R600 -> AMDGPU rename

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@239657 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 605 insertions, 0 deletions

diff --git a/lib/Target/AMDGPU/SILowerControlFlow.cpp b/lib/Target/AMDGPU/SILowerControlFlow.cpp
new file mode 100644
index 00000000000..c319b32111f
--- /dev/null
+++ b/lib/Target/AMDGPU/SILowerControlFlow.cpp
@@ -0,0 +1,605 @@
+//===-- SILowerControlFlow.cpp - Use predicates for control flow ----------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+/// \file
+/// \brief This pass lowers the pseudo control flow instructions to real
+/// machine instructions.
+///
+/// All control flow is handled using predicated instructions and
+/// a predicate stack.  Each Scalar ALU controls the operations of 64 Vector
+/// ALUs.  The Scalar ALU can update the predicate for any of the Vector ALUs
+/// by writting to the 64-bit EXEC register (each bit corresponds to a
+/// single vector ALU).  Typically, for predicates, a vector ALU will write
+/// to its bit of the VCC register (like EXEC VCC is 64-bits, one for each
+/// Vector ALU) and then the ScalarALU will AND the VCC register with the
+/// EXEC to update the predicates.
+///
+/// For example:
+/// %VCC = V_CMP_GT_F32 %VGPR1, %VGPR2
+/// %SGPR0 = SI_IF %VCC
+///   %VGPR0 = V_ADD_F32 %VGPR0, %VGPR0
+/// %SGPR0 = SI_ELSE %SGPR0
+///   %VGPR0 = V_SUB_F32 %VGPR0, %VGPR0
+/// SI_END_CF %SGPR0
+///
+/// becomes:
+///
+/// %SGPR0 = S_AND_SAVEEXEC_B64 %VCC  // Save and update the exec mask
+/// %SGPR0 = S_XOR_B64 %SGPR0, %EXEC  // Clear live bits from saved exec mask
+/// S_CBRANCH_EXECZ label0            // This instruction is an optional
+///                                   // optimization which allows us to
+///                                   // branch if all the bits of
+///                                   // EXEC are zero.
+/// %VGPR0 = V_ADD_F32 %VGPR0, %VGPR0 // Do the IF block of the branch
+///
+/// label0:
+/// %SGPR0 = S_OR_SAVEEXEC_B64 %EXEC   // Restore the exec mask for the Then block
+/// %EXEC = S_XOR_B64 %SGPR0, %EXEC    // Clear live bits from saved exec mask
+/// S_BRANCH_EXECZ label1              // Use our branch optimization
+///                                    // instruction again.
+/// %VGPR0 = V_SUB_F32 %VGPR0, %VGPR   // Do the THEN block
+/// label1:
+/// %EXEC = S_OR_B64 %EXEC, %SGPR0     // Re-enable saved exec mask bits
+//===----------------------------------------------------------------------===//
+
+#include "AMDGPU.h"
+#include "AMDGPUSubtarget.h"
+#include "SIInstrInfo.h"
+#include "SIMachineFunctionInfo.h"
+#include "llvm/CodeGen/MachineFrameInfo.h"
+#include "llvm/CodeGen/MachineFunction.h"
+#include "llvm/CodeGen/MachineFunctionPass.h"
+#include "llvm/CodeGen/MachineInstrBuilder.h"
+#include "llvm/CodeGen/MachineRegisterInfo.h"
+#include "llvm/IR/Constants.h"
+
+using namespace llvm;
+
+namespace {
+
+class SILowerControlFlowPass : public MachineFunctionPass {
+
+private:
+  static const unsigned SkipThreshold = 12;
+
+  static char ID;
+  const SIRegisterInfo *TRI;
+  const SIInstrInfo *TII;
+
+  bool shouldSkip(MachineBasicBlock *From, MachineBasicBlock *To);
+
