diff --git a/src/main/java/com/google/devtools/build/lib/actions/Artifact.java b/src/main/java/com/google/devtools/build/lib/actions/Artifact.java
index 72d2637..eb9165a 100644
--- a/src/main/java/com/google/devtools/build/lib/actions/Artifact.java
+++ b/src/main/java/com/google/devtools/build/lib/actions/Artifact.java
@@ -200,7 +200,7 @@
       throw new IllegalArgumentException(execPath + ": illegal execPath for " + path
           + " (root: " + root + ")");
     }
-    if (execPath.segmentCount() == 0) {
+    if (execPath.isEmpty()) {
       throw new IllegalArgumentException(
           "it is illegal to create an artifact with an empty execPath");
     }
diff --git a/src/main/java/com/google/devtools/build/lib/actions/ArtifactFactory.java b/src/main/java/com/google/devtools/build/lib/actions/ArtifactFactory.java
index 1aba67c..7382944 100644
--- a/src/main/java/com/google/devtools/build/lib/actions/ArtifactFactory.java
+++ b/src/main/java/com/google/devtools/build/lib/actions/ArtifactFactory.java
@@ -298,7 +298,7 @@
         baseExecPath,
         baseRoot);
     Preconditions.checkState(
-        relativePath.segmentCount() > 0, "%s %s %s", relativePath, baseExecPath, baseRoot);
+        !relativePath.isEmpty(), "%s %s %s", relativePath, baseExecPath, baseRoot);
     PathFragment execPath =
         baseExecPath == null ? relativePath : baseExecPath.getRelative(relativePath);
     execPath = execPath.normalize();
diff --git a/src/main/java/com/google/devtools/build/lib/actions/ArtifactRoot.java b/src/main/java/com/google/devtools/build/lib/actions/ArtifactRoot.java
index 71449aa..3363dc3 100644
--- a/src/main/java/com/google/devtools/build/lib/actions/ArtifactRoot.java
+++ b/src/main/java/com/google/devtools/build/lib/actions/ArtifactRoot.java
@@ -61,7 +61,8 @@
       return asSourceRoot(packageRoot);
     } else {
       Path actualRootPath = packageRoot.asPath();
-      for (int i = 0; i < repository.getSourceRoot().segmentCount(); i++) {
+      int segmentCount = repository.getSourceRoot().segmentCount();
+      for (int i = 0; i < segmentCount; i++) {
         actualRootPath = actualRootPath.getParentDirectory();
       }
       return asSourceRoot(Root.fromPath(actualRootPath));
diff --git a/src/main/java/com/google/devtools/build/lib/actions/FilesetTraversalParamsFactory.java b/src/main/java/com/google/devtools/build/lib/actions/FilesetTraversalParamsFactory.java
index 544f09f..89fc76b 100644
--- a/src/main/java/com/google/devtools/build/lib/actions/FilesetTraversalParamsFactory.java
+++ b/src/main/java/com/google/devtools/build/lib/actions/FilesetTraversalParamsFactory.java
@@ -123,9 +123,7 @@
       ImmutableList<FilesetTraversalParams> nested,
       PathFragment destDir,
       @Nullable Set<String> excludes) {
-    if (nested.size() == 1
-        && destDir.segmentCount() == 0
-        && (excludes == null || excludes.isEmpty())) {
+    if (nested.size() == 1 && destDir.isEmpty() && (excludes == null || excludes.isEmpty())) {
       // Wrapping the traversal here would not lead to a different result: the output location is
       // the same and there are no additional excludes.
       return Iterables.getOnlyElement(nested);
diff --git a/src/main/java/com/google/devtools/build/lib/bazel/rules/java/BazelJavaSemantics.java b/src/main/java/com/google/devtools/build/lib/bazel/rules/java/BazelJavaSemantics.java
index cc28554..b50259e 100644
--- a/src/main/java/com/google/devtools/build/lib/bazel/rules/java/BazelJavaSemantics.java
+++ b/src/main/java/com/google/devtools/build/lib/bazel/rules/java/BazelJavaSemantics.java
@@ -794,9 +794,10 @@
   @Override
   public PathFragment getDefaultJavaResourcePath(PathFragment path) {
     // Look for src/.../resources to match Maven repository structure.
