target/i386/tcg: do not compute all flags for SAHF

Only OF is needed, the others are overwritten.

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

target/i386/tcg/emit.c.inc

@@ -3778,7 +3778,7 @@ static void gen_SAHF(DisasContext *s, X86DecodedInsn *decode)
         return gen_illegal_opcode(s);
     }
     tcg_gen_shri_tl(s->T0, cpu_regs[R_EAX], 8);
-    gen_compute_eflags(s);
+    gen_neg_setcc(s, JCC_O << 1, cpu_cc_src);
     tcg_gen_andi_tl(cpu_cc_src, cpu_cc_src, CC_O);
     tcg_gen_andi_tl(s->T0, s->T0, CC_S | CC_Z | CC_A | CC_P | CC_C);
     tcg_gen_or_tl(cpu_cc_src, cpu_cc_src, s->T0);