[SpecialCaseList] Filtering Globs with matching prefix

[vitalybuka]

This commit optimizes SpecialCaseList by using a RadixTree to filter
glob patterns based on their prefixes. When matching a query, the
RadixTree quickly identifies all glob patterns whose prefixes match
the query's prefix. This significantly reduces the number of glob
patterns that need to be fully evaluated, leading to performance
improvements, especially when dealing with a large number of patterns.

According to SpecialCaseListBM:

Lookup benchmarks (significant improvements):

OVERALL_GEOMEAN                       -0.8177

Lookup like prefix* benchmarks (huge improvements):

OVERALL_GEOMEAN                       -0.9819

https://gist.github.com/vitalybuka/824884bcbc1713e815068c279159dafe

[llvmbot]

@llvm/pr-subscribers-llvm-support

Author: Vitaly Buka (vitalybuka)

Changes

This commit optimizes SpecialCaseList by using a RadixTree to filter
glob patterns based on their prefixes. When matching a query, the
RadixTree quickly identifies all glob patterns whose prefixes match
the query's prefix. This significantly reduces the number of glob
patterns that need to be fully evaluated, leading to performance
improvements, especially when dealing with a large number of patterns.

---

Full diff: https://github.com/llvm/llvm-project/pull/164531.diff

2 Files Affected:

• (modified) llvm/include/llvm/Support/SpecialCaseList.h (+7)
• (modified) llvm/lib/Support/SpecialCaseList.cpp (+17-3)

diff --git a/llvm/include/llvm/Support/SpecialCaseList.h b/llvm/include/llvm/Support/SpecialCaseList.h
index ead765562504d..16f309329a0b5 100644
--- a/llvm/include/llvm/Support/SpecialCaseList.h
+++ b/llvm/include/llvm/Support/SpecialCaseList.h
@@ -13,10 +13,13 @@
 #define LLVM_SUPPORT_SPECIALCASELIST_H
 
 #include "llvm/ADT/ArrayRef.h"
+#include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/StringMap.h"
+#include "llvm/ADT/iterator_range.h"
 #include "llvm/Support/Allocator.h"
 #include "llvm/Support/Compiler.h"
 #include "llvm/Support/GlobPattern.h"
+#include "llvm/Support/RadixTree.h"
 #include "llvm/Support/Regex.h"
 #include <memory>
 #include <string>
@@ -162,6 +165,10 @@ class SpecialCaseList {
     };
 
     std::vector<GlobMatcher::Glob> Globs;
+
+    RadixTree<iterator_range<StringRef::const_iterator>,
+              SmallVector<const GlobMatcher::Glob *, 1>>
+        PrefixToGlob;
   };
 
   /// Represents a set of patterns and their line numbers
diff --git a/llvm/lib/Support/SpecialCaseList.cpp b/llvm/lib/Support/SpecialCaseList.cpp
index f74e52a3a7fa9..2a86cc37b6000 100644
--- a/llvm/lib/Support/SpecialCaseList.cpp
+++ b/llvm/lib/Support/SpecialCaseList.cpp
@@ -89,14 +89,28 @@ void SpecialCaseList::GlobMatcher::preprocess(bool BySize) {
       return A.Name.size() < B.Name.size();
     });
   }
+
+  for (auto &G : Globs) {
+    StringRef Prefix = G.Pattern.prefix();
+
+    auto &V = PrefixToGlob.emplace(Prefix).first->second;
+    V.emplace_back(&G);
+  }
 }
 
 void SpecialCaseList::GlobMatcher::match(
     StringRef Query,
     llvm::function_ref<void(StringRef Rule, unsigned LineNo)> Cb) const {
-  for (const auto &G : reverse(Globs))
-    if (G.Pattern.match(Query))
-      return Cb(G.Name, G.LineNo);
+  if (!PrefixToGlob.empty()) {
+    for (const auto &[_, V] : PrefixToGlob.find_prefixes(Query)) {
+      for (const auto *G : reverse(V)) {
+        if (G->Pattern.match(Query)) {
+          Cb(G->Name, G->LineNo);
+          break;
+        }
+      }
+    }
+  }
 }
 
 SpecialCaseList::Matcher::Matcher(bool UseGlobs, bool RemoveDotSlash)

[fmayer]

please add a comment to explain the reverse