-    for (int i = 0; i < path.segmentCount() - 2; ++i) {
-      if (path.getSegment(i).equals("src") && path.getSegment(i + 2).equals("resources")) {
-        return path.subFragment(i + 3, path.segmentCount());
+    List<String> segments = path.getSegments();
+    for (int i = 0; i < segments.size() - 2; ++i) {
+      if (segments.get(i).equals("src") && segments.get(i + 2).equals("resources")) {
+        return path.subFragment(i + 3);
       }
     }
     PathFragment javaPath = JavaUtil.getJavaPath(path);
diff --git a/src/main/java/com/google/devtools/build/lib/buildtool/SymlinkForest.java b/src/main/java/com/google/devtools/build/lib/buildtool/SymlinkForest.java
index 13b57cf..4ed8fda 100644
--- a/src/main/java/com/google/devtools/build/lib/buildtool/SymlinkForest.java
+++ b/src/main/java/com/google/devtools/build/lib/buildtool/SymlinkForest.java
@@ -123,7 +123,8 @@
         continue;
       }
       Root pkgRoot = entry.getValue();
-      for (int i = 1; i <= pkgId.getPackageFragment().segmentCount(); i++) {
+      int segmentCount = pkgId.getPackageFragment().segmentCount();
+      for (int i = 1; i <= segmentCount; i++) {
         PackageIdentifier dir = createInRepo(pkgId, pkgId.getPackageFragment().subFragment(0, i));
         Set<Root> roots = dirRootsMap.computeIfAbsent(dir, k -> Sets.newHashSet());
         roots.add(pkgRoot);
diff --git a/src/main/java/com/google/devtools/build/lib/cmdline/PackageIdentifier.java b/src/main/java/com/google/devtools/build/lib/cmdline/PackageIdentifier.java
index 9469ddd..ac62a3a 100644
--- a/src/main/java/com/google/devtools/build/lib/cmdline/PackageIdentifier.java
+++ b/src/main/java/com/google/devtools/build/lib/cmdline/PackageIdentifier.java
@@ -86,10 +86,10 @@
     if (tofind.startsWith(Label.EXTERNAL_PATH_PREFIX)) {
       // TODO(ulfjack): Remove this when kchodorow@'s exec root rearrangement has been rolled out.
       RepositoryName repository = RepositoryName.create("@" + tofind.getSegment(1));
-      return PackageIdentifier.create(repository, tofind.subFragment(2, tofind.segmentCount()));
+      return PackageIdentifier.create(repository, tofind.subFragment(2));
     } else if (!tofind.normalize().isNormalized()) {
       RepositoryName repository = RepositoryName.create("@" + tofind.getSegment(1));
-      return PackageIdentifier.create(repository, tofind.subFragment(2, tofind.segmentCount()));
+      return PackageIdentifier.create(repository, tofind.subFragment(2));
     } else {
       return PackageIdentifier.createInMainRepo(tofind);
     }
diff --git a/src/main/java/com/google/devtools/build/lib/cmdline/RepositoryName.java b/src/main/java/com/google/devtools/build/lib/cmdline/RepositoryName.java
index b008978..94705d7 100644
--- a/src/main/java/com/google/devtools/build/lib/cmdline/RepositoryName.java
+++ b/src/main/java/com/google/devtools/build/lib/cmdline/RepositoryName.java
@@ -22,7 +22,6 @@
 import com.google.devtools.build.lib.util.StringCanonicalizer;
 import com.google.devtools.build.lib.util.StringUtilities;
 import com.google.devtools.build.lib.vfs.PathFragment;
-
 import java.io.IOException;
 import java.io.ObjectInputStream;
 import java.io.ObjectOutputStream;
@@ -144,7 +143,7 @@
     }
     try {
       RepositoryName repoName = RepositoryName.create("@" + path.getSegment(1));
-      PathFragment subPath = path.subFragment(2, path.segmentCount());
+      PathFragment subPath = path.subFragment(2);
       return Pair.of(repoName, subPath);
     } catch (LabelSyntaxException e) {
       return null;
diff --git a/src/main/java/com/google/devtools/build/lib/exec/FilesetManifest.java b/src/main/java/com/google/devtools/build/lib/exec/FilesetManifest.java
index 49865e7..319ea6b 100644
--- a/src/main/java/com/google/devtools/build/lib/exec/FilesetManifest.java
+++ b/src/main/java/com/google/devtools/build/lib/exec/FilesetManifest.java
@@ -128,7 +128,7 @@
                     "fileset manifest line must start with '%s': '%s'", workspaceName, location));
           } else {
             // Erase "<workspaceName>/" prefix.
