target/i386: do not use gen_op_jz_ecx for repeated string operations

Explicitly generate a TSTEQ branch (which is optimized to NE x,0 if possible).
This does not make much sense yet, but later we will add more checks and some
will use a temporary to check on the decremented value of CX/ECX/RCX; it will
be clearer for all checks to share the same logic using TSTEQ(reg, cx_mask).

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Link: https://lore.kernel.org/r/20241215090613.89588-10-pbonzini@redhat.com
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/target/i386/tcg/translate.c b/target/i386/tcg/translate.c
index 8bc91c3de31255e18bfc760a5dce01cd7de3c7e4..7a3caf8b9964578730f258e87fb2be69c89bc56b 100644 (file)
--- a/target/i386/tcg/translate.c
+++ b/target/i386/tcg/translate.c
@@ -1338,6 +1338,7 @@ static void do_gen_rep(DisasContext *s, MemOp ot,
                        bool is_repz_nz)
 {
     TCGLabel *done = gen_new_label();
+    target_ulong cx_mask = MAKE_64BIT_MASK(0, 8 << s->aflag);
     bool had_rf = s->flags & HF_RF_MASK;
 
     /*
@@ -1360,7 +1361,7 @@ static void do_gen_rep(DisasContext *s, MemOp ot,
     tcg_set_insn_start_param(s->base.insn_start, 1, CC_OP_DYNAMIC);
 
     /* Any iteration at all?  */
-    gen_op_jz_ecx(s, done);
+    tcg_gen_brcondi_tl(TCG_COND_TSTEQ, cpu_regs[R_ECX], cx_mask, done);
 
     fn(s, ot);
     gen_op_add_reg_im(s, s->aflag, R_ECX, -1);