+  void Skip(MachineInstr &From, MachineOperand &To);
+  void SkipIfDead(MachineInstr &MI);
+
+  void If(MachineInstr &MI);
+  void Else(MachineInstr &MI);
+  void Break(MachineInstr &MI);
+  void IfBreak(MachineInstr &MI);
+  void ElseBreak(MachineInstr &MI);
+  void Loop(MachineInstr &MI);
+  void EndCf(MachineInstr &MI);
+
+  void Kill(MachineInstr &MI);
+  void Branch(MachineInstr &MI);
+
+  void LoadM0(MachineInstr &MI, MachineInstr *MovRel, int Offset = 0);
+  void computeIndirectRegAndOffset(unsigned VecReg, unsigned &Reg, int &Offset);
+  void IndirectSrc(MachineInstr &MI);
+  void IndirectDst(MachineInstr &MI);
+
+public:
+  SILowerControlFlowPass(TargetMachine &tm) :
+    MachineFunctionPass(ID), TRI(nullptr), TII(nullptr) { }
+
+  bool runOnMachineFunction(MachineFunction &MF) override;
+
+  const char *getPassName() const override {
+    return "SI Lower control flow instructions";
+  }
+
+};
+
+} // End anonymous namespace
+
+char SILowerControlFlowPass::ID = 0;
+
+FunctionPass *llvm::createSILowerControlFlowPass(TargetMachine &tm) {
+  return new SILowerControlFlowPass(tm);
+}
+
+bool SILowerControlFlowPass::shouldSkip(MachineBasicBlock *From,
+                                        MachineBasicBlock *To) {
+
+  unsigned NumInstr = 0;
+
+  for (MachineBasicBlock *MBB = From; MBB != To && !MBB->succ_empty();
+       MBB = *MBB->succ_begin()) {
+
+    for (MachineBasicBlock::iterator I = MBB->begin(), E = MBB->end();
+         NumInstr < SkipThreshold && I != E; ++I) {
+
+      if (I->isBundle() || !I->isBundled())
+        if (++NumInstr >= SkipThreshold)
+          return true;
+    }
+  }
+
+  return false;
+}
+
+void SILowerControlFlowPass::Skip(MachineInstr &From, MachineOperand &To) {
+
+  if (!shouldSkip(*From.getParent()->succ_begin(), To.getMBB()))
+    return;
+
+  DebugLoc DL = From.getDebugLoc();
+  BuildMI(*From.getParent(), &From, DL, TII->get(AMDGPU::S_CBRANCH_EXECZ))
+          .addOperand(To)
+          .addReg(AMDGPU::EXEC);
+}
+
+void SILowerControlFlowPass::SkipIfDead(MachineInstr &MI) {
+
+  MachineBasicBlock &MBB = *MI.getParent();
+  DebugLoc DL = MI.getDebugLoc();
+
+  if (MBB.getParent()->getInfo<SIMachineFunctionInfo>()->getShaderType() !=
+      ShaderType::PIXEL ||
+      !shouldSkip(&MBB, &MBB.getParent()->back()))
+    return;
+
+  MachineBasicBlock::iterator Insert = &MI;
+  ++Insert;
+
+  // If the exec mask is non-zero, skip the next two instructions
+  BuildMI(MBB, Insert, DL, TII->get(AMDGPU::S_CBRANCH_EXECNZ))
+          .addImm(3)
+          .addReg(AMDGPU::EXEC);
+
+  // Exec mask is zero: Export to NULL target...
+  BuildMI(MBB, Insert, DL, TII->get(AMDGPU::EXP))
+          .addImm(0)
+          .addImm(0x09) // V_008DFC_SQ_EXP_NULL
+          .addImm(0)
+          .addImm(1)
+          .addImm(1)
+          .addReg(AMDGPU::VGPR0)
+          .addReg(AMDGPU::VGPR0)
+          .addReg(AMDGPU::VGPR0)
+          .addReg(AMDGPU::VGPR0);
+
+  // ... and terminate wavefront
+  BuildMI(MBB, Insert, DL, TII->get(AMDGPU::S_ENDPGM));
+}
+
+void SILowerControlFlowPass::If(MachineInstr &MI) {
+  MachineBasicBlock &MBB = *MI.getParent();
+  DebugLoc DL = MI.getDebugLoc();
+  unsigned Reg = MI.getOperand(0).getReg();