-            location = location.subFragment(1, location.segmentCount());
+            location = location.subFragment(1);
           }
         }
       }
diff --git a/src/main/java/com/google/devtools/build/lib/packages/Package.java b/src/main/java/com/google/devtools/build/lib/packages/Package.java
index ca12997..c37ffa3 100644
--- a/src/main/java/com/google/devtools/build/lib/packages/Package.java
+++ b/src/main/java/com/google/devtools/build/lib/packages/Package.java
@@ -1281,7 +1281,8 @@
       for (OutputFile outputFile : rule.getOutputFiles()) {
         targets.put(outputFile.getName(), outputFile);
         PathFragment outputFileFragment = PathFragment.create(outputFile.getName());
-        for (int i = 1; i < outputFileFragment.segmentCount(); i++) {
+        int segmentCount = outputFileFragment.segmentCount();
+        for (int i = 1; i < segmentCount; i++) {
           String prefix = outputFileFragment.subFragment(0, i).toString();
           outputFilePrefixes.putIfAbsent(prefix, outputFile);
         }
@@ -1473,7 +1474,8 @@
 
         // Check if a prefix of this output file matches an already existing one
         PathFragment outputFileFragment = PathFragment.create(outputFileName);
-        for (int i = 1; i < outputFileFragment.segmentCount(); i++) {
+        int segmentCount = outputFileFragment.segmentCount();
+        for (int i = 1; i < segmentCount; i++) {
           String prefix = outputFileFragment.subFragment(0, i).toString();
           if (outputFiles.containsKey(prefix)) {
             throw conflictingOutputFile(outputFile, outputFiles.get(prefix));
diff --git a/src/main/java/com/google/devtools/build/lib/rules/android/AndroidCommon.java b/src/main/java/com/google/devtools/build/lib/rules/android/AndroidCommon.java
index be9bbf1..6c8e040 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/android/AndroidCommon.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/android/AndroidCommon.java
@@ -324,30 +324,32 @@
     if (needle.equals(PathFragment.EMPTY_FRAGMENT)) {
       return haystack;
     }
+    List<String> needleSegments = needle.getSegments();
     // Compute the overlap offset for duplicated parts of the needle.
-    int[] overlap = new int[needle.segmentCount() + 1];
+    int[] overlap = new int[needleSegments.size() + 1];
     // Start overlap at -1, as it will cancel out the increment in the search.
     // See http://en.wikipedia.org/wiki/Knuth%E2%80%93Morris%E2%80%93Pratt_algorithm for the
     // details.
     overlap[0] = -1;
-    for (int i = 0, j = -1; i < needle.segmentCount(); j++, i++, overlap[i] = j) {
-      while (j >= 0 && !needle.getSegment(i).equals(needle.getSegment(j))) {
+    for (int i = 0, j = -1; i < needleSegments.size(); j++, i++, overlap[i] = j) {
+      while (j >= 0 && !needleSegments.get(i).equals(needleSegments.get(j))) {
         // Walk the overlap until the bound is found.
         j = overlap[j];
       }
     }
     // TODO(corysmith): reverse the search algorithm.
