On 8/11/23 03:45, Peter Maydell wrote:
On Fri, 11 Aug 2023 at 11:26, Peter Maydell <peter.mayd...@linaro.org> wrote:
On Tue, 8 Aug 2023 at 04:13, Richard Henderson
<richard.hender...@linaro.org> wrote:
Add the parameter to avoid TEST and pass along to tgen_arithi.
All current users pass false.
Signed-off-by: Richard Henderson <richard.hender...@linaro.org>
---
tcg/i386/tcg-target.c.inc | 16 ++++++++--------
1 file changed, 8 insertions(+), 8 deletions(-)
diff --git a/tcg/i386/tcg-target.c.inc b/tcg/i386/tcg-target.c.inc
index b88fc14afd..56549ff2a0 100644
--- a/tcg/i386/tcg-target.c.inc
+++ b/tcg/i386/tcg-target.c.inc
@@ -1418,15 +1418,15 @@ static void tcg_out_jxx(TCGContext *s, int opc,
TCGLabel *l, bool small)
}
}
-static void tcg_out_cmp(TCGContext *s, TCGArg arg1, TCGArg arg2,
- int const_arg2, int rexw)
+static void tcg_out_cmp(TCGContext *s, int rexw, TCGArg arg1, TCGArg arg2,
+ int const_arg2, bool cf)
{
if (const_arg2) {
- if (arg2 == 0) {
+ if (arg2 == 0 && !cf) {
/* test r, r */
tcg_out_modrm(s, OPC_TESTL + rexw, arg1, arg1);
} else {
- tgen_arithi(s, ARITH_CMP + rexw, arg1, arg2, 0);
+ tgen_arithi(s, ARITH_CMP + rexw, arg1, arg2, cf);
}
} else {
tgen_arithr(s, ARITH_CMP + rexw, arg1, arg2);
I don't really understand the motivation here.
Why are some uses of this function fine with using the TEST
insn, but some must avoid it? What does 'cf' stand for?
A comment would help here if there isn't a clearer argument
name available...
Looking at the following patch suggests perhaps:
/**
* tcg_out_cmp: Emit a compare, setting the X, Y, Z flags accordingly.
* @need_cf : true if the comparison must also set CF
*/
(fill in which XYZ flags you can rely on even if need_cf is false)
I can add that, yes.
Basically, test sets SZ flags, where cmp sets SZCO. I want to add an optimizaton using C,
so "cmp 0,x" should not be silently replaced by "test x,x".
r~
