[binutils-gdb] x86: optimize XADD to ADD for same-register forms
Jan Beulich
jbeulich@sourceware.org
Fri Jun 19 07:49:31 GMT 2026
https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=6780979d416b57cdd6f6b8f55645f808b5a72fec
commit 6780979d416b57cdd6f6b8f55645f808b5a72fec
Author: Jan Beulich <jbeulich@suse.com>
Date: Fri Jun 19 09:47:42 2026 +0200
x86: optimize XADD to ADD for same-register forms
ADD requires less execution resources and is shorter to encode.
Diff:
---
gas/config/tc-i386.c | 11 +++++++++++
gas/testsuite/gas/i386/optimize-2.d | 3 +++
gas/testsuite/gas/i386/optimize-2.s | 4 ++++
gas/testsuite/gas/i386/optimize-2b.d | 3 +++
gas/testsuite/gas/i386/x86-64-optimize-3.d | 4 ++++
gas/testsuite/gas/i386/x86-64-optimize-3.s | 5 +++++
gas/testsuite/gas/i386/x86-64-optimize-3b.d | 4 ++++
opcodes/i386-opc.tbl | 2 +-
opcodes/i386-tbl.h | 2 +-
9 files changed, 36 insertions(+), 2 deletions(-)
diff --git a/gas/config/tc-i386.c b/gas/config/tc-i386.c
index d58c375c8d8..9b3f527d2c1 100644
--- a/gas/config/tc-i386.c
+++ b/gas/config/tc-i386.c
@@ -5187,6 +5187,17 @@ optimize_encoding (void)
i.tm.base_opcode = pp.dir_encoding == dir_encoding_load ? 0x8a : 0x88;
}
+ if (i.tm.mnem_off == MN_xadd
+ && i.reg_operands == 2
+ && i.op[0].regs == i.op[1].regs)
+ {
+ /* Optimize: -O:
+ xadd %rN, %rN -> add %rN, %rN
+ */
+ i.tm.opcode_space = SPACE_BASE;
+ i.tm.base_opcode = 0x00;
+ }
+
if (((i.tm.opcode_space == SPACE_0F
&& (i.tm.base_opcode | 1) == 0xbf
&& (i.types[0].bitfield.byte
diff --git a/gas/testsuite/gas/i386/optimize-2.d b/gas/testsuite/gas/i386/optimize-2.d
index 51f117966be..48703a86cba 100644
--- a/gas/testsuite/gas/i386/optimize-2.d
+++ b/gas/testsuite/gas/i386/optimize-2.d
@@ -48,6 +48,9 @@ Disassembly of section .text:
+[a-f0-9]+: 66 d1 e2 shl \$1,%dx
+[a-f0-9]+: d1 e2 shl \$1,%edx
+[a-f0-9]+: d1 e2 shl \$1,%edx
+ +[a-f0-9]+: 00 c9 add %cl,%cl
+ +[a-f0-9]+: 66 01 d2 add %dx,%dx
+ +[a-f0-9]+: 01 ff add %edi,%edi
+[a-f0-9]+: c5 f1 55 e9 vandnpd %xmm1,%xmm1,%xmm5
+[a-f0-9]+: c5 f9 6f d1 vmovdqa %xmm1,%xmm2
+[a-f0-9]+: c5 f9 6f d1 vmovdqa %xmm1,%xmm2
diff --git a/gas/testsuite/gas/i386/optimize-2.s b/gas/testsuite/gas/i386/optimize-2.s
index 102144592b1..68d9502dccb 100644
--- a/gas/testsuite/gas/i386/optimize-2.s
+++ b/gas/testsuite/gas/i386/optimize-2.s
@@ -59,6 +59,10 @@ _start:
sal $1, %edx
sal %edx
+ xadd %cl, %cl
+ xadd %dx, %dx
+ xadd %edi, %edi
+
vandnpd %zmm1, %zmm1, %zmm5
vmovdqa32 %xmm1, %xmm2
diff --git a/gas/testsuite/gas/i386/optimize-2b.d b/gas/testsuite/gas/i386/optimize-2b.d
index 359d4a097a0..5d270a07360 100644
--- a/gas/testsuite/gas/i386/optimize-2b.d
+++ b/gas/testsuite/gas/i386/optimize-2b.d
@@ -49,6 +49,9 @@ Disassembly of section .text:
+[a-f0-9]+: 66 01 d2 add %dx,%dx
+[a-f0-9]+: 01 d2 add %edx,%edx
+[a-f0-9]+: 01 d2 add %edx,%edx
+ +[a-f0-9]+: 00 c9 add %cl,%cl
+ +[a-f0-9]+: 66 01 d2 add %dx,%dx
+ +[a-f0-9]+: 01 ff add %edi,%edi
+[a-f0-9]+: c5 f1 55 e9 vandnpd %xmm1,%xmm1,%xmm5
+[a-f0-9]+: c5 f9 6f d1 vmovdqa %xmm1,%xmm2
+[a-f0-9]+: c5 f9 6f d1 vmovdqa %xmm1,%xmm2