     // Keep the index of the found so that the rightmost index is taken.
+    List<String> haystackSegments = haystack.getSegments();
     int found = -1;
-    for (int i = 0, j = 0; i < haystack.segmentCount(); i++) {
+    for (int i = 0, j = 0; i < haystackSegments.size(); i++) {
 
-      while (j >= 0 && !haystack.getSegment(i).equals(needle.getSegment(j))) {
+      while (j >= 0 && !haystackSegments.get(i).equals(needleSegments.get(j))) {
         // Not matching, walk the needle index to attempt another match.
         j = overlap[j];
       }
       j++;
       // Needle index is exhausted, so the needle must match.
-      if (j == needle.segmentCount()) {
+      if (j == needleSegments.size()) {
         // Record the found index + 1 to be inclusive of the end index.
         found = i + 1;
         // Subtract one from the needle index to restart the search process
diff --git a/src/main/java/com/google/devtools/build/lib/rules/android/LocalResourceContainer.java b/src/main/java/com/google/devtools/build/lib/rules/android/LocalResourceContainer.java
index f11cd18..c754d9e 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/android/LocalResourceContainer.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/android/LocalResourceContainer.java
@@ -32,6 +32,7 @@
 import com.google.devtools.build.lib.vfs.PathFragment;
 import java.util.Arrays;
 import java.util.LinkedHashSet;
+import java.util.List;
 import java.util.Optional;
 import java.util.Set;
 import javax.annotation.Nullable;
@@ -142,7 +143,8 @@
         PathFragment packageRelativePath = file.getRootRelativePath().relativeTo(packageFragment);
         if (packageRelativePath.startsWith(assetsDir)) {
           PathFragment relativePath = packageRelativePath.relativeTo(assetsDir);
-          assetRoots.add(trimTail(file.getExecPath(), relativePath));
+          PathFragment path = file.getExecPath();
+          assetRoots.add(path.subFragment(0, path.segmentCount() - relativePath.segmentCount()));
         } else {
           ruleContext.attributeError(
               ResourceType.ASSETS.getAttribute(),
@@ -273,8 +275,11 @@
         file.getArtifactOwner().getLabel().getPackageIdentifier().getSourceRoot();
     PathFragment packageRelativePath = file.getRootRelativePath().relativeTo(packageFragment);
     try {
+      PathFragment path = file.getExecPath();
       resourceRoots.add(
-          trimTail(file.getExecPath(), makeRelativeTo(resourceDir, packageRelativePath)));
+          path.subFragment(
+              0,
+              path.segmentCount() - segmentCountAfterAncestor(resourceDir, packageRelativePath)));
     } catch (IllegalArgumentException e) {
       ruleErrorConsumer.attributeError(
           resourcesAttr,
@@ -304,7 +309,7 @@
     }
     // TODO(bazel-team): Expand Fileset to verify, or remove Fileset as an option for resources.
     if (artifact.isFileset() || artifact.isTreeArtifact()) {
-      return fragment.subFragment(segmentCount - 1, segmentCount);
+      return fragment.subFragment(segmentCount - 1);
     }
 
     // Check the resource folder type layout.
@@ -320,23 +325,20 @@
     return fragment.subFragment(segmentCount - 3, segmentCount - 2);
   }
 
-  /**
-   * Returns the root-part of a given path by trimming off the end specified by a given tail.
-   * Assumes that the tail is known to match, and simply relies on the segment lengths.
