[performance] cache library performance enhancements (updates go-structr => v0.2.0) (#2575)

* update go-structr => v0.2.0

* update readme

* whoops, fix the link

vendor/github.com/zeebo/xxh3/accum_stubs_amd64.go

@@ -0,0 +1,40 @@
+package xxh3
+
+import (
+	"unsafe"
+
+	"github.com/klauspost/cpuid/v2"
+)
+
+var (
+	hasAVX2   = cpuid.CPU.Has(cpuid.AVX2)
+	hasSSE2   = cpuid.CPU.Has(cpuid.SSE2) // Always true on amd64
+	hasAVX512 = cpuid.CPU.Has(cpuid.AVX512F)
+)
+
+//go:noescape
+func accumAVX2(acc *[8]u64, data, key unsafe.Pointer, len u64)
+
+//go:noescape
+func accumAVX512(acc *[8]u64, data, key unsafe.Pointer, len u64)
+
+//go:noescape
+func accumSSE(acc *[8]u64, data, key unsafe.Pointer, len u64)
+
+//go:noescape
+func accumBlockAVX2(acc *[8]u64, data, key unsafe.Pointer)
+
+//go:noescape
+func accumBlockSSE(acc *[8]u64, data, key unsafe.Pointer)
+
+func withOverrides(avx512, avx2, sse2 bool, cb func()) {
+	avx512Orig, avx2Orig, sse2Orig := hasAVX512, hasAVX2, hasSSE2
+	hasAVX512, hasAVX2, hasSSE2 = avx512, avx2, sse2
+	defer func() { hasAVX512, hasAVX2, hasSSE2 = avx512Orig, avx2Orig, sse2Orig }()
+	cb()
+}
+
+func withAVX512(cb func())  { withOverrides(hasAVX512, false, false, cb) }
+func withAVX2(cb func())    { withOverrides(false, hasAVX2, false, cb) }
+func withSSE2(cb func())    { withOverrides(false, false, hasSSE2, cb) }
+func withGeneric(cb func()) { withOverrides(false, false, false, cb) }