AMDGPU: Use wider scalar spills for SGPR spilling

Since the spill is for the whole wave, these
don't have the swizzling problems that vector stores do
and a single 4-byte allocation is enough to spill a 64 element
register. This should reduce the number of spill instructions and
put all the spills for a register in the same cacheline.

This should save allocated private size, but for now it doesn't.
The extra slots are allocated for each component, but never used
because the frame layout is essentially finalized before frame
indices are replaced. For always using the scalar store path,
this should probably be moved into processFunctionBeforeFrameFinalized.

llvm-svn: 288445

1 files changed, 70 insertions, 15 deletions

diff --git a/llvm/lib/Target/AMDGPU/SIRegisterInfo.cpp b/llvm/lib/Target/AMDGPU/SIRegisterInfo.cpp
index 936bb8b656f..3c96cc2d7ca 100644
--- a/llvm/lib/Target/AMDGPU/SIRegisterInfo.cpp
+++ b/llvm/lib/Target/AMDGPU/SIRegisterInfo.cpp
@@ -513,6 +513,22 @@ void SIRegisterInfo::buildSpillLoadStore(MachineBasicBlock::iterator MI,
   }
 }
 
+static std::pair<unsigned, unsigned> getSpillEltSize(unsigned SuperRegSize,
+                                                     bool Store) {
+  if (SuperRegSize % 16 == 0) {
+    return { 16, Store ? AMDGPU::S_BUFFER_STORE_DWORDX4_SGPR :
+                         AMDGPU::S_BUFFER_LOAD_DWORDX4_SGPR };
+  }
+
+  if (SuperRegSize % 8 == 0) {
+    return { 8, Store ? AMDGPU::S_BUFFER_STORE_DWORDX2_SGPR :
+                        AMDGPU::S_BUFFER_LOAD_DWORDX2_SGPR };
+  }
+
+  return { 4, Store ? AMDGPU::S_BUFFER_STORE_DWORD_SGPR :
+                      AMDGPU::S_BUFFER_LOAD_DWORD_SGPR};
+}
+
 void SIRegisterInfo::spillSGPR(MachineBasicBlock::iterator MI,
                                int Index,
                                RegScavenger *RS) const {
@@ -522,7 +538,6 @@ void SIRegisterInfo::spillSGPR(MachineBasicBlock::iterator MI,
   const SISubtarget &ST =  MF->getSubtarget<SISubtarget>();
   const SIInstrInfo *TII = ST.getInstrInfo();
 
-  unsigned NumSubRegs = getNumSubRegsForSpillOp(MI->getOpcode());
   unsigned SuperReg = MI->getOperand(0).getReg();
   bool IsKill = MI->getOperand(0).isKill();
   const DebugLoc &DL = MI->getDebugLoc();
@@ -534,7 +549,6 @@ void SIRegisterInfo::spillSGPR(MachineBasicBlock::iterator MI,
 
   assert(SuperReg != AMDGPU::M0 && "m0 should never spill");
 
-  const unsigned EltSize = 4;
   unsigned OffsetReg = AMDGPU::M0;
   unsigned M0CopyReg = AMDGPU::NoRegister;
 
@@ -546,14 +560,40 @@ void SIRegisterInfo::spillSGPR(MachineBasicBlock::iterator MI,
     }
   }
 
+  unsigned ScalarStoreOp;
+  unsigned EltSize = 4;
+  const TargetRegisterClass *RC = getPhysRegClass(SuperReg);
+  if (SpillToSMEM && isSGPRClass(RC)) {
+    // XXX - if private_element_size is larger than 4 it might be useful to be
+    // able to spill wider vmem spills.
+    std::tie(EltSize, ScalarStoreOp) = getSpillEltSize(RC->getSize(), true);
+  }
+
+  const TargetRegisterClass *SubRC = nullptr;
+  unsigned NumSubRegs = 1;
+  ArrayRef<int16_t> SplitParts = getRegSplitParts(RC, EltSize);
+
+  if (!SplitParts.empty()) {
+    NumSubRegs = SplitParts.size();
+    SubRC = getSubRegClass(RC, SplitParts[0]);
+  }
+
   // SubReg carries the "Kill" flag when SubReg == SuperReg.
   unsigned SubKillState = getKillRegState((NumSubRegs == 1) && IsKill);
   for (unsigned i = 0, e = NumSubRegs; i < e; ++i) {
     unsigned SubReg = NumSubRegs == 1 ?
-      SuperReg : getSubReg(SuperReg, getSubRegFromChannel(i));
+      SuperReg : getSubReg(SuperReg, SplitParts[i]);
 
     if (SpillToSMEM) {
       int64_t FrOffset = FrameInfo.getObjectOffset(Index);
+
+      // The allocated memory size is really the wavefront size * the frame
+      // index size. The widest register class is 64 bytes, so a 4-byte scratch
+      // allocation is enough to spill this in a single stack object.
+      //
+      // FIXME: Frame size/offsets are computed earlier than this, so the extra
+      // space is still unnecessarily allocated.
+
       unsigned Align = FrameInfo.getObjectAlignment(Index);
       MachinePointerInfo PtrInfo
         = MachinePointerInfo::getFixedStack(*MF, Index, EltSize * i);
@@ -561,12 +601,10 @@ void SIRegisterInfo::spillSGPR(MachineBasicBlock::iterator MI,
         = MF->getMachineMemOperand(PtrInfo, MachineMemOperand::MOStore,
                                    EltSize, MinAlign(Align, EltSize * i));
 
-      // Add i * 4 wave offset.
-      //
       // SMEM instructions only support a single offset, so increment the wave
       // offset.
 
