Move the segmented stack switch to a function attribute

This removes the -segmented-stacks command line flag in favor of a
per-function "split-stack" attribute.

Patch by Luqman Aden and Alex Crichton!

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@205997 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/CodeGen/CommandFlags.h

@@ -189,11 +189,6 @@ EnablePIE("enable-pie",
           cl::desc("Assume the creation of a position independent executable."),
           cl::init(false));
 
-cl::opt<bool>
-SegmentedStacks("segmented-stacks",
-                cl::desc("Use segmented stacks if possible."),
-                cl::init(false));
-
 cl::opt<bool>
 UseInitArray("use-init-array",
              cl::desc("Use .init_array instead of .ctors."),
@@ -229,7 +224,6 @@ static inline TargetOptions InitTargetOptionsFromCodeGenFlags() {
   Options.StackAlignmentOverride = OverrideStackAlignment;
   Options.TrapFuncName = TrapFuncName;
   Options.PositionIndependentExecutable = EnablePIE;
-  Options.EnableSegmentedStacks = SegmentedStacks;
   Options.UseInitArray = UseInitArray;
   return Options;
 }

include/llvm/CodeGen/MachineFunction.h

@@ -259,6 +259,9 @@ public:
     return MBBNumbering[N];
   }
 
+  /// Should we be emitting segmented stack stuff for the function
+  bool shouldSplitStack();
+
   /// getNumBlockIDs - Return the number of MBB ID's allocated.
   ///
   unsigned getNumBlockIDs() const { return (unsigned)MBBNumbering.size(); }