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avoid repeated calls to cpuid, it is slow

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Brendan Hansknecht 2023-06-02 09:40:51 -07:00
parent 718b7f0ce2
commit 8eed06c3e1
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1 changed files with 37 additions and 14 deletions
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51
crates/compiler/builtins/bitcode/src/libc.zig
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@ -29,25 +29,48 @@ pub fn memcpy(noalias dest: [*]u8, noalias src: [*]const u8, len: usize) callcon
}
}
const MemcpyDecision = enum {
uninitialized,
folly_prefetchw,
folly_prefetcht0,
musl,
};
var memcpy_decision: MemcpyDecision = .uninitialized;
fn dispatch_memcpy(noalias dest: [*]u8, noalias src: [*]const u8, len: usize) callconv(.C) [*]u8 {
// TODO: Switch this to overwrite the memcpy_target pointer once the surgical linker can support it.
// Then dispatch will just happen on the first call instead of every call.
switch (arch) {
.x86_64 => {
if (cpuid.supports_avx2()) {
if (cpuid.supports_prefetchw()) {
// memcpy_target = folly.memcpy_prefetchw;
return folly.memcpy_prefetchw(dest, src, len);
} else {
// memcpy_target = folly.memcpy_prefetcht0;
return folly.memcpy_prefetcht0(dest, src, len);
}
} else {
// memcpy_target = musl.memcpy;
return musl.memcpy(dest, src, len);
// TODO: Switch this to overwrite the memcpy_target pointer once the surgical linker can support it.
// Then dispatch will just happen on the first call instead of every call.
// if (cpuid.supports_avx2()) {
// if (cpuid.supports_prefetchw()) {
// memcpy_target = folly.memcpy_prefetchw;
// } else {
// memcpy_target = folly.memcpy_prefetcht0;
// }
// } else {
// memcpy_target = musl.memcpy;
// }
// return memcpy_target(dest, src, len);
switch (memcpy_decision) {
.uninitialized => {
if (cpuid.supports_avx2()) {
if (cpuid.supports_prefetchw()) {
memcpy_decision = .folly_prefetchw;
} else {
memcpy_decision = .folly_prefetcht0;
}
} else {
memcpy_decision = .musl;
}
return dispatch_memcpy(dest, src, len);
},
.folly_prefetchw => return folly.memcpy_prefetchw(dest, src, len),
.folly_prefetcht0 => return folly.memcpy_prefetcht0(dest, src, len),
.musl => return musl.memcpy(dest, src, len),
}
},
else => unreachable,
}
// return memcpy_target(dest, src, len);
}