diff --git a/gas/testsuite/gas/i386/x86-64-optimize-3.d b/gas/testsuite/gas/i386/x86-64-optimize-3.d
index 20d3d550041..0cc4ba8f450 100644
--- a/gas/testsuite/gas/i386/x86-64-optimize-3.d
+++ b/gas/testsuite/gas/i386/x86-64-optimize-3.d
@@ -94,6 +94,10 @@ Disassembly of section .text:
+[a-f0-9]+: 66 98 cbtw
+[a-f0-9]+: 98 cwtl
+[a-f0-9]+: 48 98 cltq
+ +[a-f0-9]+: d5 50 00 c9 add %r17b,%r17b
+ +[a-f0-9]+: 66 45 01 c0 add %r8w,%r8w
+ +[a-f0-9]+: 01 c0 add %eax,%eax
+ +[a-f0-9]+: 4d 01 ff add %r15,%r15
+[a-f0-9]+: c5 f1 55 e9 vandnpd %xmm1,%xmm1,%xmm5
+[a-f0-9]+: c5 f9 6f d1 vmovdqa %xmm1,%xmm2
+[a-f0-9]+: c5 f9 6f d1 vmovdqa %xmm1,%xmm2
diff --git a/gas/testsuite/gas/i386/x86-64-optimize-3.s b/gas/testsuite/gas/i386/x86-64-optimize-3.s
index 1b61d017e7b..010ccfbfb85 100644
--- a/gas/testsuite/gas/i386/x86-64-optimize-3.s
+++ b/gas/testsuite/gas/i386/x86-64-optimize-3.s
@@ -60,6 +60,11 @@ _start:
movsx rax, eax
.att_syntax prefix
+ xadd %r17b, %r17b
+ xadd %r8w, %r8w
+ xadd %eax, %eax
+ xadd %r15, %r15
+
vandnpd %zmm1, %zmm1, %zmm5
vmovdqa32 %xmm1, %xmm2
diff --git a/gas/testsuite/gas/i386/x86-64-optimize-3b.d b/gas/testsuite/gas/i386/x86-64-optimize-3b.d
index e7d211ed74c..ef6fd27c03c 100644
--- a/gas/testsuite/gas/i386/x86-64-optimize-3b.d
+++ b/gas/testsuite/gas/i386/x86-64-optimize-3b.d
@@ -95,6 +95,10 @@ Disassembly of section .text:
+[a-f0-9]+: 66 98 cbtw
+[a-f0-9]+: 98 cwtl
+[a-f0-9]+: 48 98 cltq
+ +[a-f0-9]+: d5 50 00 c9 add %r17b,%r17b
+ +[a-f0-9]+: 66 45 01 c0 add %r8w,%r8w
+ +[a-f0-9]+: 01 c0 add %eax,%eax
+ +[a-f0-9]+: 4d 01 ff add %r15,%r15
+[a-f0-9]+: c5 f1 55 e9 vandnpd %xmm1,%xmm1,%xmm5
+[a-f0-9]+: c5 f9 6f d1 vmovdqa %xmm1,%xmm2
+[a-f0-9]+: c5 f9 6f d1 vmovdqa %xmm1,%xmm2
diff --git a/opcodes/i386-opc.tbl b/opcodes/i386-opc.tbl
index bb547bd2ee7..63c3b5275b8 100644
--- a/opcodes/i386-opc.tbl
+++ b/opcodes/i386-opc.tbl
@@ -957,7 +957,7 @@ rex.wrxb, 0x4f, x64, NoSuf|IsPrefix, {}
// 486 extensions (BSWAP moved elsewhere).
-xadd, 0xfc0, i486, W|CheckOperandSize|Modrm|No_sSuf|HLEPrefixLock, { Reg8|Reg16|Reg32|Reg64, Reg8|Reg16|Reg32|Reg64|Unspecified|BaseIndex }
+xadd, 0xfc0, i486, W|CheckOperandSize|Modrm|No_sSuf|HLEPrefixLock|Optimize, { Reg8|Reg16|Reg32|Reg64, Reg8|Reg16|Reg32|Reg64|Unspecified|BaseIndex }
cmpxchg, 0xfb0, i486, W|CheckOperandSize|Modrm|No_sSuf|HLEPrefixLock, { Reg8|Reg16|Reg32|Reg64, Reg8|Reg16|Reg32|Reg64|Unspecified|BaseIndex }
invd, 0xf08, i486, NoSuf, {}
wbinvd, 0xf09, i486, NoSuf, {}
diff --git a/opcodes/i386-tbl.h b/opcodes/i386-tbl.h
index f1ecc6498af..e4738c32b06 100644
--- a/opcodes/i386-tbl.h
+++ b/opcodes/i386-tbl.h
@@ -8798,7 +8798,7 @@ static const insn_template i386_optab[] =
0, 0, 0, 0, 0, 0 } } } },
{ MN_xadd, 0xc0, 2, SPACE_0F, None,
{ 0, 1, 0, 1, 0, 0, 0, 1, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 6,
- 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0,
0, 0 },
{ { 4, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 } },
{ { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 } },
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