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This repository contains my work on a new ARM backend for the OCaml native code compiler, currently based on the 3.12.1 release. Compared to the old ARM backend, this one does the following:
- Support for both software and hardware floating-point using VFPv3-D16 or VFPv3(-D32).
- Properly supports interworking with Thumb/Thumb-2 code for both OCaml and C code.
- Supports dynamic linking and large memory models.
- Optional support for position-independent code via a command line option
-fPIC. This is disabled by default and not required for natdynlink.
- Can emit both ARM and Thumb-2 code, with avg. code size savings of 27% for Thumb-2 (quite close the optimal 30% advertised by ARM Ltd.).
- Supports both AAPCS (
armel) as well as extended VFP calling conventions (
- Supports several special ARM instructions to reduce code size and latency.
- Uses standard ARM EABI runtime functions instead of relying on GCC internals.
- Supports exception backtraces.
- Supports profiling using gprof.
Reported upstream as PR#5433.
You can specify the architecture when compiling with
ocamlopt using the
-farch command line option. Currently we support the following ARM architectures:
armv4for ARMv4 / ARMv4T / StrongARM (not supported for armhf)
armv5(not supported for armhf)
armv5te(not supported for armhf)
armv6(not supported for armhf)
armv6t2(not supported for armhf)
You can specify the floating-point unit when compiling with
ocamlopt using the
-ffpu command line option. Currently we support the following FPUs:
softfor software floating-point emulation (currently the only option for armel)
vfpv3-d16for VFPv3-D16 (armhf only)
vfpv3for VFPv3(-D32) (armhf only)
Performance / Code size savings
The new OCaml ARM backend (on armhf) is up to 4x faster in floating-point benchmarks compared to the 3.12.1 ARM backend (on armel), and code size is decreased by up to 28%. See the ocaml-arm 3.12.1+20111218 Benchmark for details.