IR: Use SmallVector instead of std::vector of TrackingMDRef

Don't use std::vector<TrackingMDRef>, since (at least in some versions
of libc++) std::vector apparently copies values on grow operations
instead of moving them.  Found this when I was temporarily deleting the
copy constructor for TrackingMDRef to investigate a performance
bottleneck.

llvm-svn: 266909

3 files changed, 12 insertions, 3 deletions

diff --git a/llvm/include/llvm/IR/DIBuilder.h b/llvm/include/llvm/IR/DIBuilder.h
index f8f003e8a0c..7ae3860dcd5 100644
--- a/llvm/include/llvm/IR/DIBuilder.h
+++ b/llvm/include/llvm/IR/DIBuilder.h
@@ -51,7 +51,11 @@ namespace llvm {
     bool AllowUnresolvedNodes;
 
     /// Each subprogram's preserved local variables.
-    DenseMap<MDNode *, std::vector<TrackingMDNodeRef>> PreservedVariables;
+    ///
+    /// Do not use a std::vector.  Some versions of libc++ apparently copy
+    /// instead of move on grow operations, and TrackingMDRef is expensive to
+    /// copy.
+    DenseMap<MDNode *, SmallVector<TrackingMDNodeRef, 1>> PreservedVariables;
 
     DIBuilder(const DIBuilder &) = delete;
     void operator=(const DIBuilder &) = delete;
diff --git a/llvm/lib/Bitcode/Reader/BitcodeReader.cpp b/llvm/lib/Bitcode/Reader/BitcodeReader.cpp
index 9c65eecad81..ae1f98f0fd6 100644
--- a/llvm/lib/Bitcode/Reader/BitcodeReader.cpp
+++ b/llvm/lib/Bitcode/Reader/BitcodeReader.cpp
@@ -107,7 +107,12 @@ class BitcodeReaderMetadataList {
   bool AnyFwdRefs;
   unsigned MinFwdRef;
   unsigned MaxFwdRef;
-  std::vector<TrackingMDRef> MetadataPtrs;
+
+  /// Array of metadata references.
+  ///
+  /// Don't use std::vector here.  Some versions of libc++ copy (instead of
+  /// move) on resize, and TrackingMDRef is very expensive to copy.
+  SmallVector<TrackingMDRef, 1> MetadataPtrs;
 
   LLVMContext &Context;
 public:
diff --git a/llvm/lib/IR/DIBuilder.cpp b/llvm/lib/IR/DIBuilder.cpp
index 690918ce8a6..e46de241dfc 100644
--- a/llvm/lib/IR/DIBuilder.cpp
+++ b/llvm/lib/IR/DIBuilder.cpp
@@ -614,7 +614,7 @@ DIGlobalVariable *DIBuilder::createTempGlobalVariableFwdDecl(
 
 static DILocalVariable *createLocalVariable(
     LLVMContext &VMContext,
-    DenseMap<MDNode *, std::vector<TrackingMDNodeRef>> &PreservedVariables,
+    DenseMap<MDNode *, SmallVector<TrackingMDNodeRef, 1>> &PreservedVariables,
     DIScope *Scope, StringRef Name, unsigned ArgNo, DIFile *File,
     unsigned LineNo, DIType *Ty, bool AlwaysPreserve, unsigned Flags) {
   // FIXME: Why getNonCompileUnitScope()?