1 files changed, 30 insertions, 1 deletions
diff --git a/lib/CodeGen/TargetFrameLoweringImpl.cpp b/lib/CodeGen/TargetFrameLoweringImpl.cpp
index b2151eb49655..f0cfa2fbe4fd 100644
--- a/lib/CodeGen/TargetFrameLoweringImpl.cpp
+++ b/lib/CodeGen/TargetFrameLoweringImpl.cpp
@@ -36,6 +36,13 @@ bool TargetFrameLowering::noFramePointerElim(const MachineFunction &MF) const {
   return Attr.getValueAsString() == "true";
 }
 
+bool TargetFrameLowering::enableCalleeSaveSkip(const MachineFunction &MF) const {
+  assert(MF.getFunction().hasFnAttribute(Attribute::NoReturn) &&
+         MF.getFunction().hasFnAttribute(Attribute::NoUnwind) &&
+         !MF.getFunction().hasFnAttribute(Attribute::UWTable));
+  return false;
+}
+
 /// Returns the displacement from the frame register to the stack
 /// frame of the specified index, along with the frame register used
 /// (in output arg FrameReg). This is the default implementation which
@@ -85,6 +92,19 @@ void TargetFrameLowering::determineCalleeSaves(MachineFunction &MF,
   if (MF.getFunction().hasFnAttribute(Attribute::Naked))
     return;
 
+  // Noreturn+nounwind functions never restore CSR, so no saves are needed.
+  // Purely noreturn functions may still return through throws, so those must
+  // save CSR for caller exception handlers.
+  //
+  // If the function uses longjmp to break out of its current path of
+  // execution we do not need the CSR spills either: setjmp stores all CSRs
+  // it was called with into the jmp_buf, which longjmp then restores.
+  if (MF.getFunction().hasFnAttribute(Attribute::NoReturn) &&
+        MF.getFunction().hasFnAttribute(Attribute::NoUnwind) &&
+        !MF.getFunction().hasFnAttribute(Attribute::UWTable) &&
+        enableCalleeSaveSkip(MF))
+    return;
+
   // Functions which call __builtin_unwind_init get all their registers saved.
   bool CallsUnwindInit = MF.callsUnwindInit();
   const MachineRegisterInfo &MRI = MF.getRegInfo();
@@ -100,7 +120,16 @@ unsigned TargetFrameLowering::getStackAlignmentSkew(
   // When HHVM function is called, the stack is skewed as the return address
   // is removed from the stack before we enter the function.
   if (LLVM_UNLIKELY(MF.getFunction().getCallingConv() == CallingConv::HHVM))
-    return MF.getTarget().getPointerSize();
+    return MF.getTarget().getAllocaPointerSize();
 
   return 0;
 }
+
+int TargetFrameLowering::getInitialCFAOffset(const MachineFunction &MF) const {
+  llvm_unreachable("getInitialCFAOffset() not implemented!");
+}
+
+unsigned TargetFrameLowering::getInitialCFARegister(const MachineFunction &MF)
+    const {
+  llvm_unreachable("getInitialCFARegister() not implemented!");
+}
+\ No newline at end of file