```On 2/29/24 00:10, Richard Henderson wrote:
```
```On 2/28/24 01:11, Paolo Bonzini wrote:
```
```-    /* TSTNE x,sign -> LT x,0 */
-    if (arg_is_const_val(*p2, (ctx->type == TCG_TYPE_I32
-                               ? INT32_MIN : INT64_MIN))) {
+    /* TSTNE x,i -> LT x,0 if i only includes sign bit copies */
+    if (arg_is_const(*p2) && (arg_info(*p2)->val & ~i1->s_mask) == 0) {
```
```
```
This is a good idea, but s_mask isn't defined like you think -- it is *repetitions* of the sign bit, but not including the sign bit itself. For INT64_MIN, s_mask == 0.
```
So for TSTNE min,min, (min & ~0) != 0, so the test won't pass.
```
```
Oh! So I have to squash:

diff --git a/tcg/optimize.c b/tcg/optimize.c
index ab976a5bbe7..44d1b1a6d8a 100644
--- a/tcg/optimize.c
+++ b/tcg/optimize.c
@@ -140,6 +140,12 @@ static inline bool arg_is_const_val(TCGArg arg, uint64_t
val)
return ts_is_const_val(arg_temp(arg), val);
}
```
+/* Calculate all the copies of the sign bit, both redundant and not. */
```+static inline uint64_t all_sign_bit_copies(TempOptInfo *info)
+{
+    return (info->s_mask >> 1) | INT64_MIN;
+}
+
static inline bool ts_is_copy(TCGTemp *ts)
{
return ts_info(ts)->next_copy != ts;
@@ -825,7 +831,7 @@ static int do_constant_folding_cond1(OptContext *ctx, TCGOp
*op, TCGArg dest,
}
```
/* TSTNE x,i -> LT x,0 if i only includes sign bit copies */
```-    if (arg_is_const(*p2) && (arg_info(*p2)->val & ~i1->s_mask) == 0) {
+    if (arg_is_const(*p2) && (arg_info(*p2)->val & ~all_sign_bit_copies(i1))
== 0) {
*p2 = arg_new_constant(ctx, 0);
*pcond = tcg_tst_ltge_cond(cond);
return -1;

I tested with

movq \$0xffffffff80000000, %rbx
test %ebx, %ebx
js y

and I get

brcond_i64 cc_dst,\$0x80000000,tstne,\$L1

which works and matches your explanation: