[AMDGPU] Base getSubRegFromChannel on TableGen data

[critson]

Summary

Generate (at runtime) the table used to drive getSubRegFromChannel,
base on AMDGPUSubRegIdxRanges from TableGen data.
The is a step closer to it being staticly generated by TableGen and
allows getSubRegFromChannel handle all bitwidths in the mean time.

[Flakebi]

Looks good, I have one comment.

llvm/lib/Target/AMDGPU/SIRegisterInfo.cpp

92–93

I think this should be just sizeof(SubRegFromChannelTable).
The previous code used AMDGPU::NoSubRegister instead of NoRegister (both are zero so technically there is no difference).

[arsenm]

LGTM. I think this can remove some of the workarounds in the globalisel insert/extract selection

[arsenm]

llvm/lib/Target/AMDGPU/SIRegisterInfo.cpp

92–93

Yes, this should be NoSubregister

[rampitec]

llvm/lib/Target/AMDGPU/SIRegisterInfo.cpp

45

This could use a comment.

[critson]

Address reviews comments:

• Fix initialiser to use AMDGPU::NoSubRegister and not memset.
• Add comment on mapping array.

[critson]

Having addressed the comments could I get a second quick read before I submit?
Thanks.

llvm/lib/Target/AMDGPU/SIRegisterInfo.cpp

45

Added a detailed comment.

92–93

Agreed, this was meant to be AMDGPU::NoSubRegister.
However I realised this should not be a memset because we are initialising multi-byte elements, so it will fail if AMDGPU::NoSubRegister is not 0.
Switch to an initialisation loop and leave the compiler to appropriately unroll this.

[rampitec]

LGTM

[foad]

llvm/lib/Target/AMDGPU/SIRegisterInfo.cpp

45

It doesn't explain what the 9 means. 9-1 is not a valid index into SubRegFromChannelTable. Also you have a double full stop at the end.

92–93

If you use std::array you can iterate over them with range-based for loops, instead of using array_lengthof.

[critson]

• Use std::array and tidy up initialisation.
• Fix number of rows in table.

llvm/lib/Target/AMDGPU/SIRegisterInfo.cpp

45

Apparently I forgot to increase the array size and this magically did not create any problems. My assertions were also not tight enough to catch this.

[foad]

Looks good. Some nits inline.

llvm/lib/Target/AMDGPU/SIRegisterInfo.cpp

49

uint16_t seems like an odd type to use. unsigned would be more normal, or uint8_t if you want to keep the size down. But it really doesn't matter.

97

You can use .size() here.

195

.size()

[critson]

llvm/lib/Target/AMDGPU/SIRegisterInfo.cpp

49

Currently SubReg is allocated 12 bits in MachineOperand, so needs to be bigger than uint8_t, but fits nicely in uint16_t.

97

It's not a std::array.

195

It's not a std::array.

[foad]

llvm/lib/Target/AMDGPU/SIRegisterInfo.cpp

49

I understand that argument for the ChannelTable but not for the WidthMap.

97

Sorry, I missed that. But it could be :)

[critson]

• Use std::array for map array.

[critson]

llvm/lib/Target/AMDGPU/SIRegisterInfo.cpp

49

Sorry I missed that and agree.

97

I'm a C programmer at heart, so I have an instinctive resistance to these C++ things. I have switched it to std::array.

[Flakebi]

llvm/lib/Target/AMDGPU/SIRegisterInfo.cpp

102

This index should also be Width - 1

llvm/lib/Target/AMDGPU/SIRegisterInfo.h

private:
 
   /// Sub reg indexes for getRegSplitParts.
   /// First index represents subreg size from 1 to 16 DWORDs.
   /// The inner vector is sorted by bit offset.
   /// Provided a register can be fully split with given subregs,
   /// all elements of the inner vector combined give a full lane mask.
   static std::array<std::vector<int16_t>, 16> RegSplitParts;
 
