[WebAssembly] Implement red zone for user stack

Implements a mostly-conventional redzone for the userspace
stack. Because we have unsigned load/store offsets we continue to use a
local SP subtracted from the incoming SP but do not write it back to
memory.

Differential Revision: http://reviews.llvm.org/D17525

llvm-svn: 261662

1 files changed, 8 insertions, 0 deletions

diff --git a/llvm/lib/Target/WebAssembly/WebAssemblyFrameLowering.h b/llvm/lib/Target/WebAssembly/WebAssemblyFrameLowering.h
index 39f3f04e68d..cb3b011aeb8 100644
--- a/llvm/lib/Target/WebAssembly/WebAssemblyFrameLowering.h
+++ b/llvm/lib/Target/WebAssembly/WebAssemblyFrameLowering.h
@@ -19,9 +19,12 @@
 #include "llvm/Target/TargetFrameLowering.h"
 
 namespace llvm {
+class MachineFrameInfo;
 
 class WebAssemblyFrameLowering final : public TargetFrameLowering {
  public:
+  static const size_t RedZoneSize = 128;
+
   WebAssemblyFrameLowering()
       : TargetFrameLowering(StackGrowsDown, /*StackAlignment=*/16,
                             /*LocalAreaOffset=*/0,
@@ -38,6 +41,11 @@ class WebAssemblyFrameLowering final : public TargetFrameLowering {
 
   bool hasFP(const MachineFunction &MF) const override;
   bool hasReservedCallFrame(const MachineFunction &MF) const override;
+
+ private:
+  bool needsSP(const MachineFunction &MF, const MachineFrameInfo &MFI) const;
+  bool needsSPWriteback(const MachineFunction &MF,
+                        const MachineFrameInfo &MFI) const;
 };
 
 }  // end namespace llvm