-   */
-  private static PathFragment trimTail(PathFragment path, PathFragment tail) {
-    return path.subFragment(0, path.segmentCount() - tail.segmentCount());
-  }
-
-  private static PathFragment makeRelativeTo(PathFragment ancestor, PathFragment path) {
+  private static int segmentCountAfterAncestor(PathFragment ancestor, PathFragment path) {
     String cutAtSegment = ancestor.getSegment(ancestor.segmentCount() - 1);
-    int totalPathSegments = path.segmentCount() - 1;
-    for (int i = totalPathSegments; i >= 0; i--) {
-      if (path.getSegment(i).equals(cutAtSegment)) {
-        return path.subFragment(i, totalPathSegments);
+    int index = -1;
+    List<String> segments = path.getSegments();
+    for (int i = segments.size() - 1; i >= 0; i--) {
+      if (segments.get(i).equals(cutAtSegment)) {
+        index = i;
+        break;
       }
     }
-    throw new IllegalArgumentException("PathFragment " + path + " is not beneath " + ancestor);
+    if (index == -1) {
+      throw new IllegalArgumentException("PathFragment " + path + " is not beneath " + ancestor);
+    }
+    return segments.size() - index - 1;
   }
 
   private final ImmutableList<Artifact> resources;
diff --git a/src/main/java/com/google/devtools/build/lib/rules/cpp/CcCommon.java b/src/main/java/com/google/devtools/build/lib/rules/cpp/CcCommon.java
index 6737c6c..7b54954 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/cpp/CcCommon.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/cpp/CcCommon.java
@@ -487,7 +487,7 @@
         ruleContext.attributeError("includes",
             "Path references a path above the execution root.");
       }
-      if (includesPath.segmentCount() == 0) {
+      if (includesPath.isEmpty()) {
         ruleContext.attributeError(
             "includes",
             "'"
diff --git a/src/main/java/com/google/devtools/build/lib/rules/cpp/CppCompileAction.java b/src/main/java/com/google/devtools/build/lib/rules/cpp/CppCompileAction.java
index 7bede6c..284be8c 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/cpp/CppCompileAction.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/cpp/CppCompileAction.java
@@ -893,7 +893,7 @@
     }
     // Need to do dir/package matching: first try a quick exact lookup.
     PathFragment includeDir = input.getRootRelativePath().getParentDirectory();
-    if (includeDir.segmentCount() == 0 || declaredIncludeDirs.contains(includeDir)) {
+    if (includeDir.isEmpty() || declaredIncludeDirs.contains(includeDir)) {
       return true;  // OK: quick exact match.
     }
     // Not found in the quick lookup: try the wildcards.
diff --git a/src/main/java/com/google/devtools/build/lib/rules/java/JavaUtil.java b/src/main/java/com/google/devtools/build/lib/rules/java/JavaUtil.java
index eaddad0..ee01342 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/java/JavaUtil.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/java/JavaUtil.java
@@ -157,7 +157,7 @@
   public static PathFragment getJavaPath(PathFragment path) {
     int index = javaSegmentIndex(path);
     if (index >= 0) {
-      return path.subFragment(index + 1, path.segmentCount());
+      return path.subFragment(index + 1);
     }
     return null;
   }
diff --git a/src/main/java/com/google/devtools/build/lib/rules/repository/RepositoryFunction.java b/src/main/java/com/google/devtools/build/lib/rules/repository/RepositoryFunction.java
index 024287d..2b15ced 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/repository/RepositoryFunction.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/repository/RepositoryFunction.java
@@ -509,7 +509,7 @@
       throws IOException, InterruptedException {
     Path externalRepoDir = getExternalRepositoryDirectory(directories);
     PathFragment repositoryPath = rootedPath.asPath().relativeTo(externalRepoDir);
-    if (repositoryPath.segmentCount() == 0) {
+    if (repositoryPath.isEmpty()) {
       // We are the top of the repository path (<outputBase>/external), not in an actual external
       // repository path.