+  // Table representing sub reg of given width and offset.
+  // First index is subreg size: 32, 64, 96, 128, 160, 192, 256, 512.
+  // Second index is 32 different dword offsets.
+  static uint16_t SubRegFromChannelTable[8][32];
+
   void reserveRegisterTuples(BitVector &, MCRegister Reg) const;
 
 public:
   SIRegisterInfo(const GCNSubtarget &ST);
 
   /// \returns the sub reg enum value for the given \p Channel
   /// (e.g. getSubRegFromChannel(0) -> AMDGPU::sub0)
   static unsigned getSubRegFromChannel(unsigned Channel, unsigned NumRegs = 1);

llvm/lib/Target/AMDGPU/SIRegisterInfo.cpp

 
 static cl::opt<bool> EnableSpillSGPRToVGPR(
   "amdgpu-spill-sgpr-to-vgpr",
   cl::desc("Enable spilling VGPRs to SGPRs"),
   cl::ReallyHidden,
   cl::init(true));
 
 std::array<std::vector<int16_t>, 16> SIRegisterInfo::RegSplitParts;
+uint16_t SIRegisterInfo::SubRegFromChannelTable[8][32];
+
+// Map numbers of DWORDs to indexes in SubRegFromChannelTable.
+// Valid indexes are shifted 1, such that a 0 mapping means unsupported.
+// e.g. for 8 DWORDs (256-bit), SubRegFromChannelTableWidthMap[8] = 8,
+//      meaning index 7 in SubRegFromChannelTable..
+static const uint16_t SubRegFromChannelTableWidthMap[17] = {
+    0, 1, 2, 3, 4, 5, 6, 7, 8, 0, 0, 0, 0, 0, 0, 0, 9};
 
 SIRegisterInfo::SIRegisterInfo(const GCNSubtarget &ST)
     : AMDGPUGenRegisterInfo(AMDGPU::PC_REG, ST.getAMDGPUDwarfFlavour()), ST(ST),
       SpillSGPRToVGPR(EnableSpillSGPRToVGPR), isWave32(ST.isWave32()) {
 
   assert(getSubRegIndexLaneMask(AMDGPU::sub0).getAsInteger() == 3 &&
          getSubRegIndexLaneMask(AMDGPU::sub31).getAsInteger() == (3ULL << 62) &&
          (getSubRegIndexLaneMask(AMDGPU::lo16) |
for (unsigned Idx = 1, E = getNumSubRegIndices() - 1; Idx < E; ++Idx) {
       if (Vec.empty()) {
         unsigned MaxNumParts = 1024 / Size; // Maximum register is 1024 bits.
         Vec.resize(MaxNumParts);
       }
       Vec[Pos] = Idx;
     }
   };
 
+  static llvm::once_flag InitializeSubRegFromChannelTableFlag;
+
+  static auto InitializeSubRegFromChannelTableOnce = [this]() {
+    for (unsigned Width = 0; Width < array_lengthof(SubRegFromChannelTable);
+         ++Width)
+      for (unsigned Offset = 0;
+           Offset < array_lengthof(SubRegFromChannelTable[0]); ++Offset)
+        SubRegFromChannelTable[Width][Offset] = AMDGPU::NoSubRegister;
+
+    for (uint16_t Idx = 1; Idx < getNumSubRegIndices(); ++Idx) {
+      unsigned Width = AMDGPUSubRegIdxRanges[Idx].Size / 32;
+      unsigned Offset = AMDGPUSubRegIdxRanges[Idx].Offset / 32;
+      assert(Width < array_lengthof(SubRegFromChannelTableWidthMap));
+      Width = SubRegFromChannelTableWidthMap[Width];
+      if (Width == 0)
+        continue;
+      assert(Offset >= 0 && Offset <= 32);
+      SubRegFromChannelTable[Width - 1][Offset] = Idx;
+    }
+  };
 
   llvm::call_once(InitializeRegSplitPartsFlag, InitializeRegSplitPartsOnce);
+  llvm::call_once(InitializeSubRegFromChannelTableFlag,
+                  InitializeSubRegFromChannelTableOnce);
 }
 
 void SIRegisterInfo::reserveRegisterTuples(BitVector &Reserved,
                                            MCRegister Reg) const {
   MCRegAliasIterator R(Reg, this, true);
 
   for (; R.isValid(); ++R)
     Reserved.set(*R);

 const uint32_t *SIRegisterInfo::getAllVGPRRegMask() const {
   return CSR_AMDGPU_AllVGPRs_RegMask;
 }
 
 const uint32_t *SIRegisterInfo::getAllAllocatableSRegMask() const {
   return CSR_AMDGPU_AllAllocatableSRegs_RegMask;
 }
 
