[PATCH] D127707: [Clang] Simplify unifying target features

[Joseph Huber via Phabricator via cfe-commits]

jhuber6 created this revision.
jhuber6 added reviewers: yaxunl, jdoerfert, tra.
Herald added a project: All.
jhuber6 requested review of this revision.
Herald added subscribers: cfe-commits, MaskRay.
Herald added a project: clang.

This patch simplifies how we unify target features. Now we simply
iterate the input in reverse and only insert the feature if it hasn't
been seen yet. The only reason we need to reverse this at the end is to
keep the features in order for the existing tests.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D127707

Files:
  clang/lib/Driver/ToolChains/CommonArgs.cpp
  clang/lib/Driver/ToolChains/CommonArgs.h


Index: clang/lib/Driver/ToolChains/CommonArgs.h
===================================================================
--- clang/lib/Driver/ToolChains/CommonArgs.h
+++ clang/lib/Driver/ToolChains/CommonArgs.h
@@ -173,8 +173,7 @@
                                llvm::opt::OptSpecifier Group);
 
 /// If there are multiple +xxx or -xxx features, keep the last one.
-std::vector<StringRef>
-unifyTargetFeatures(const std::vector<StringRef> &Features);
+SmallVector<StringRef> unifyTargetFeatures(ArrayRef<StringRef> Features);
 
 /// Handles the -save-stats option and returns the filename to save statistics
 /// to.
Index: clang/lib/Driver/ToolChains/CommonArgs.cpp
===================================================================
--- clang/lib/Driver/ToolChains/CommonArgs.cpp
+++ clang/lib/Driver/ToolChains/CommonArgs.cpp
@@ -143,28 +143,17 @@
   }
 }
 
-std::vector<StringRef>
-tools::unifyTargetFeatures(const std::vector<StringRef> &Features) {
-  std::vector<StringRef> UnifiedFeatures;
-  // Find the last of each feature.
-  llvm::StringMap<unsigned> LastOpt;
-  for (unsigned I = 0, N = Features.size(); I < N; ++I) {
-    StringRef Name = Features[I];
-    assert(Name[0] == '-' || Name[0] == '+');
-    LastOpt[Name.drop_front(1)] = I;
-  }
-
-  for (unsigned I = 0, N = Features.size(); I < N; ++I) {
-    // If this feature was overridden, ignore it.
-    StringRef Name = Features[I];
-    llvm::StringMap<unsigned>::iterator LastI = LastOpt.find(Name.drop_front(1));
-    assert(LastI != LastOpt.end());
-    unsigned Last = LastI->second;
-    if (Last != I)
-      continue;
-
-    UnifiedFeatures.push_back(Name);
+SmallVector<StringRef>
+tools::unifyTargetFeatures(ArrayRef<StringRef> Features) {
+  // Only add a feature if it hasn't been seen before starting from the end.
+  SmallVector<StringRef> UnifiedFeatures;
+  llvm::DenseSet<StringRef> UsedFeatures;
+  for (StringRef Feature : llvm::reverse(Features)) {
+    if (UsedFeatures.insert(Feature.drop_front()).second)
+      UnifiedFeatures.push_back(Feature);
   }
+
+  std::reverse(UnifiedFeatures.begin(), UnifiedFeatures.end());
   return UnifiedFeatures;
 }
 


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