AMDGPU: Use copy instead of mov during frame lowering

[arsenm]

Summary

This occurs before RA pseudos are expanded. It's less code to emit the copy.

[• tstellarAMD]

LGTM.

[arsenm]

r280297

lib/Target/AMDGPU/SIFrameLowering.cpp

unsigned FlatScratchInitReg
     = TRI->getPreloadedValue(MF, SIRegisterInfo::FLAT_SCRATCH_INIT);
 
   MachineRegisterInfo &MRI = MF.getRegInfo();
   MRI.addLiveIn(FlatScratchInitReg);
   MBB.addLiveIn(FlatScratchInitReg);
 
   // Copy the size in bytes.
   unsigned FlatScrInitHi = TRI->getSubReg(FlatScratchInitReg, AMDGPU::sub1);
-  BuildMI(MBB, I, DL, TII->get(AMDGPU::S_MOV_B32), AMDGPU::FLAT_SCR_LO)
+  BuildMI(MBB, I, DL, TII->get(AMDGPU::COPY), AMDGPU::FLAT_SCR_LO)
     .addReg(FlatScrInitHi, RegState::Kill);
 
   unsigned FlatScrInitLo = TRI->getSubReg(FlatScratchInitReg, AMDGPU::sub0);
 
   const SIMachineFunctionInfo *MFI = MF.getInfo<SIMachineFunctionInfo>();
   unsigned ScratchWaveOffsetReg = MFI->getScratchWaveOffsetReg();
 
 
void SIFrameLowering::emitPrologue(MachineFunction &MF,
   for (MachineBasicBlock &OtherBB : MF) {
     if (&OtherBB == &MBB)
       continue;
 
     OtherBB.addLiveIn(ScratchRsrcReg);
     OtherBB.addLiveIn(ScratchWaveOffsetReg);
   }
 
-  const MCInstrDesc &SMovB32 = TII->get(AMDGPU::S_MOV_B32);
   DebugLoc DL;
   MachineBasicBlock::iterator I = MBB.begin();
 
   if (PreloadedScratchWaveOffsetReg != ScratchWaveOffsetReg) {
     // Make sure we emit the copy for the offset first. We may have chosen to
     // copy the buffer resource into a register that aliases the input offset
     // register.
-    BuildMI(MBB, I, DL, SMovB32, ScratchWaveOffsetReg)
+    BuildMI(MBB, I, DL, TII->get(AMDGPU::COPY), ScratchWaveOffsetReg)
       .addReg(PreloadedScratchWaveOffsetReg, RegState::Kill);
   }
 
   if (ST.isAmdHsaOS()) {
     // Insert copies from argument register.
     assert(
       !TRI->isSubRegisterEq(PreloadedPrivateBufferReg, ScratchRsrcReg) &&
       !TRI->isSubRegisterEq(PreloadedPrivateBufferReg, ScratchWaveOffsetReg));
 
-    unsigned Rsrc01 = TRI->getSubReg(ScratchRsrcReg, AMDGPU::sub0_sub1);
-    unsigned Rsrc23 = TRI->getSubReg(ScratchRsrcReg, AMDGPU::sub2_sub3);
-
-    unsigned Lo = TRI->getSubReg(PreloadedPrivateBufferReg, AMDGPU::sub0_sub1);
-    unsigned Hi = TRI->getSubReg(PreloadedPrivateBufferReg, AMDGPU::sub2_sub3);
-
-    const MCInstrDesc &SMovB64 = TII->get(AMDGPU::S_MOV_B64);
-
-    BuildMI(MBB, I, DL, SMovB64, Rsrc01)
-      .addReg(Lo, RegState::Kill);
-    BuildMI(MBB, I, DL, SMovB64, Rsrc23)
-      .addReg(Hi, RegState::Kill);
+    BuildMI(MBB, I, DL, TII->get(AMDGPU::COPY), ScratchRsrcReg)
+      .addReg(PreloadedPrivateBufferReg, RegState::Kill);
   } else {
+    const MCInstrDesc &SMovB32 = TII->get(AMDGPU::S_MOV_B32);
+
     unsigned Rsrc0 = TRI->getSubReg(ScratchRsrcReg, AMDGPU::sub0);
     unsigned Rsrc1 = TRI->getSubReg(ScratchRsrcReg, AMDGPU::sub1);
     unsigned Rsrc2 = TRI->getSubReg(ScratchRsrcReg, AMDGPU::sub2);
     unsigned Rsrc3 = TRI->getSubReg(ScratchRsrcReg, AMDGPU::sub3);
 
     // Use relocations to get the pointer, and setup the other bits manually.
     uint64_t Rsrc23 = TII->getScratchRsrcWords23();
     BuildMI(MBB, I, DL, SMovB32, Rsrc0)