+  unsigned Vcc = MI.getOperand(1).getReg();
+
+  BuildMI(MBB, &MI, DL, TII->get(AMDGPU::S_AND_SAVEEXEC_B64), Reg)
+          .addReg(Vcc);
+
+  BuildMI(MBB, &MI, DL, TII->get(AMDGPU::S_XOR_B64), Reg)
+          .addReg(AMDGPU::EXEC)
+          .addReg(Reg);
+
+  Skip(MI, MI.getOperand(2));
+
+  MI.eraseFromParent();
+}
+
+void SILowerControlFlowPass::Else(MachineInstr &MI) {
+  MachineBasicBlock &MBB = *MI.getParent();
+  DebugLoc DL = MI.getDebugLoc();
+  unsigned Dst = MI.getOperand(0).getReg();
+  unsigned Src = MI.getOperand(1).getReg();
+
+  BuildMI(MBB, MBB.getFirstNonPHI(), DL,
+          TII->get(AMDGPU::S_OR_SAVEEXEC_B64), Dst)
+          .addReg(Src); // Saved EXEC
+
+  BuildMI(MBB, &MI, DL, TII->get(AMDGPU::S_XOR_B64), AMDGPU::EXEC)
+          .addReg(AMDGPU::EXEC)
+          .addReg(Dst);
+
+  Skip(MI, MI.getOperand(2));
+
+  MI.eraseFromParent();
+}
+
+void SILowerControlFlowPass::Break(MachineInstr &MI) {
+  MachineBasicBlock &MBB = *MI.getParent();
+  DebugLoc DL = MI.getDebugLoc();
+
+  unsigned Dst = MI.getOperand(0).getReg();
+  unsigned Src = MI.getOperand(1).getReg();
+ 
+  BuildMI(MBB, &MI, DL, TII->get(AMDGPU::S_OR_B64), Dst)
+          .addReg(AMDGPU::EXEC)
+          .addReg(Src);
+
+  MI.eraseFromParent();
+}
+
+void SILowerControlFlowPass::IfBreak(MachineInstr &MI) {
+  MachineBasicBlock &MBB = *MI.getParent();
+  DebugLoc DL = MI.getDebugLoc();
+
+  unsigned Dst = MI.getOperand(0).getReg();
+  unsigned Vcc = MI.getOperand(1).getReg();
+  unsigned Src = MI.getOperand(2).getReg();
+ 
+  BuildMI(MBB, &MI, DL, TII->get(AMDGPU::S_OR_B64), Dst)
+          .addReg(Vcc)
+          .addReg(Src);
+
+  MI.eraseFromParent();
+}
+
+void SILowerControlFlowPass::ElseBreak(MachineInstr &MI) {
+  MachineBasicBlock &MBB = *MI.getParent();
+  DebugLoc DL = MI.getDebugLoc();
+
+  unsigned Dst = MI.getOperand(0).getReg();
+  unsigned Saved = MI.getOperand(1).getReg();
+  unsigned Src = MI.getOperand(2).getReg();
+ 
+  BuildMI(MBB, &MI, DL, TII->get(AMDGPU::S_OR_B64), Dst)
+          .addReg(Saved)
+          .addReg(Src);
+
+  MI.eraseFromParent();
+}
+
+void SILowerControlFlowPass::Loop(MachineInstr &MI) {
+  MachineBasicBlock &MBB = *MI.getParent();
+  DebugLoc DL = MI.getDebugLoc();
+  unsigned Src = MI.getOperand(0).getReg();
+
+  BuildMI(MBB, &MI, DL, TII->get(AMDGPU::S_ANDN2_B64), AMDGPU::EXEC)
+          .addReg(AMDGPU::EXEC)
+          .addReg(Src);
+
+  BuildMI(MBB, &MI, DL, TII->get(AMDGPU::S_CBRANCH_EXECNZ))
+          .addOperand(MI.getOperand(1))
+          .addReg(AMDGPU::EXEC);
+
+  MI.eraseFromParent();
+}
+
+void SILowerControlFlowPass::EndCf(MachineInstr &MI) {
+  MachineBasicBlock &MBB = *MI.getParent();
+  DebugLoc DL = MI.getDebugLoc();
+  unsigned Reg = MI.getOperand(0).getReg();
+
+  BuildMI(MBB, MBB.getFirstNonPHI(), DL,
+          TII->get(AMDGPU::S_OR_B64), AMDGPU::EXEC)
+          .addReg(AMDGPU::EXEC)
+          .addReg(Reg);
+
+  MI.eraseFromParent();
+}
+
+void SILowerControlFlowPass::Branch(MachineInstr &MI) {
+  if (MI.getOperand(0).getMBB() == MI.getParent()->getNextNode())
+    MI.eraseFromParent();
+
+  // If these aren't equal, this is probably an infinite loop.
