From 2525e4e4c21c1af3f0f3ed969fb42baa5e37d7e1 Mon Sep 17 00:00:00 2001
From: Matt Arsenault <Matthew.Arsenault@amd.com>
Date: Wed, 17 May 2017 21:23:14 +0000
Subject: [PATCH] AMDGPU: Expand frame indexes to be relative to scratch wave
 offset

In order for an arbitrary callee to access an object
in a caller's stack frame, the 32-bit offset used as
the private pointer needs to be relative to the kernel's
scratch wave offset register.

Convert to this by finding the difference from the current
stack frame and scaling by the wavefront size.

llvm-svn: 303303
---
 llvm/lib/Target/AMDGPU/SIRegisterInfo.cpp | 77 ++++++++++++++++++++++++++++---
 1 file changed, 71 insertions(+), 6 deletions(-)

diff --git a/llvm/lib/Target/AMDGPU/SIRegisterInfo.cpp b/llvm/lib/Target/AMDGPU/SIRegisterInfo.cpp
index 06cfc95..676c508 100644
--- a/llvm/lib/Target/AMDGPU/SIRegisterInfo.cpp
+++ b/llvm/lib/Target/AMDGPU/SIRegisterInfo.cpp
@@ -318,8 +318,11 @@ void SIRegisterInfo::resolveFrameIndex(MachineInstr &MI, unsigned BaseReg,
 
   MachineOperand *FIOp = TII->getNamedOperand(MI, AMDGPU::OpName::vaddr);
   assert(FIOp && FIOp->isFI() && "frame index must be address operand");
-
   assert(TII->isMUBUF(MI));
+  assert(TII->getNamedOperand(MI, AMDGPU::OpName::soffset)->getReg() ==
+         MF->getInfo<SIMachineFunctionInfo>()->getFrameOffsetReg() &&
+         "should only be seeing frame offset relative FrameIndex");
+
 
   MachineOperand *OffsetOp = TII->getNamedOperand(MI, AMDGPU::OpName::offset);
   int64_t NewOffset = OffsetOp->getImm() + Offset;
@@ -981,12 +984,72 @@ void SIRegisterInfo::eliminateFrameIndex(MachineBasicBlock::iterator MI,
     }
 
     default: {
-      if (TII->isMUBUF(*MI)) {
+      const DebugLoc &DL = MI->getDebugLoc();
+      bool IsMUBUF = TII->isMUBUF(*MI);
+
+      if (!IsMUBUF &&
+          MFI->getFrameOffsetReg() != MFI->getScratchWaveOffsetReg()) {
+        // Convert to an absolute stack address by finding the offset from the
+        // scratch wave base and scaling by the wave size.
+        //
+        // In an entry function/kernel the stack address is already the absolute
+        // address relative to the the scratch wave offset.
+
+        unsigned DiffReg
+          = MRI.createVirtualRegister(&AMDGPU::SReg_32_XM0RegClass);
+
+        bool IsCopy = MI->getOpcode() == AMDGPU::V_MOV_B32_e32;
+        unsigned ResultReg = IsCopy ?
+          MI->getOperand(0).getReg() :
+          MRI.createVirtualRegister(&AMDGPU::VGPR_32RegClass);
+
+        BuildMI(*MBB, MI, DL, TII->get(AMDGPU::S_SUB_U32), DiffReg)
+          .addReg(MFI->getFrameOffsetReg())
+          .addReg(MFI->getScratchWaveOffsetReg());
+
+        int64_t Offset = FrameInfo.getObjectOffset(Index);
+        if (Offset == 0) {
+          // XXX - This never happens because of emergency scavenging slot at 0?
+          BuildMI(*MBB, MI, DL, TII->get(AMDGPU::V_LSHRREV_B32_e64), ResultReg)
+            .addImm(Log2_32(ST.getWavefrontSize()))
+            .addReg(DiffReg);
+        } else {
+          unsigned CarryOut
+            = MRI.createVirtualRegister(&AMDGPU::SReg_64_XEXECRegClass);
+          unsigned ScaledReg
+            = MRI.createVirtualRegister(&AMDGPU::SReg_32_XM0RegClass);
+
+          // XXX - Should this use a vector shift?
+          BuildMI(*MBB, MI, DL, TII->get(AMDGPU::S_LSHR_B32), ScaledReg)
+            .addReg(DiffReg, RegState::Kill)
+            .addImm(Log2_32(ST.getWavefrontSize()));
+
+          // TODO: Fold if use instruction is another add of a constant.
+          BuildMI(*MBB, MI, DL, TII->get(AMDGPU::V_ADD_I32_e64), ResultReg)
+            .addReg(CarryOut, RegState::Define | RegState::Dead)
+            .addImm(Offset)
+            .addReg(ScaledReg, RegState::Kill);
+
+          MRI.setRegAllocationHint(CarryOut, 0, AMDGPU::VCC);
+        }
+
+        // Don't introduce an extra copy if we're just materializing in a mov.
+        if (IsCopy)
+          MI->eraseFromParent();
+        else
+          FIOp.ChangeToRegister(ResultReg, false, false, true);
+        return;
+      }
+
+      if (IsMUBUF) {
         // Disable offen so we don't need a 0 vgpr base.
         assert(static_cast<int>(FIOperandNum) ==
                AMDGPU::getNamedOperandIdx(MI->getOpcode(),
                                           AMDGPU::OpName::vaddr));
 
+        assert(TII->getNamedOperand(*MI, AMDGPU::OpName::soffset)->getReg()
+               == MFI->getFrameOffsetReg());
+
         int64_t Offset = FrameInfo.getObjectOffset(Index);
         int64_t OldImm
           = TII->getNamedOperand(*MI, AMDGPU::OpName::offset)->getImm();
@@ -995,17 +1058,19 @@ void SIRegisterInfo::eliminateFrameIndex(MachineBasicBlock::iterator MI,
         if (isUInt<12>(NewOffset) &&
             buildMUBUFOffsetLoadStore(TII, FrameInfo, MI, Index, NewOffset)) {
           MI->eraseFromParent();
-          break;
+          return;
         }
       }
 
+      // If the offset is simply too big, don't convert to a scratch wave offset
+      // relative index.
+
       int64_t Offset = FrameInfo.getObjectOffset(Index);
       FIOp.ChangeToImmediate(Offset);
       if (!TII->isImmOperandLegal(*MI, FIOperandNum, FIOp)) {
         unsigned TmpReg = MRI.createVirtualRegister(&AMDGPU::VGPR_32RegClass);
-        BuildMI(*MBB, MI, MI->getDebugLoc(),
-                TII->get(AMDGPU::V_MOV_B32_e32), TmpReg)
-                .addImm(Offset);
+        BuildMI(*MBB, MI, DL, TII->get(AMDGPU::V_MOV_B32_e32), TmpReg)
+          .addImm(Offset);
         FIOp.ChangeToRegister(TmpReg, false, false, true);
       }
     }
-- 
2.7.4