[PATCH] D48194: [X86] Initialize FMA3Info directly in its constructor instead of relying on std::call_once

[Craig Topper via Phabricator via llvm-commits]

craig.topper created this revision.
craig.topper added reviewers: spatel, RKSimon, echristo.

FMA3Info only exists as a managed static. As far as I know the ManagedStatic construction proccess is thread safe. It doesn't look like we ever access the ManagedStatic object without immediately doing a query on it that would require the map to be populated. So I don't think we're ever deferring the calculation of the tables from the construction of the object.

So I think we should be able to just populate the FMA3Info map directly in the constructor and get rid of all of the initGroupsOnce stuff.


https://reviews.llvm.org/D48194

Files:
  lib/Target/X86/X86InstrFMA3Info.cpp
  lib/Target/X86/X86InstrFMA3Info.h


Index: lib/Target/X86/X86InstrFMA3Info.h
===================================================================
--- lib/Target/X86/X86InstrFMA3Info.h
+++ lib/Target/X86/X86InstrFMA3Info.h
@@ -171,16 +171,6 @@
   /// from the group.
   DenseMap<unsigned, const X86InstrFMA3Group *> OpcodeToGroup;
 
-  /// Creates groups of FMA opcodes and initializes Opcode-to-Group map.
-  /// This method can be called many times, but the actual initialization is
-  /// called only once.
-  static void initGroupsOnce();
-
-  /// Creates groups of FMA opcodes and initializes Opcode-to-Group map.
-  /// This method must be called ONLY from initGroupsOnce(). Otherwise, such
-  /// call is not thread safe.
-  void initGroupsOnceImpl();
-
   /// Creates one group of FMA opcodes having the register opcodes
   /// \p RegOpcodes and memory opcodes \p MemOpcodes. The parameter \p Attr
   /// specifies the attributes describing the created group.
@@ -203,7 +193,7 @@
   static X86InstrFMA3Info *getX86InstrFMA3Info();
 
   /// Constructor. Just creates an object of the class.
-  X86InstrFMA3Info() = default;
+  X86InstrFMA3Info();
 
   /// Destructor. Deallocates the memory used for FMA3 Groups.
   ~X86InstrFMA3Info() {
@@ -222,9 +212,6 @@
   /// \p Opcode is included. If the given \p Opcode is not recognized as FMA3
   /// and not included into any FMA3 group, then nullptr is returned.
   static const X86InstrFMA3Group *getFMA3Group(unsigned Opcode) {
-    // Ensure that the groups of opcodes are initialized.
-    initGroupsOnce();
-
     // Find the group including the given opcode.
     const X86InstrFMA3Info *FMA3Info = getX86InstrFMA3Info();
     auto I = FMA3Info->OpcodeToGroup.find(Opcode);
@@ -292,7 +279,6 @@
   /// Returns rm_iterator pointing to the first entry of OpcodeToGroup map
   /// with a register FMA opcode having memory form opcode equivalent.
   static rm_iterator rm_begin() {
-    initGroupsOnce();
     const X86InstrFMA3Info *FMA3Info = getX86InstrFMA3Info();
     auto I = FMA3Info->OpcodeToGroup.begin();
     auto E = FMA3Info->OpcodeToGroup.end();
@@ -308,7 +294,6 @@
 
   /// Returns the last rm_iterator.
   static rm_iterator rm_end() {
-    initGroupsOnce();
     return rm_iterator(getX86InstrFMA3Info()->OpcodeToGroup.end());
   }
 };
Index: lib/Target/X86/X86InstrFMA3Info.cpp
===================================================================
--- lib/Target/X86/X86InstrFMA3Info.cpp
+++ lib/Target/X86/X86InstrFMA3Info.cpp
@@ -21,10 +21,6 @@
 
 using namespace llvm;
 
-/// This flag is used in the method llvm::call_once() used below to make the
-/// initialization of the map 'OpcodeToGroup' thread safe.
-static llvm::once_flag InitGroupsOnceFlag;
-
 static ManagedStatic<X86InstrFMA3Info> X86InstrFMA3InfoObj;
 X86InstrFMA3Info *X86InstrFMA3Info::getX86InstrFMA3Info() {
   return &*X86InstrFMA3InfoObj;
@@ -264,7 +260,7 @@
   FMA3_AVX512_VECTOR_GROUP(Name);                                              \
   FMA3_AVX512_SCALAR_GROUP(Name);
 
-void X86InstrFMA3Info::initGroupsOnceImpl() {
+X86InstrFMA3Info::X86InstrFMA3Info() {
   FMA3_AVX2_FULL_GROUP(VFMADD);
   FMA3_AVX2_FULL_GROUP(VFMSUB);
   FMA3_AVX2_FULL_GROUP(VFNMADD);
@@ -281,8 +277,3 @@
   FMA3_AVX512_VECTOR_GROUP(VFMADDSUB);
   FMA3_AVX512_VECTOR_GROUP(VFMSUBADD);
 }
-
-void X86InstrFMA3Info::initGroupsOnce() {
-  llvm::call_once(InitGroupsOnceFlag,
-                  []() { getX86InstrFMA3Info()->initGroupsOnceImpl(); });
-}


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