+}
+
+void SILowerControlFlowPass::Kill(MachineInstr &MI) {
+  MachineBasicBlock &MBB = *MI.getParent();
+  DebugLoc DL = MI.getDebugLoc();
+  const MachineOperand &Op = MI.getOperand(0);
+
+#ifndef NDEBUG
+  const SIMachineFunctionInfo *MFI
+    = MBB.getParent()->getInfo<SIMachineFunctionInfo>();
+  // Kill is only allowed in pixel / geometry shaders.
+  assert(MFI->getShaderType() == ShaderType::PIXEL ||
+         MFI->getShaderType() == ShaderType::GEOMETRY);
+#endif
+
+  // Clear this thread from the exec mask if the operand is negative
+  if ((Op.isImm())) {
+    // Constant operand: Set exec mask to 0 or do nothing
+    if (Op.getImm() & 0x80000000) {
+      BuildMI(MBB, &MI, DL, TII->get(AMDGPU::S_MOV_B64), AMDGPU::EXEC)
+              .addImm(0);
+    }
+  } else {
+    BuildMI(MBB, &MI, DL, TII->get(AMDGPU::V_CMPX_LE_F32_e32), AMDGPU::VCC)
+           .addImm(0)
+           .addOperand(Op);
+  }
+
+  MI.eraseFromParent();
+}
+
+void SILowerControlFlowPass::LoadM0(MachineInstr &MI, MachineInstr *MovRel, int Offset) {
+
+  MachineBasicBlock &MBB = *MI.getParent();
+  DebugLoc DL = MI.getDebugLoc();
+  MachineBasicBlock::iterator I = MI;
+
+  unsigned Save = MI.getOperand(1).getReg();
+  unsigned Idx = MI.getOperand(3).getReg();
+
+  if (AMDGPU::SReg_32RegClass.contains(Idx)) {
+    if (Offset) {
+      BuildMI(MBB, &MI, DL, TII->get(AMDGPU::S_ADD_I32), AMDGPU::M0)
+              .addReg(Idx)
+              .addImm(Offset);
+    } else {
+      BuildMI(MBB, &MI, DL, TII->get(AMDGPU::S_MOV_B32), AMDGPU::M0)
+              .addReg(Idx);
+    }
+    MBB.insert(I, MovRel);
+  } else {
+
+    assert(AMDGPU::SReg_64RegClass.contains(Save));
+    assert(AMDGPU::VGPR_32RegClass.contains(Idx));
+
+    // Save the EXEC mask
+    BuildMI(MBB, &MI, DL, TII->get(AMDGPU::S_MOV_B64), Save)
+            .addReg(AMDGPU::EXEC);
+
+    // Read the next variant into VCC (lower 32 bits) <- also loop target
+    BuildMI(MBB, &MI, DL, TII->get(AMDGPU::V_READFIRSTLANE_B32),
+            AMDGPU::VCC_LO)
+            .addReg(Idx);
+
+    // Move index from VCC into M0
+    BuildMI(MBB, &MI, DL, TII->get(AMDGPU::S_MOV_B32), AMDGPU::M0)
+            .addReg(AMDGPU::VCC_LO);
+
+    // Compare the just read M0 value to all possible Idx values
+    BuildMI(MBB, &MI, DL, TII->get(AMDGPU::V_CMP_EQ_U32_e32), AMDGPU::VCC)
+            .addReg(AMDGPU::M0)
+            .addReg(Idx);
+
+    // Update EXEC, save the original EXEC value to VCC
+    BuildMI(MBB, &MI, DL, TII->get(AMDGPU::S_AND_SAVEEXEC_B64), AMDGPU::VCC)
+            .addReg(AMDGPU::VCC);
+
+    if (Offset) {
+      BuildMI(MBB, &MI, DL, TII->get(AMDGPU::S_ADD_I32), AMDGPU::M0)
+              .addReg(AMDGPU::M0)
+              .addImm(Offset);
+    }
+    // Do the actual move
+    MBB.insert(I, MovRel);
+
+    // Update EXEC, switch all done bits to 0 and all todo bits to 1
+    BuildMI(MBB, &MI, DL, TII->get(AMDGPU::S_XOR_B64), AMDGPU::EXEC)
+            .addReg(AMDGPU::EXEC)
+            .addReg(AMDGPU::VCC);
+
+    // Loop back to V_READFIRSTLANE_B32 if there are still variants to cover
+    BuildMI(MBB, &MI, DL, TII->get(AMDGPU::S_CBRANCH_EXECNZ))
+            .addImm(-7)
+            .addReg(AMDGPU::EXEC);
+
+    // Restore EXEC
+    BuildMI(MBB, &MI, DL, TII->get(AMDGPU::S_MOV_B64), AMDGPU::EXEC)
+            .addReg(Save);
+
+  }
+  MI.eraseFromParent();
+}
+
+/// \param @VecReg The register which holds element zero of the vector
+///                 being addressed into.