       return;
diff --git a/src/main/java/com/google/devtools/build/lib/skyframe/FilesetEntryFunction.java b/src/main/java/com/google/devtools/build/lib/skyframe/FilesetEntryFunction.java
index 4bf54fc..bedd9ba 100644
--- a/src/main/java/com/google/devtools/build/lib/skyframe/FilesetEntryFunction.java
+++ b/src/main/java/com/google/devtools/build/lib/skyframe/FilesetEntryFunction.java
@@ -149,7 +149,7 @@
         DirectoryTree root = new DirectoryTree();
         for (ResolvedFile f : rftv.getTransitiveFiles().toCollection()) {
           PathFragment path = f.getNameInSymlinkTree().relativeTo(prefixToRemove);
-          if (path.segmentCount() > 0) {
+          if (!path.isEmpty()) {
             path = t.getDestPath().getRelative(path);
             DirectoryTree dir = root;
             for (int i = 0; i < path.segmentCount() - 1; ++i) {
diff --git a/src/main/java/com/google/devtools/build/lib/vfs/PathFragment.java b/src/main/java/com/google/devtools/build/lib/vfs/PathFragment.java
index f385831..9db3aa3 100644
--- a/src/main/java/com/google/devtools/build/lib/vfs/PathFragment.java
+++ b/src/main/java/com/google/devtools/build/lib/vfs/PathFragment.java
@@ -612,6 +612,20 @@
   }
 
   /**
+   * Returns a new path fragment that is a sub fragment of this one. The sub fragment begins at the
+   * specified <code>beginIndex</code> segment and contains the rest of the original path fragment.
+   *
+   * @param beginIndex the beginning index, inclusive.
+   * @return the specified sub fragment, never null.
+   * @exception IndexOutOfBoundsException if the <code>beginIndex</code> is negative, or <code>
+   *     endIndex</code> is larger than the length of this <code>String</code> object, or <code>
+   *     beginIndex</code> is larger than <code>endIndex</code>.
+   */
+  public PathFragment subFragment(int beginIndex) {
+    return subFragment(beginIndex, segments.length);
+  }
+
+  /**
    * Returns true iff the path represented by this object is absolute.
    *
    * <p>True both for UNIX-style absolute paths ("/foo") and Windows-style ("C:/foo"). False for a
@@ -642,6 +656,10 @@
   // windowsVolume).
   public abstract char getDriveLetter();
 
+  public boolean isEmpty() {
+    return segments.length == 0;
+  }
+
   /**
    * Returns the number of segments in this path.
    */
diff --git a/src/main/java/com/google/devtools/build/lib/vfs/WindowsPathFragment.java b/src/main/java/com/google/devtools/build/lib/vfs/WindowsPathFragment.java
index 928c50d..ac3be0f 100644
--- a/src/main/java/com/google/devtools/build/lib/vfs/WindowsPathFragment.java
+++ b/src/main/java/com/google/devtools/build/lib/vfs/WindowsPathFragment.java
@@ -237,10 +237,6 @@
               && HELPER.segmentsEqual(this.segments, otherRelativeWindowsPathFragment.segments);
     }
 
-    private boolean isEmpty() {
-      return segmentCount() == 0;
-    }
-
     // Java serialization looks for the presence of this method in the concrete class. It is not
     // inherited from the parent class.
     @Override
diff --git a/src/main/java/com/google/devtools/build/lib/vfs/inmemoryfs/InMemoryFileSystem.java b/src/main/java/com/google/devtools/build/lib/vfs/inmemoryfs/InMemoryFileSystem.java
index e63d03f..8fd2118 100644
--- a/src/main/java/com/google/devtools/build/lib/vfs/inmemoryfs/InMemoryFileSystem.java
+++ b/src/main/java/com/google/devtools/build/lib/vfs/inmemoryfs/InMemoryFileSystem.java
@@ -377,8 +377,9 @@
         if (traversals > MAX_TRAVERSALS) {
           throw Error.ELOOP.exception(path);
         }
-        for (int ii = linkTarget.segmentCount() - 1; ii >= 0; --ii) {
-          stack.push(linkTarget.getSegment(ii)); // Note this may include ".." segments.
+        List<String> segments = linkTarget.getSegments();
+        for (int ii = segments.size() - 1; ii >= 0; --ii) {
+          stack.push(segments.get(ii)); // Note this may include ".." segments.
         }
       } else {
         inode = child;