* [PATCH] tcg/i386: convert add/sub of 128 to sub/add of -128
@ 2023-12-21 13:43 Paolo Bonzini
2023-12-27 20:13 ` Richard Henderson
0 siblings, 1 reply; 2+ messages in thread
From: Paolo Bonzini @ 2023-12-21 13:43 UTC (permalink / raw)
To: qemu-devel; +Cc: richard.henderson
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
tcg/i386/tcg-target.c.inc | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)
diff --git a/tcg/i386/tcg-target.c.inc b/tcg/i386/tcg-target.c.inc
index a83f8aab304..4e9f372d4fd 100644
--- a/tcg/i386/tcg-target.c.inc
+++ b/tcg/i386/tcg-target.c.inc
@@ -1332,7 +1332,11 @@ static void tgen_arithi(TCGContext *s, int c, int r0,
return;
}
- if (c == ARITH_AND) {
+ if ((c == ARITH_ADD || c == ARITH_SUB) && val == 128) {
+ /* Facilitate using an 8-bit immediate. */
+ c ^= ARITH_ADD ^ ARITH_SUB;
+ val = -128;
+ } else if (c == ARITH_AND) {
if (TCG_TARGET_REG_BITS == 64) {
if (val == 0xffffffffu) {
tcg_out_ext32u(s, r0, r0);
--
2.43.0
^ permalink raw reply related [flat|nested] 2+ messages in thread* Re: [PATCH] tcg/i386: convert add/sub of 128 to sub/add of -128
2023-12-21 13:43 [PATCH] tcg/i386: convert add/sub of 128 to sub/add of -128 Paolo Bonzini
@ 2023-12-27 20:13 ` Richard Henderson
0 siblings, 0 replies; 2+ messages in thread
From: Richard Henderson @ 2023-12-27 20:13 UTC (permalink / raw)
To: Paolo Bonzini, qemu-devel
On 12/22/23 00:43, Paolo Bonzini wrote:
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
> tcg/i386/tcg-target.c.inc | 6 +++++-
> 1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/tcg/i386/tcg-target.c.inc b/tcg/i386/tcg-target.c.inc
> index a83f8aab304..4e9f372d4fd 100644
> --- a/tcg/i386/tcg-target.c.inc
> +++ b/tcg/i386/tcg-target.c.inc
> @@ -1332,7 +1332,11 @@ static void tgen_arithi(TCGContext *s, int c, int r0,
> return;
> }
>
> - if (c == ARITH_AND) {
> + if ((c == ARITH_ADD || c == ARITH_SUB) && val == 128) {
> + /* Facilitate using an 8-bit immediate. */
> + c ^= ARITH_ADD ^ ARITH_SUB;
> + val = -128;
> + } else if (c == ARITH_AND) {
> if (TCG_TARGET_REG_BITS == 64) {
> if (val == 0xffffffffu) {
> tcg_out_ext32u(s, r0, r0);
Need to check for !cf, because this swaps the sense of carry.
Ought to merge this with the inc/dec block above to save comparisons.
r~
^ permalink raw reply [flat|nested] 2+ messages in thread
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2023-12-21 13:43 [PATCH] tcg/i386: convert add/sub of 128 to sub/add of -128 Paolo Bonzini
2023-12-27 20:13 ` Richard Henderson
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