+/// \param[out] @Reg The base register to use in the indirect addressing instruction.
+/// \param[in,out] @Offset As an input, this is the constant offset part of the
+//                         indirect Index. e.g. v0 = v[VecReg + Offset]
+//                         As an output, this is a constant value that needs
+//                         to be added to the value stored in M0.
+void SILowerControlFlowPass::computeIndirectRegAndOffset(unsigned VecReg,
+                                                         unsigned &Reg,
+                                                         int &Offset) {
+  unsigned SubReg = TRI->getSubReg(VecReg, AMDGPU::sub0);
+  if (!SubReg)
+    SubReg = VecReg;
+
+  const TargetRegisterClass *RC = TRI->getPhysRegClass(SubReg);
+  int RegIdx = TRI->getHWRegIndex(SubReg) + Offset;
+
+  if (RegIdx < 0) {
+    Offset = RegIdx;
+    RegIdx = 0;
+  } else {
+    Offset = 0;
+  }
+
+  Reg = RC->getRegister(RegIdx);
+}
+
+void SILowerControlFlowPass::IndirectSrc(MachineInstr &MI) {
+
+  MachineBasicBlock &MBB = *MI.getParent();
+  DebugLoc DL = MI.getDebugLoc();
+
+  unsigned Dst = MI.getOperand(0).getReg();
+  unsigned Vec = MI.getOperand(2).getReg();
+  int Off = MI.getOperand(4).getImm();
+  unsigned Reg;
+
+  computeIndirectRegAndOffset(Vec, Reg, Off);
+
+  MachineInstr *MovRel =
+    BuildMI(*MBB.getParent(), DL, TII->get(AMDGPU::V_MOVRELS_B32_e32), Dst)
+            .addReg(Reg)
+            .addReg(AMDGPU::M0, RegState::Implicit)
+            .addReg(Vec, RegState::Implicit);
+
+  LoadM0(MI, MovRel, Off);
+}
+
+void SILowerControlFlowPass::IndirectDst(MachineInstr &MI) {
+
+  MachineBasicBlock &MBB = *MI.getParent();
+  DebugLoc DL = MI.getDebugLoc();
+
+  unsigned Dst = MI.getOperand(0).getReg();
+  int Off = MI.getOperand(4).getImm();
+  unsigned Val = MI.getOperand(5).getReg();
+  unsigned Reg;
+
+  computeIndirectRegAndOffset(Dst, Reg, Off);
+
+  MachineInstr *MovRel = 
+    BuildMI(*MBB.getParent(), DL, TII->get(AMDGPU::V_MOVRELD_B32_e32))
+            .addReg(Reg, RegState::Define)
+            .addReg(Val)
+            .addReg(AMDGPU::M0, RegState::Implicit)
+            .addReg(Dst, RegState::Implicit);
+
+  LoadM0(MI, MovRel, Off);
+}
+
+bool SILowerControlFlowPass::runOnMachineFunction(MachineFunction &MF) {
+  TII = static_cast<const SIInstrInfo *>(MF.getSubtarget().getInstrInfo());
+  TRI =
+      static_cast<const SIRegisterInfo *>(MF.getSubtarget().getRegisterInfo());
+  SIMachineFunctionInfo *MFI = MF.getInfo<SIMachineFunctionInfo>();
+
+  bool HaveKill = false;
+  bool NeedWQM = false;
+  bool NeedFlat = false;
+  unsigned Depth = 0;
+
+  for (MachineFunction::iterator BI = MF.begin(), BE = MF.end();
+       BI != BE; ++BI) {
+
+    MachineBasicBlock &MBB = *BI;
+    MachineBasicBlock::iterator I, Next;
+    for (I = MBB.begin(); I != MBB.end(); I = Next) {
+      Next = std::next(I);
+
+      MachineInstr &MI = *I;
+      if (TII->isWQM(MI.getOpcode()) || TII->isDS(MI.getOpcode()))
+        NeedWQM = true;
+
+      // Flat uses m0 in case it needs to access LDS.
