CodeGen: Canonicalize access to function attributes, NFC

Canonicalize access to function attributes to use the simpler API.

getAttributes().getAttribute(AttributeSet::FunctionIndex, Kind)
  => getFnAttribute(Kind)

getAttributes().hasAttribute(AttributeSet::FunctionIndex, Kind)
  => hasFnAttribute(Kind)

Also, add `Function::getFnStackAlignment()`, and canonicalize:

getAttributes().getStackAlignment(AttributeSet::FunctionIndex)
  => getFnStackAlignment()

llvm-svn: 229208
diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
index 408a25b..b9f53bd 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -3971,9 +3971,7 @@
   bool DstAlignCanChange = false;
   MachineFunction &MF = DAG.getMachineFunction();
   MachineFrameInfo *MFI = MF.getFrameInfo();
-  bool OptSize =
-    MF.getFunction()->getAttributes().
-      hasAttribute(AttributeSet::FunctionIndex, Attribute::OptimizeForSize);
+  bool OptSize = MF.getFunction()->hasFnAttribute(Attribute::OptimizeForSize);
   FrameIndexSDNode *FI = dyn_cast<FrameIndexSDNode>(Dst);
   if (FI && !MFI->isFixedObjectIndex(FI->getIndex()))
     DstAlignCanChange = true;
@@ -4086,8 +4084,7 @@
   bool DstAlignCanChange = false;
   MachineFunction &MF = DAG.getMachineFunction();
   MachineFrameInfo *MFI = MF.getFrameInfo();
-  bool OptSize = MF.getFunction()->getAttributes().
-    hasAttribute(AttributeSet::FunctionIndex, Attribute::OptimizeForSize);
+  bool OptSize = MF.getFunction()->hasFnAttribute(Attribute::OptimizeForSize);
   FrameIndexSDNode *FI = dyn_cast<FrameIndexSDNode>(Dst);
   if (FI && !MFI->isFixedObjectIndex(FI->getIndex()))
     DstAlignCanChange = true;
@@ -4181,8 +4178,7 @@
   bool DstAlignCanChange = false;
   MachineFunction &MF = DAG.getMachineFunction();
   MachineFrameInfo *MFI = MF.getFrameInfo();
-  bool OptSize = MF.getFunction()->getAttributes().
-    hasAttribute(AttributeSet::FunctionIndex, Attribute::OptimizeForSize);
+  bool OptSize = MF.getFunction()->hasFnAttribute(Attribute::OptimizeForSize);
   FrameIndexSDNode *FI = dyn_cast<FrameIndexSDNode>(Dst);
   if (FI && !MFI->isFixedObjectIndex(FI->getIndex()))
     DstAlignCanChange = true;