-// FIXME: TableGen should generate something to make this manageable for all
-// register classes. At a minimum we could use the opposite of
-// composeSubRegIndices and go up from the base 32-bit subreg.
 unsigned SIRegisterInfo::getSubRegFromChannel(unsigned Channel,
                                               unsigned NumRegs) {
-  // Table of NumRegs sized pieces at every 32-bit offset.
-  static const uint16_t SubRegFromChannelTable[][32] = {
-      {AMDGPU::sub0,  AMDGPU::sub1,  AMDGPU::sub2,  AMDGPU::sub3,
-       AMDGPU::sub4,  AMDGPU::sub5,  AMDGPU::sub6,  AMDGPU::sub7,
-       AMDGPU::sub8,  AMDGPU::sub9,  AMDGPU::sub10, AMDGPU::sub11,
-       AMDGPU::sub12, AMDGPU::sub13, AMDGPU::sub14, AMDGPU::sub15,
-       AMDGPU::sub16, AMDGPU::sub17, AMDGPU::sub18, AMDGPU::sub19,
-       AMDGPU::sub20, AMDGPU::sub21, AMDGPU::sub22, AMDGPU::sub23,
-       AMDGPU::sub24, AMDGPU::sub25, AMDGPU::sub26, AMDGPU::sub27,
-       AMDGPU::sub28, AMDGPU::sub29, AMDGPU::sub30, AMDGPU::sub31},
-      {AMDGPU::sub0_sub1,   AMDGPU::sub1_sub2,    AMDGPU::sub2_sub3,
-       AMDGPU::sub3_sub4,   AMDGPU::sub4_sub5,    AMDGPU::sub5_sub6,
-       AMDGPU::sub6_sub7,   AMDGPU::sub7_sub8,    AMDGPU::sub8_sub9,
-       AMDGPU::sub9_sub10,  AMDGPU::sub10_sub11,  AMDGPU::sub11_sub12,
-       AMDGPU::sub12_sub13, AMDGPU::sub13_sub14,  AMDGPU::sub14_sub15,
-       AMDGPU::sub15_sub16, AMDGPU::sub16_sub17,  AMDGPU::sub17_sub18,
-       AMDGPU::sub18_sub19, AMDGPU::sub19_sub20,  AMDGPU::sub20_sub21,
-       AMDGPU::sub21_sub22, AMDGPU::sub22_sub23,  AMDGPU::sub23_sub24,
-       AMDGPU::sub24_sub25, AMDGPU::sub25_sub26,  AMDGPU::sub26_sub27,
-       AMDGPU::sub27_sub28, AMDGPU::sub28_sub29,  AMDGPU::sub29_sub30,
-       AMDGPU::sub30_sub31, AMDGPU::NoSubRegister},
-      {AMDGPU::sub0_sub1_sub2,    AMDGPU::sub1_sub2_sub3,
-       AMDGPU::sub2_sub3_sub4,    AMDGPU::sub3_sub4_sub5,
-       AMDGPU::sub4_sub5_sub6,    AMDGPU::sub5_sub6_sub7,
-       AMDGPU::sub6_sub7_sub8,    AMDGPU::sub7_sub8_sub9,
-       AMDGPU::sub8_sub9_sub10,   AMDGPU::sub9_sub10_sub11,
-       AMDGPU::sub10_sub11_sub12, AMDGPU::sub11_sub12_sub13,
-       AMDGPU::sub12_sub13_sub14, AMDGPU::sub13_sub14_sub15,
-       AMDGPU::sub14_sub15_sub16, AMDGPU::sub15_sub16_sub17,
-       AMDGPU::sub16_sub17_sub18, AMDGPU::sub17_sub18_sub19,
-       AMDGPU::sub18_sub19_sub20, AMDGPU::sub19_sub20_sub21,
