Extend the existing conditional that generates INC/DEC, to also swap an
ADD for a SUB and vice versa when the immediate is 128. This facilitates
using OPC_ARITH_EvIb instead of OPC_ARITH_EvIz.
Best reviewed with "git diff -b".
Signed-off-by: Paolo Bonzini <pbonz...@redhat.com>
---
tcg/i386/tcg-target.c.inc | 40 +++++++++++++++++++++++----------------
1 file changed, 24 insertions(+), 16 deletions(-)
diff --git a/tcg/i386/tcg-target.c.inc b/tcg/i386/tcg-target.c.inc
index a83f8aab304..1791b959738 100644
--- a/tcg/i386/tcg-target.c.inc
+++ b/tcg/i386/tcg-target.c.inc
@@ -1316,23 +1316,31 @@ static void tgen_arithi(TCGContext *s, int c, int r0,
c &= 7;
}
- /* ??? While INC is 2 bytes shorter than ADDL $1, they also induce
- partial flags update stalls on Pentium4 and are not recommended
- by current Intel optimization manuals. */
- if (!cf && (c == ARITH_ADD || c == ARITH_SUB) && (val == 1 || val == -1)) {
- int is_inc = (c == ARITH_ADD) ^ (val < 0);
- if (TCG_TARGET_REG_BITS == 64) {
- /* The single-byte increment encodings are re-tasked as the
- REX prefixes. Use the MODRM encoding. */
- tcg_out_modrm(s, OPC_GRP5 + rexw,
- (is_inc ? EXT5_INC_Ev : EXT5_DEC_Ev), r0);
- } else {
- tcg_out8(s, (is_inc ? OPC_INC_r32 : OPC_DEC_r32) + r0);
+ if (!cf && (c == ARITH_ADD || c == ARITH_SUB)) {
+ /* ??? While INC is 2 bytes shorter than ADDL $1, they also induce
+ partial flags update stalls on Pentium4 and are not recommended
+ by current Intel optimization manuals. */
+ if (val == 1 || val == -1) {
+ int is_inc = (c == ARITH_ADD) ^ (val < 0);
+ if (TCG_TARGET_REG_BITS == 64) {
+ /* The single-byte increment encodings are re-tasked as the
+ REX prefixes. Use the MODRM encoding. */
+ tcg_out_modrm(s, OPC_GRP5 + rexw,
+ (is_inc ? EXT5_INC_Ev : EXT5_DEC_Ev), r0);
+ } else {
+ tcg_out8(s, (is_inc ? OPC_INC_r32 : OPC_DEC_r32) + r0);
+ }
+ return;
}
- return;
- }
-
- if (c == ARITH_AND) {
+ if (val == 128) {
+ /*
+ * Facilitate using an 8-bit immediate. Carry is inverted
+ * by this transformation, so do it only if cf == 0.
+ */
+ 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
