AMDGPU: Don't use stack space for SGPR->VGPR spills

Before frame offsets are calculated, try to eliminate the
frame indexes used by SGPR spills. Then we can delete them
after.

I think for now we can be sure that no other instruction
will be re-using the same frame indexes. It should be easy
to notice if this assumption ever breaks since everything
asserts if it tries to use a dead frame index later.

The unused emergency stack slot seems to still be left behind,
so an additional 4 bytes is still wasted.

llvm-svn: 295753

1 files changed, 22 insertions, 7 deletions

diff --git a/llvm/lib/Target/AMDGPU/SIRegisterInfo.h b/llvm/lib/Target/AMDGPU/SIRegisterInfo.h
index c95492ffd22..679ed229758 100644
--- a/llvm/lib/Target/AMDGPU/SIRegisterInfo.h
+++ b/llvm/lib/Target/AMDGPU/SIRegisterInfo.h
@@ -21,8 +21,8 @@
 
 namespace llvm {
 
-class SISubtarget;
 class MachineRegisterInfo;
+class SISubtarget;
 class SIMachineFunctionInfo;
 
 class SIRegisterInfo final : public AMDGPURegisterInfo {
@@ -31,13 +31,22 @@ private:
   unsigned VGPRSetID;
   BitVector SGPRPressureSets;
   BitVector VGPRPressureSets;
+  bool SpillSGPRToVGPR;
+  bool SpillSGPRToSMEM;
 
   void reserveRegisterTuples(BitVector &, unsigned Reg) const;
   void classifyPressureSet(unsigned PSetID, unsigned Reg,
                            BitVector &PressureSets) const;
-
 public:
-  SIRegisterInfo();
+  SIRegisterInfo(const SISubtarget &ST);
+
+  bool spillSGPRToVGPR() const {
+    return SpillSGPRToVGPR;
+  }
+
+  bool spillSGPRToSMEM() const {
+    return SpillSGPRToSMEM;
+  }
 
   /// Return the end register initially reserved for the scratch buffer in case
   /// spilling is needed.
@@ -78,16 +87,22 @@ public:
   const TargetRegisterClass *getPointerRegClass(
     const MachineFunction &MF, unsigned Kind = 0) const override;
 
-  void spillSGPR(MachineBasicBlock::iterator MI,
-                 int FI, RegScavenger *RS) const;
+  /// If \p OnlyToVGPR is true, this will only succeed if this
+  bool spillSGPR(MachineBasicBlock::iterator MI,
+                 int FI, RegScavenger *RS,
+                 bool OnlyToVGPR = false) const;
 
-  void restoreSGPR(MachineBasicBlock::iterator MI,
-                   int FI, RegScavenger *RS) const;
+  bool restoreSGPR(MachineBasicBlock::iterator MI,
+                   int FI, RegScavenger *RS,
+                   bool OnlyToVGPR = false) const;
 
   void eliminateFrameIndex(MachineBasicBlock::iterator MI, int SPAdj,
                            unsigned FIOperandNum,
                            RegScavenger *RS) const override;
 
+  bool eliminateSGPRToVGPRSpillFrameIndex(MachineBasicBlock::iterator MI,
+                                          int FI, RegScavenger *RS) const;
+
   unsigned getHWRegIndex(unsigned Reg) const {
     return getEncodingValue(Reg) & 0xff;
   }