4 files changed, 39 insertions, 1 deletions
diff --git a/llvm/lib/Target/Hexagon/Hexagon.td b/llvm/lib/Target/Hexagon/Hexagon.td
index 8853dd6d550..dabf37e2887 100644
--- a/llvm/lib/Target/Hexagon/Hexagon.td
+++ b/llvm/lib/Target/Hexagon/Hexagon.td
@@ -60,6 +60,9 @@ def FeatureDuplex: SubtargetFeature<"duplex", "EnableDuplex", "true",
       "Enable generation of duplex instruction">;
 def FeatureReservedR19: SubtargetFeature<"reserved-r19", "ReservedR19",
       "true", "Reserve register R19">;
+def FeatureNoreturnStackElim: SubtargetFeature<"noreturn-stack-elim",
+      "NoreturnStackElim", "true",
+      "Eliminate stack allocation in a noreturn function when possible">;
 
 //===----------------------------------------------------------------------===//
 // Hexagon Instruction Predicate Definitions.
diff --git a/llvm/lib/Target/Hexagon/HexagonFrameLowering.cpp b/llvm/lib/Target/Hexagon/HexagonFrameLowering.cpp
index 2f3e18c99c5..1600ee3a845 100644
--- a/llvm/lib/Target/Hexagon/HexagonFrameLowering.cpp
+++ b/llvm/lib/Target/Hexagon/HexagonFrameLowering.cpp
@@ -550,6 +550,36 @@ void HexagonFrameLowering::emitPrologue(MachineFunction &MF,
   }
 }
 
+/// Returns true if the target can safely skip saving callee-saved registers
+/// for noreturn nounwind functions.
+bool HexagonFrameLowering::enableCalleeSaveSkip(
+    const MachineFunction &MF) const {
+  const auto &F = MF.getFunction();
+  assert(F.hasFnAttribute(Attribute::NoReturn) &&
+         F.getFunction().hasFnAttribute(Attribute::NoUnwind) &&
+         !F.getFunction().hasFnAttribute(Attribute::UWTable));
+
+  // No need to save callee saved registers if the function does not return.
+  return MF.getSubtarget<HexagonSubtarget>().noreturnStackElim();
+}
+
+// Helper function used to determine when to eliminate the stack frame for
+// functions marked as noreturn and when the noreturn-stack-elim options are
+// specified. When both these conditions are true, then a FP may not be needed
+// if the function makes a call. It is very similar to enableCalleeSaveSkip,
+// but it used to check if the allocframe can be eliminated as well.
+static bool enableAllocFrameElim(const MachineFunction &MF) {
+  const auto &F = MF.getFunction();
+  const auto &MFI = MF.getFrameInfo();
+  const auto &HST = MF.getSubtarget<HexagonSubtarget>();
+  assert(!MFI.hasVarSizedObjects() &&
+         !HST.getRegisterInfo()->needsStackRealignment(MF));
+  return F.hasFnAttribute(Attribute::NoReturn) &&
+    F.hasFnAttribute(Attribute::NoUnwind) &&
+    !F.hasFnAttribute(Attribute::UWTable) && HST.noreturnStackElim() &&
+    MFI.getStackSize() == 0;
+}
+
 void HexagonFrameLowering::insertPrologueInBlock(MachineBasicBlock &MBB,
       bool PrologueStubs) const {
   MachineFunction &MF = *MBB.getParent();
@@ -994,7 +1024,7 @@ bool HexagonFrameLowering::hasFP(const MachineFunction &MF) const {
   }
 
   const auto &HMFI = *MF.getInfo<HexagonMachineFunctionInfo>();
-  if (MFI.hasCalls() || HMFI.hasClobberLR())
+  if ((MFI.hasCalls() && !enableAllocFrameElim(MF)) || HMFI.hasClobberLR())
     return true;
 
   return false;
diff --git a/llvm/lib/Target/Hexagon/HexagonFrameLowering.h b/llvm/lib/Target/Hexagon/HexagonFrameLowering.h
index 988718860c5..d65d870750f 100644
--- a/llvm/lib/Target/Hexagon/HexagonFrameLowering.h
+++ b/llvm/lib/Target/Hexagon/HexagonFrameLowering.h
@@ -41,6 +41,8 @@ public:
   void emitEpilogue(MachineFunction &MF, MachineBasicBlock &MBB) const
       override {}
 
+  bool enableCalleeSaveSkip(const MachineFunction &MF) const override;
+
   bool spillCalleeSavedRegisters(MachineBasicBlock &MBB,
       MachineBasicBlock::iterator MI, const std::vector<CalleeSavedInfo> &CSI,
       const TargetRegisterInfo *TRI) const override {
diff --git a/llvm/lib/Target/Hexagon/HexagonSubtarget.h b/llvm/lib/Target/Hexagon/HexagonSubtarget.h
index eaae4db6ba9..de8ac917da5 100644
--- a/llvm/lib/Target/Hexagon/HexagonSubtarget.h
+++ b/llvm/lib/Target/Hexagon/HexagonSubtarget.h
@@ -56,6 +56,7 @@ class HexagonSubtarget : public HexagonGenSubtargetInfo {
   bool HasMemNoShuf = false;
   bool EnableDuplex = false;
   bool ReservedR19 = false;
+  bool NoreturnStackElim = false;
 
 public:
   Hexagon::ArchEnum HexagonArchVersion;
@@ -168,6 +169,8 @@ public:
   bool hasReservedR19() const { return ReservedR19; }
   bool usePredicatedCalls() const;
 
+  bool noreturnStackElim() const { return NoreturnStackElim; }
+
   bool useBSBScheduling() const { return UseBSBScheduling; }
   bool enableMachineScheduler() const override;