Re: [PATCH 4/4] tcg/optimize: optimize TSTNE using smask and zmask
On 2/28/24 23:35, Paolo Bonzini wrote:
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;
+}
You need to care about type too -- for TCG_TYPE_I32, you'll want to OR in INT32_MIN. The
high bits of s_mask will be unknown (might be 1's from fold_masks, might be 0 from reset_ts).
But otherwise that's a good solution.
r~
Re: [PATCH 4/4] tcg/optimize: optimize TSTNE using smask and zmask
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 $0x8000, %rbx
test %ebx, %ebx
js y
and I get
brcond_i64 cc_dst,$0x8000,tstne,$L1
which works and matches your explanation:
i1.s_mask == 0x
i2.val == 0x8000
all_sign_bit_copies(i1) == 0x8000
u2.val & ~all_sign_bit_copies(i1) == 0
Thanks!
Paolo
Re: [PATCH 4/4] tcg/optimize: optimize TSTNE using smask and zmask
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.
r~
