On Mon, 14 Nov 2022 16:46:37 PST (-0800), Kito Cheng wrote:
Hi Christoph:
This patch implements expansions for the cmpstrsi and the cmpstrnsi
builtins using Zbb instructions (if available).
This allows to inline calls to strcmp() and strncmp().
The expansion basically emits a peeled comparison sequence (i.e. a peeled
comparison loop) which compares XLEN bits per step if possible.
The emitted sequence can be controlled, by setting the maximum number
of compared bytes (-mstring-compare-inline-limit).
I would like to have a unified option interface,
maybe -m[no-]inline-str[n]cmp and -minline-str[n]cmp-limit.
And add some option like this:
-minline-str[n]cmp=[bitmanip|vector|auto] in future,
since I assume we'll have different versions of those things.
Can we just decide that from mtune? We'll probably have uarch-specific
string functions at some point, might as well start planning for it now.
gcc/ChangeLog:
* config/riscv/riscv-protos.h (riscv_expand_strn_compare): New
prototype.
* config/riscv/riscv-string.cc (GEN_EMIT_HELPER3): New helper
macros.
(GEN_EMIT_HELPER2): New helper macros.
(expand_strncmp_zbb_sequence): New function.
(riscv_emit_str_compare_zbb): New function.
(riscv_expand_strn_compare): New function.
* config/riscv/riscv.md (cmpstrnsi): Invoke expansion functions
for strn_compare.
(cmpstrsi): Invoke expansion functions for strn_compare.
* config/riscv/riscv.opt: Add new parameter
'-mstring-compare-inline-limit'.
We need to document this option.
