A small refactoring + adding comments.

SelectionDAGIsel::LowerArguments needs a function, not a basic block. So it
makes sense to pass it the function instead of extracting a basic-block from
the function and then tossing it. This is also more self-documenting (functions
have arguments, BBs don't).

In addition, added comments to a couple of Select* methods.

llvm-svn: 176305

llvm/include/llvm/CodeGen/SelectionDAGISel.h

@@ -249,16 +249,26 @@ private:
                     const SDValue *Ops, unsigned NumOps, unsigned EmitNodeInfo);
 
   void PrepareEHLandingPad();
+
+  /// \brief Perform instruction selection on all basic blocks in the function.
   void SelectAllBasicBlocks(const Function &Fn);
+
+  /// \brief Perform instruction selection on a single basic block, for
+  /// instructions between \p Begin and \p End.  \p HadTailCall will be set
+  /// to true if a call in the block was translated as a tail call.
+  void SelectBasicBlock(BasicBlock::const_iterator Begin,
+                        BasicBlock::const_iterator End,
+                        bool &HadTailCall);
+
   bool TryToFoldFastISelLoad(const LoadInst *LI, const Instruction *FoldInst,
                              FastISel *FastIS);
   void FinishBasicBlock();
 
-  void SelectBasicBlock(BasicBlock::const_iterator Begin,
-                        BasicBlock::const_iterator End,
-                        bool &HadTailCall);
   void CodeGenAndEmitDAG();
-  void LowerArguments(const BasicBlock *BB);
+
+  /// \brief Generate instructions for lowering the incoming arguments of the
+  /// given function.
+  void LowerArguments(const Function &F);
 
   void ComputeLiveOutVRegInfo();
 

llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp

@@ -6596,9 +6596,7 @@ static bool isOnlyUsedInEntryBlock(const Argument *A, bool FastISel) {
   return true;
 }
 
-void SelectionDAGISel::LowerArguments(const BasicBlock *LLVMBB) {
-  // If this is the entry block, emit arguments.
-  const Function &F = *LLVMBB->getParent();
+void SelectionDAGISel::LowerArguments(const Function &F) {
   SelectionDAG &DAG = SDB->DAG;
   DebugLoc dl = SDB->getCurDebugLoc();
   const DataLayout *TD = TLI.getDataLayout();

llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp

@@ -1054,15 +1054,12 @@ void SelectionDAGISel::SelectAllBasicBlocks(const Function &Fn) {
       if (LLVMBB == &Fn.getEntryBlock()) {
         // Lower any arguments needed in this block if this is the entry block.
         if (!FastIS->LowerArguments()) {
-
+          // Fast isel failed to lower these arguments
           if (EnableFastISelAbortArgs)
-            // The "fast" selector couldn't lower these arguments.  For the
-            // purpose of debugging, just abort.
             llvm_unreachable("FastISel didn't lower all arguments");
 
-          // Call target indepedent SDISel argument lowering code if the target
-          // specific routine is not successful.
-          LowerArguments(LLVMBB);
+          // Use SelectionDAG argument lowering
+          LowerArguments(Fn);
           CurDAG->setRoot(SDB->getControlRoot());
           SDB->clear();
           CodeGenAndEmitDAG();
@@ -1181,7 +1178,7 @@ void SelectionDAGISel::SelectAllBasicBlocks(const Function &Fn) {
     } else {
       // Lower any arguments needed in this block if this is the entry block.
       if (LLVMBB == &Fn.getEntryBlock())
-        LowerArguments(LLVMBB);
+        LowerArguments(Fn);
     }
 
     if (Begin != BI)