[Hexagon] Check for offset overflow when reserving scavenging slots

Scavenging slots were only reserved when pseudo-instruction expansion in
frame lowering created new virtual registers. It is possible to still
need a scavenging slot even if no virtual registers were created, in cases
where the stack is large enough to overflow instruction offsets.

llvm-svn: 277355

2 files changed, 16 insertions, 2 deletions

diff --git a/llvm/lib/Target/Hexagon/HexagonFrameLowering.cpp b/llvm/lib/Target/Hexagon/HexagonFrameLowering.cpp
index ed468fe490b..05773440dac 100644
--- a/llvm/lib/Target/Hexagon/HexagonFrameLowering.cpp
+++ b/llvm/lib/Target/Hexagon/HexagonFrameLowering.cpp
@@ -1869,7 +1869,7 @@ void HexagonFrameLowering::determineCalleeSaves(MachineFunction &MF,
 
   // We need to reserve a a spill slot if scavenging could potentially require
   // spilling a scavenged register.
-  if (!NewRegs.empty()) {
+  if (!NewRegs.empty() || mayOverflowFrameOffset(MF)) {
     MachineFrameInfo &MFI = MF.getFrameInfo();
     MachineRegisterInfo &MRI = MF.getRegInfo();
     SetVector<const TargetRegisterClass*> SpillRCs;
@@ -2407,3 +2407,16 @@ bool HexagonFrameLowering::useRestoreFunction(MachineFunction &MF,
                                      : SpillFuncThreshold;
   return Threshold < NumCSI;
 }
+
+
+bool HexagonFrameLowering::mayOverflowFrameOffset(MachineFunction &MF) const {
+  unsigned StackSize = MF.getFrameInfo().estimateStackSize(MF);
+  auto &HST = MF.getSubtarget<HexagonSubtarget>();
+  // A fairly simplistic guess as to whether a potential load/store to a
+  // stack location could require an extra register. It does not account
+  // for store-immediate instructions.
+  if (HST.useHVXOps())
+    return StackSize > 256;
+  return false;
+}
+
diff --git a/llvm/lib/Target/Hexagon/HexagonFrameLowering.h b/llvm/lib/Target/Hexagon/HexagonFrameLowering.h
index b4a39072b72..79e2cf12774 100644
--- a/llvm/lib/Target/Hexagon/HexagonFrameLowering.h
+++ b/llvm/lib/Target/Hexagon/HexagonFrameLowering.h
@@ -141,9 +141,10 @@ private:
 
   void addCalleeSaveRegistersAsImpOperand(MachineInstr *MI, const CSIVect &CSI,
       bool IsDef, bool IsKill) const;
-  bool shouldInlineCSR(llvm::MachineFunction &MF, const CSIVect &CSI) const;
+  bool shouldInlineCSR(MachineFunction &MF, const CSIVect &CSI) const;
   bool useSpillFunction(MachineFunction &MF, const CSIVect &CSI) const;
   bool useRestoreFunction(MachineFunction &MF, const CSIVect &CSI) const;
+  bool mayOverflowFrameOffset(MachineFunction &MF) const;
 };
 
 } // End llvm namespace