_update_cc_op(s);
gen_op_jnz_ecx(s, l1);
gen_set_label(l2);
gen_jmp_rel_csize(s, 0, 1);
@ -1342,7 +1346,6 @@ static void gen_repz(DisasContext *s, MemOp ot,
void (*fn)(DisasContext *s, MemOp ot))
{
TCGLabel *l2;
gen_update_cc_op(s);
l2 = gen_jz_ecx_string(s);
fn(s, ot);
gen_op_add_reg_im(s, s->aflag, R_ECX, -1);
@ -1364,15 +1367,18 @@ static void gen_repz2(DisasContext *s, MemOp ot, int nz,
void (*fn)(DisasContext *s, MemOp ot))
{
TCGLabel *l2;
gen_update_cc_op(s);
l2 = gen_jz_ecx_string(s);
fn(s, ot);
gen_op_add_reg_im(s, s->aflag, R_ECX, -1);
gen_update_cc_op(s);
gen_jcc1(s, (JCC_Z << 1) | (nz ^ 1), l2);
if (s->repz_opt) {
gen_op_jz_ecx(s, l2);
}
/*
* Only one iteration is done at a time, so the translation
* block ends unconditionally after this instruction and there
* is no control flow junction - no need to set CC_OP_DYNAMIC.
*/
gen_jmp_rel_csize(s, -cur_insn_len(s), 0);
}