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| author | Jan Beulich <jbeulich@suse.com> | 2019-07-01 08:35:08 +0200 |
|---|---|---|
| committer | Jan Beulich <jbeulich@suse.com> | 2019-07-01 08:35:08 +0200 |
| commit | 5641ec015a191e0584fd4cae57bb3262f7a51735 (patch) | |
| tree | 4a0364a281bb459f742a431a19448ef0e76d2083 /gas/doc | |
| parent | 79dec6b7baa243a4ada018a082491990adb6aec1 (diff) | |
| download | gdb-5641ec015a191e0584fd4cae57bb3262f7a51735.zip gdb-5641ec015a191e0584fd4cae57bb3262f7a51735.tar.gz gdb-5641ec015a191e0584fd4cae57bb3262f7a51735.tar.bz2 | |
x86: optimize AND/OR with twice the same register
It seems to be not uncommon for people to use AND or OR in this form for
just setting the status flags. TEST, which doesn't write to any
register other than EFLAGS, ought to be preferred. Make the change only
for -O2 and above though, at least for now.
Diffstat (limited to 'gas/doc')
| -rw-r--r-- | gas/doc/c-i386.texi | 3 |
1 files changed, 2 insertions, 1 deletions
diff --git a/gas/doc/c-i386.texi b/gas/doc/c-i386.texi index 2ceb594..e0d0bc9 100644 --- a/gas/doc/c-i386.texi +++ b/gas/doc/c-i386.texi @@ -477,7 +477,8 @@ instructions with 128-bit/256-bit VEX packed integer logical. EVEX vector register clearing instructions. In 64-bit mode VEX encoded instructions with commutative source operands will also have their source operands swapped if this allows using the 2-byte VEX prefix form -instead of the 3-byte one. +instead of the 3-byte one. Certain forms of AND as well as OR with the +same (register) operand specified twice will also be changed to TEST. @samp{-Os} includes @samp{-O2} optimization plus encodes 16-bit, 32-bit and 64-bit register tests with immediate as 8-bit register test with |