-       AMDGPU::sub20_sub21_sub22, AMDGPU::sub21_sub22_sub23,
-       AMDGPU::sub22_sub23_sub24, AMDGPU::sub23_sub24_sub25,
-       AMDGPU::sub24_sub25_sub26, AMDGPU::sub25_sub26_sub27,
-       AMDGPU::sub26_sub27_sub28, AMDGPU::sub27_sub28_sub29,
-       AMDGPU::sub28_sub29_sub30, AMDGPU::sub29_sub30_sub31,
-       AMDGPU::NoSubRegister,     AMDGPU::NoSubRegister},
-      {AMDGPU::sub0_sub1_sub2_sub3,     AMDGPU::sub1_sub2_sub3_sub4,
-       AMDGPU::sub2_sub3_sub4_sub5,     AMDGPU::sub3_sub4_sub5_sub6,
-       AMDGPU::sub4_sub5_sub6_sub7,     AMDGPU::sub5_sub6_sub7_sub8,
-       AMDGPU::sub6_sub7_sub8_sub9,     AMDGPU::sub7_sub8_sub9_sub10,
-       AMDGPU::sub8_sub9_sub10_sub11,   AMDGPU::sub9_sub10_sub11_sub12,
-       AMDGPU::sub10_sub11_sub12_sub13, AMDGPU::sub11_sub12_sub13_sub14,
-       AMDGPU::sub12_sub13_sub14_sub15, AMDGPU::sub13_sub14_sub15_sub16,
-       AMDGPU::sub14_sub15_sub16_sub17, AMDGPU::sub15_sub16_sub17_sub18,
-       AMDGPU::sub16_sub17_sub18_sub19, AMDGPU::sub17_sub18_sub19_sub20,
-       AMDGPU::sub18_sub19_sub20_sub21, AMDGPU::sub19_sub20_sub21_sub22,
-       AMDGPU::sub20_sub21_sub22_sub23, AMDGPU::sub21_sub22_sub23_sub24,
-       AMDGPU::sub22_sub23_sub24_sub25, AMDGPU::sub23_sub24_sub25_sub26,
-       AMDGPU::sub24_sub25_sub26_sub27, AMDGPU::sub25_sub26_sub27_sub28,
-       AMDGPU::sub26_sub27_sub28_sub29, AMDGPU::sub27_sub28_sub29_sub30,
-       AMDGPU::sub28_sub29_sub30_sub31, AMDGPU::NoSubRegister,
-       AMDGPU::NoSubRegister,           AMDGPU::NoSubRegister}};
-
-  const unsigned NumRegIndex = NumRegs - 1;
-
-  assert(NumRegIndex < array_lengthof(SubRegFromChannelTable) &&
-         "Not implemented");
+  assert(NumRegs < array_lengthof(SubRegFromChannelTableWidthMap));
+  unsigned NumRegIndex = SubRegFromChannelTableWidthMap[NumRegs];
+  assert(NumRegIndex && "Not implemented");
   assert(Channel < array_lengthof(SubRegFromChannelTable[0]));
-  return SubRegFromChannelTable[NumRegIndex][Channel];
+  return SubRegFromChannelTable[NumRegIndex - 1][Channel];
 }
 
 MCRegister SIRegisterInfo::reservedPrivateSegmentBufferReg(
   const MachineFunction &MF) const {
   unsigned BaseIdx = alignDown(ST.getMaxNumSGPRs(MF), 4) - 4;
   MCRegister BaseReg(AMDGPU::SGPR_32RegClass.getRegister(BaseIdx));
   return getMatchingSuperReg(BaseReg, AMDGPU::sub0, &AMDGPU::SGPR_128RegClass);
 }