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tcg/i386: convert add/sub of 128 to sub/add of -128 

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.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20231228120514.70205-1-pbonzini@redhat.com>
[rth: Use a switch on C]
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
This commit is contained in:
Paolo Bonzini 2023-12-28 13:05:14 +01:00 committed by Richard Henderson
parent 34eac35f89
commit 64708db302
1 changed files with 34 additions and 15 deletions

49
tcg/i386/tcg-target.c.inc
View File

@ -1316,23 +1316,41 @@ 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);
switch (c) {
case ARITH_ADD:
case ARITH_SUB:
if (!cf) {
/*
* ??? 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;
}
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;
}
}
return;
}
break;
if (c == ARITH_AND) {
case ARITH_AND:
if (TCG_TARGET_REG_BITS == 64) {
if (val == 0xffffffffu) {
tcg_out_ext32u(s, r0, r0);
@ -1351,6 +1369,7 @@ static void tgen_arithi(TCGContext *s, int c, int r0,
tcg_out_ext16u(s, r0, r0);
return;
}
break;
}
if (val == (int8_t)val) {