-      int64_t Offset = ST.getWavefrontSize() * (FrOffset + 4 * i);
+      int64_t Offset = (ST.getWavefrontSize() * FrOffset) + (EltSize * i);
       if (Offset != 0) {
         BuildMI(*MBB, MI, DL, TII->get(AMDGPU::S_ADD_U32), OffsetReg)
           .addReg(MFI->getScratchWaveOffsetReg())
@@ -576,7 +614,7 @@ void SIRegisterInfo::spillSGPR(MachineBasicBlock::iterator MI,
           .addReg(MFI->getScratchWaveOffsetReg());
       }
 
-      BuildMI(*MBB, MI, DL, TII->get(AMDGPU::S_BUFFER_STORE_DWORD_SGPR))
+      BuildMI(*MBB, MI, DL, TII->get(ScalarStoreOp))
         .addReg(SubReg, getKillRegState(IsKill)) // sdata
         .addReg(MFI->getScratchRSrcReg())        // sbase
         .addReg(OffsetReg, RegState::Kill)       // soff
@@ -656,7 +694,6 @@ void SIRegisterInfo::restoreSGPR(MachineBasicBlock::iterator MI,
   const SIInstrInfo *TII = ST.getInstrInfo();
   const DebugLoc &DL = MI->getDebugLoc();
 
-  unsigned NumSubRegs = getNumSubRegsForSpillOp(MI->getOpcode());
   unsigned SuperReg = MI->getOperand(0).getReg();
   bool SpillToSMEM = ST.hasScalarStores() && EnableSpillSGPRToSMEM;
 
@@ -673,16 +710,34 @@ void SIRegisterInfo::restoreSGPR(MachineBasicBlock::iterator MI,
     }
   }
 
+  unsigned EltSize = 4;
+  unsigned ScalarLoadOp;
+
+  const TargetRegisterClass *RC = getPhysRegClass(SuperReg);
+  if (SpillToSMEM && isSGPRClass(RC)) {
+    // XXX - if private_element_size is larger than 4 it might be useful to be
+    // able to spill wider vmem spills.
+    std::tie(EltSize, ScalarLoadOp) = getSpillEltSize(RC->getSize(), false);
+  }
+
+  const TargetRegisterClass *SubRC = nullptr;
+  unsigned NumSubRegs = 1;
+  ArrayRef<int16_t> SplitParts = getRegSplitParts(RC, EltSize);
+
+  if (!SplitParts.empty()) {
+    NumSubRegs = SplitParts.size();
+    SubRC = getSubRegClass(RC, SplitParts[0]);
+  }
+
   // SubReg carries the "Kill" flag when SubReg == SuperReg.
   int64_t FrOffset = FrameInfo.getObjectOffset(Index);
 
-  const unsigned EltSize = 4;
-
   for (unsigned i = 0, e = NumSubRegs; i < e; ++i) {
     unsigned SubReg = NumSubRegs == 1 ?
-      SuperReg : getSubReg(SuperReg, getSubRegFromChannel(i));
+      SuperReg : getSubReg(SuperReg, SplitParts[i]);
 
     if (SpillToSMEM) {
+      // FIXME: Size may be > 4 but extra bytes wasted.
       unsigned Align = FrameInfo.getObjectAlignment(Index);
       MachinePointerInfo PtrInfo
         = MachinePointerInfo::getFixedStack(*MF, Index, EltSize * i);
@@ -691,7 +746,7 @@ void SIRegisterInfo::restoreSGPR(MachineBasicBlock::iterator MI,
                                    EltSize, MinAlign(Align, EltSize * i));
 
       // Add i * 4 offset
-      int64_t Offset = ST.getWavefrontSize() * (FrOffset + 4 * i);
+      int64_t Offset = (ST.getWavefrontSize() * FrOffset) + (EltSize * i);
       if (Offset != 0) {
         BuildMI(*MBB, MI, DL, TII->get(AMDGPU::S_ADD_U32), OffsetReg)
           .addReg(MFI->getScratchWaveOffsetReg())
@@ -702,14 +757,14 @@ void SIRegisterInfo::restoreSGPR(MachineBasicBlock::iterator MI,
       }
 
       auto MIB =
-        BuildMI(*MBB, MI, DL, TII->get(AMDGPU::S_BUFFER_LOAD_DWORD_SGPR), SubReg)
+        BuildMI(*MBB, MI, DL, TII->get(ScalarLoadOp), SubReg)
         .addReg(MFI->getScratchRSrcReg()) // sbase
         .addReg(OffsetReg, RegState::Kill)                // soff
         .addImm(0)                        // glc
         .addMemOperand(MMO);
 
       if (NumSubRegs > 1)
-        MIB.addReg(MI->getOperand(0).getReg(), RegState::ImplicitDefine);
+        MIB.addReg(SuperReg, RegState::ImplicitDefine);
 
       continue;
     }
@@ -725,7 +780,7 @@ void SIRegisterInfo::restoreSGPR(MachineBasicBlock::iterator MI,
         .addImm(Spill.Lane);
 
       if (NumSubRegs > 1)
-        MIB.addReg(MI->getOperand(0).getReg(), RegState::ImplicitDefine);
+        MIB.addReg(SuperReg, RegState::ImplicitDefine);
     } else {
       // Restore SGPR from a stack slot.
       // FIXME: We should use S_LOAD_DWORD here for VI.