diff options
| author | Paolo Bonzini <pbonzini@redhat.com> | 2023-12-28 13:05:14 +0100 |
|---|---|---|
| committer | Richard Henderson <richard.henderson@linaro.org> | 2024-01-11 08:46:35 +1100 |
| commit | 64708db302edfe57474239a51d4dad4466fac44a (patch) | |
| tree | f4bf5355163a449b09e123d1b98302ab84c5dc67 /tcg | |
| parent | 34eac35f893664eb8545b98142e23d9954722766 (diff) | |
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>
Diffstat (limited to 'tcg')
| -rw-r--r-- | tcg/i386/tcg-target.c.inc | 49 |
1 files changed, 34 insertions, 15 deletions
diff --git a/tcg/i386/tcg-target.c.inc b/tcg/i386/tcg-target.c.inc index a83f8aab30..29e80af78b 100644 --- a/tcg/i386/tcg-target.c.inc +++ b/tcg/i386/tcg-target.c.inc @@ -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) { |