[clang] c4a2674 - [Clang] Simplify unifying target features

[Joseph Huber via cfe-commits]

Author: Joseph Huber
Date: 2022-06-14T15:58:16-04:00
New Revision: c4a2674e21c4f5ffd46f90982ce3c3d952018e66

URL: https://github.com/llvm/llvm-project/commit/c4a2674e21c4f5ffd46f90982ce3c3d952018e66
DIFF: https://github.com/llvm/llvm-project/commit/c4a2674e21c4f5ffd46f90982ce3c3d952018e66.diff

LOG: [Clang] Simplify unifying target features

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.

Reviewed By: tra

Differential Revision: https://reviews.llvm.org/D127707

Added: 
    

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

Removed: 
    


################################################################################
diff  --git a/clang/lib/Driver/ToolChains/CommonArgs.cpp b/clang/lib/Driver/ToolChains/CommonArgs.cpp
index 7be25072c62e6..accf79f767249 100644
--- a/clang/lib/Driver/ToolChains/CommonArgs.cpp
+++ b/clang/lib/Driver/ToolChains/CommonArgs.cpp
@@ -143,28 +143,16 @@ void tools::handleTargetFeaturesGroup(const ArgList &Args,
   }
 }
 
-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.insert(UnifiedFeatures.begin(), Feature);
   }
+
   return UnifiedFeatures;
 }
 

diff  --git a/clang/lib/Driver/ToolChains/CommonArgs.h b/clang/lib/Driver/ToolChains/CommonArgs.h
index b0238612234c5..3052cbf1a3c38 100644
--- a/clang/lib/Driver/ToolChains/CommonArgs.h
+++ b/clang/lib/Driver/ToolChains/CommonArgs.h
@@ -173,8 +173,7 @@ void handleTargetFeaturesGroup(const llvm::opt::ArgList &Args,
                                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.