Revert "[Hexagon] Handle decreasing of stack alignment in frame lowering"

This breaks passing of aligned function arguments.

llvm-svn: 306145

4 files changed, 2 insertions, 51 deletions

diff --git a/llvm/lib/Target/Hexagon/HexagonFrameLowering.cpp b/llvm/lib/Target/Hexagon/HexagonFrameLowering.cpp
index 601a5d303cd..f0b7f587379 100644
--- a/llvm/lib/Target/Hexagon/HexagonFrameLowering.cpp
+++ b/llvm/lib/Target/Hexagon/HexagonFrameLowering.cpp
@@ -552,7 +552,7 @@ void HexagonFrameLowering::insertPrologueInBlock(MachineBasicBlock &MBB,
   auto &HRI = *HST.getRegisterInfo();
   DebugLoc dl;
 
-  unsigned MaxAlign = std::max(getMaxStackAlignment(MF), getStackAlignment());
+  unsigned MaxAlign = std::max(MFI.getMaxAlignment(), getStackAlignment());
 
   // Calculate the total stack frame size.
   // Get the number of bytes to allocate from the FrameInfo.
@@ -2354,26 +2354,11 @@ void HexagonFrameLowering::expandAlloca(MachineInstr *AI,
   }
 }
 
-unsigned
-HexagonFrameLowering::getMaxStackAlignment(const MachineFunction &MF) const {
-  const MachineFrameInfo &MFI = MF.getFrameInfo();
-  // MFI's MaxAlignment can only grow, but we can actually reduce it
-  // for vector spills.
-  unsigned MaxAlign = 0;
-  for (int i = 0, e = MFI.getObjectIndexEnd(); i != e; ++i) {
-    if (MFI.isDeadObjectIndex(i))
-      continue;
-    unsigned Align = MFI.getObjectAlignment(i);
-    MaxAlign = std::max(MaxAlign, Align);
-  }
-  return MaxAlign;
-}
-
 bool HexagonFrameLowering::needsAligna(const MachineFunction &MF) const {
   const MachineFrameInfo &MFI = MF.getFrameInfo();
   if (!MFI.hasVarSizedObjects())
     return false;
-  unsigned MaxA = getMaxStackAlignment(MF);
+  unsigned MaxA = MFI.getMaxAlignment();
   if (MaxA <= getStackAlignment())
     return false;
   return true;
diff --git a/llvm/lib/Target/Hexagon/HexagonFrameLowering.h b/llvm/lib/Target/Hexagon/HexagonFrameLowering.h
index 29bafaee78c..529a61d4a5b 100644
--- a/llvm/lib/Target/Hexagon/HexagonFrameLowering.h
+++ b/llvm/lib/Target/Hexagon/HexagonFrameLowering.h
@@ -82,8 +82,6 @@ public:
       const TargetRegisterInfo *TRI, std::vector<CalleeSavedInfo> &CSI)
       const override;
 
-  unsigned getMaxStackAlignment(const MachineFunction &MF) const;
-
   bool needsAligna(const MachineFunction &MF) const;
   const MachineInstr *getAlignaInstr(const MachineFunction &MF) const;
 
diff --git a/llvm/lib/Target/Hexagon/HexagonRegisterInfo.cpp b/llvm/lib/Target/Hexagon/HexagonRegisterInfo.cpp
index b44177b0a35..1fc157900ed 100644
--- a/llvm/lib/Target/Hexagon/HexagonRegisterInfo.cpp
+++ b/llvm/lib/Target/Hexagon/HexagonRegisterInfo.cpp
@@ -283,36 +283,6 @@ bool HexagonRegisterInfo::useFPForScavengingIndex(const MachineFunction &MF)
   return MF.getSubtarget<HexagonSubtarget>().getFrameLowering()->hasFP(MF);
 }
 
-// The stack alignment on Hexagon can actually decrease in some cases,
-// specifically in some subset of cases when a variable-sized stack object
-// is present.
-// The issue is two-fold:
-// First of all, if there is a variable-sized object and the stack needs
-// extra alignment (due to pre-existing local objects), then a special
-// register will be reserved up front, acting as the aligned stack pointer
-// (call it AP). This register is only guaranteed to be live for accessing
-// these pre-existing local objects (the ones with the higher alignment).
-// Now, if the register allocator introduces vector register spills, their
-// spill slots will initially have an alignment equal to the register size,
-// which is higher than the normal stack alignment. Ideally, they should be
-// loaded/stored using AP, but AP may not be available at all required
-// places. To avoid this issue, the vector spill slots will have their
-// alignment lowered to 8, and they will be loaded/stored using unaligned
-// instructions.
-//
-// The lowering of the stack alignment may happen if the stack had a
-// variable-sized object, but otherwise retained its default alignment
-// up until register allocation. If the register allocator introduces
-// a vector spill, it will cause the max stack alignment to grow
-// (inside MachineFrameInfo). When the alignment of the spills is reset
-// back to the default stack alignment, MFI's max stack alignment will
-// not reflect that (since it cannot be lowered). Relying on that during
-// frame lowering will cause an unnecessary stack realignment.
-bool HexagonRegisterInfo::needsStackRealignment(const MachineFunction &MF)
-      const {
-  auto &HFI = *MF.getSubtarget<HexagonSubtarget>().getFrameLowering();
-  return HFI.getMaxStackAlignment(MF) > HFI.getStackAlignment();
-}
 
 unsigned HexagonRegisterInfo::getFirstCallerSavedNonParamReg() const {
   return Hexagon::R6;
diff --git a/llvm/lib/Target/Hexagon/HexagonRegisterInfo.h b/llvm/lib/Target/Hexagon/HexagonRegisterInfo.h
index 568bdd0b806..5f65fad2cc0 100644
--- a/llvm/lib/Target/Hexagon/HexagonRegisterInfo.h
+++ b/llvm/lib/Target/Hexagon/HexagonRegisterInfo.h
@@ -55,8 +55,6 @@ public:
     return true;
   }
 
-  bool needsStackRealignment(const MachineFunction &MF) const;
-
   /// Returns true if the frame pointer is valid.
   bool useFPForScavengingIndex(const MachineFunction &MF) const override;