Sometimes bpf developer might want to develop different codes
based on particular cpu versioins. For example, cpu v1/v2/v3
branch target is 16bit while cpu v4 branch target is 32bit,
thus cpu v4 allows more aggressive loop unrolling than cpu v1/v2/v3
(see [1] for a kernel selftest failure due to this).
We would like to maintain aggressive loop unrolling for cpu v4
while limit loop unrolling for earlier cpu versions.
Another example, signed divide also only available with cpu v4.
Actually, adding cpu specific macros are fairly common
in llvm. For example, x86 has maco like 'i486', '__pentium_mmx__', etc.
AArch64 has '__ARM_NEON', '__ARM_FEATURE_SVE', etc.
This patch added __BPF_CPU_VERSION__ macro. Current possible values
are 0/1/2/3/4. The following are the -mcpu=... to __BPF_CPU_VERSION__
mapping:
```
cpu __BPF_CPU_VERSION__
no -mcpu=<...> 1
-mcpu=v1 1
-mcpu=v2 2
-mcpu=v3 3
-mcpu=v4 4
-mcpu=generic 1
-mcpu=probe 0
```
This patch also added some macros for developers to identify some cpu
insn features:
```
feature macro enabled in which cpu
__BPF_FEATURE_JMP_EXT >= v2
__BPF_FEATURE_JMP32 >= v3
__BPF_FEATURE_ALU32 >= v3
__BPF_FEATURE_LDSX >= v4
__BPF_FEATURE_MOVSX >= v4
__BPF_FEATURE_BSWAP >= v4
__BPF_FEATURE_SDIV_SMOD >= v4
__BPF_FEATURE_GOTOL >= v4
__BPF_FEATURE_ST >= v4
```
[1]
https://lore.kernel.org/bpf/3e3a8a30-dde0-43a1-981e-2274962780ef@linux.dev/
"DefineStd(Builder, "bpf", Opts)" generates the following three
macros:
bpf
__bpf
__bpf__
and the macro "bpf" is due to the fact that the target language
is C which allows GNU extensions.
The name "bpf" could be easily used as variable name or type
field name. For example, in current linux kernel, there are
four places where bpf is used as a field name. If the corresponding
types are included in bpf program, the compilation error will
occur.
This patch removed predefined macro "bpf" as well as "__bpf" which
is rarely used if used at all.
Signed-off-by: Yonghong Song <yhs@fb.com>
Differential Revision: https://reviews.llvm.org/D61173
llvm-svn: 359310
