A.2.129.1 Values

The -xipo option can have the following values.

Defaults

If -xipo is not specified, -xipo=0 is assumed.

If only -xipo is specified, -xipo=1 is assumed.

Examples

The following example compiles and links in the same step.

example% CC -xipo -xO4 -o prog  part1.cc part2.cc part3.cc

The optimizer performs crossfile inlining across all three source files. This is done in the final link step, so the compilation of the source files need not all take place in a single compilation and could be over a number of separate compilations, each specifying the -xipo option.

The following example compiles and links in separate steps.

example% CC -xipo -xO4 -c part1.cc part2.cc
example% CC -xipo -xO4 -c part3.cc
example% CC -xipo -xO4 -o prog part1.o part2.o part3.o

The object files created in the compile steps have additional analysis information compiled within them to permit crossfile optimizations to take place at the link step.

Interactions

The -xipo option requires at least optimization level -xO4.

You cannot use both the -xipo option and the -xcrossfile option in the same compiler command line.

Warnings

When compiling and linking are performed in separate steps, -xipo must be specified in both steps to be effective.

Objects that are compiled without -xipo can be linked freely with objects that are compiled with -xipo.

Libraries do not participate in crossfile interprocedural analysis, even when they are compiled with -xipo, as shown in this example.

example% CC -xipo -xO4 one.cc two.cc three.cc
example% CC -xar -o mylib.a one.o two.o three.o
...
example% CC -xipo -xO4 -o myprog main.cc four.cc mylib.a

In this example, interprocedural optimizations will be performed between one.cc, two.cc and three.cc, and between main.cc and four.cc, but not between main.cc or four.cc and the routines in mylib.a. (The first compilation may generate warnings about undefined symbols, but the interprocedural optimizations will be performed because it is a compile and link step.)

The -xipo option generates significantly larger object files due to the additional information needed to perform optimizations across files. However, this additional information does not become part of the final executable binary file. Any increase in the size of the executable program will be due to the additional optimizations performed.