z/OS V1R13 XL C compiler introduces HOT (high-order loop analysis and transformation) and IPA (inter-procedural analysis) support for Metal C, thus improves optimization for Metal C programs. Specifying the HOT option or the IPA option with the METAL option enables the compiler to find more optimization opportunities to improve application performance.
The following example shows how to compile a Metal C program with HOT.
xlc -qmetal -qhot -S a.c
This command produces a.s.
The following example shows how to compile a Metal C program with IPA.
IPA compile phase:
xlc -qmetal -qipa -c x.c
xlc -qmetal -qipa -c y.c
These commands produce x.o and y.o.
IPA link phase:
xlc -qmetal -qipa -S x.o y.o
This command produces a.s.
You can find details about improved optimization for Metal C programs in Building Metal C programs with IPA in z/OS Metal C Programming Guide and Reference.