--lto, --no_lto [ALPHA]

Enables link time optimization of LLVM bitcode files.

Caution

Link Time Optimization performs aggressive optimizations. Sometimes this can result in large chunks of code being removed.

Note

Although this option is fully supported in armlink, it is an [ALPHA] feature in ARM^® Compiler 6.
ARM Compiler does not support link time optimization on 32-bit Red Hat Enterprise Linux platforms.
Linux platforms are not supported when using ARM Compiler with the μVision^® IDE in the Keil MDK-ARM Microprocessor Development Kit.
Bitcode files are produced by armclang with the -flto option.

With the --no_lto option, armlink gives an error message if it encounters any bitcode files.

Default

The default is --no_lto.

Dependencies

Link time optimization requires the executable llvm-lto and the dependent library libLTO.

Table 11-4 Link time optimization dependencies

Dependency	Windows filename	Linux filename
`llvm-lto`	`llvm-lto.exe`	`llvm-lto`
`libLTO`	`LTO.dll`	`libLTO.so`

By default, the llvm-lto executable and dependent library libLTO are present in the same directory as armlink.

The search order for these dependencies is as follows.

On Windows:

llvm-lto.exe
1. The same directory as the armlink executable.
2. The directories in the current directory search path.
LTO.dll
1. The same directory as the armlink executable.
2. The directories in the current directory search path.

On Linux:

llvm-lto
1. The same directory as the armlink executable.
2. The directories in the current directory search path.
libLTO.so
1. The same directory as the armlink executable.
2. The directories in the D_LIBRARY_PATH environment variable.
3. The cache file /etc/ld.so.cache.
4. The directories /lib and /usr/lib.

Note

The armclang and llvm-lto executables and the libLTO library must come from the same ARM Compiler 6 installation. Any use of llvm-lto or libLTO other than those supplied with ARM Compiler 6 is unsupported.