+      if (TII->isFLAT(MI.getOpcode()))
+        NeedFlat = true;
+
+      switch (MI.getOpcode()) {
+        default: break;
+        case AMDGPU::SI_IF:
+          ++Depth;
+          If(MI);
+          break;
+
+        case AMDGPU::SI_ELSE:
+          Else(MI);
+          break;
+
+        case AMDGPU::SI_BREAK:
+          Break(MI);
+          break;
+
+        case AMDGPU::SI_IF_BREAK:
+          IfBreak(MI);
+          break;
+
+        case AMDGPU::SI_ELSE_BREAK:
+          ElseBreak(MI);
+          break;
+
+        case AMDGPU::SI_LOOP:
+          ++Depth;
+          Loop(MI);
+          break;
+
+        case AMDGPU::SI_END_CF:
+          if (--Depth == 0 && HaveKill) {
+            SkipIfDead(MI);
+            HaveKill = false;
+          }
+          EndCf(MI);
+          break;
+
+        case AMDGPU::SI_KILL:
+          if (Depth == 0)
+            SkipIfDead(MI);
+          else
+            HaveKill = true;
+          Kill(MI);
+          break;
+
+        case AMDGPU::S_BRANCH:
+          Branch(MI);
+          break;
+
+        case AMDGPU::SI_INDIRECT_SRC:
+          IndirectSrc(MI);
+          break;
+
+        case AMDGPU::SI_INDIRECT_DST_V1:
+        case AMDGPU::SI_INDIRECT_DST_V2:
+        case AMDGPU::SI_INDIRECT_DST_V4:
+        case AMDGPU::SI_INDIRECT_DST_V8:
+        case AMDGPU::SI_INDIRECT_DST_V16:
+          IndirectDst(MI);
+          break;
+      }
+    }
+  }
+
+  if (NeedWQM && MFI->getShaderType() == ShaderType::PIXEL) {
+    MachineBasicBlock &MBB = MF.front();
+    BuildMI(MBB, MBB.getFirstNonPHI(), DebugLoc(), TII->get(AMDGPU::S_WQM_B64),
+            AMDGPU::EXEC).addReg(AMDGPU::EXEC);
+  }
+
+  // FIXME: This seems inappropriate to do here.
+  if (NeedFlat && MFI->IsKernel) {
+    // Insert the prologue initializing the SGPRs pointing to the scratch space
+    // for flat accesses.
+    const MachineFrameInfo *FrameInfo = MF.getFrameInfo();
+
+    // TODO: What to use with function calls?
+
+    // FIXME: This is reporting stack size that is used in a scratch buffer
+    // rather than registers as well.
+    uint64_t StackSizeBytes = FrameInfo->getStackSize();
+
+    int IndirectBegin
+      = static_cast<const AMDGPUInstrInfo*>(TII)->getIndirectIndexBegin(MF);
+    // Convert register index to 256-byte unit.
+    uint64_t StackOffset = IndirectBegin < 0 ? 0 : (4 * IndirectBegin / 256);
+
+    assert((StackSizeBytes < 0xffff) && StackOffset < 0xffff &&
+           "Stack limits should be smaller than 16-bits");
+
+    // Initialize the flat scratch register pair.
+    // TODO: Can we use one s_mov_b64 here?
+
+    // Offset is in units of 256-bytes.
+    MachineBasicBlock &MBB = MF.front();
+    DebugLoc NoDL;
+    MachineBasicBlock::iterator Start = MBB.getFirstNonPHI();
+    const MCInstrDesc &SMovK = TII->get(AMDGPU::S_MOVK_I32);
+
+    assert(isInt<16>(StackOffset) && isInt<16>(StackSizeBytes));
+
+    BuildMI(MBB, Start, NoDL, SMovK, AMDGPU::FLAT_SCR_LO)
+      .addImm(StackOffset);
+
+    // Documentation says size is "per-thread scratch size in bytes"
+    BuildMI(MBB, Start, NoDL, SMovK, AMDGPU::FLAT_SCR_HI)
+      .addImm(StackSizeBytes);
+  }
+
+  return true;
+}