[llvm] [AMDGPU][GlobalIsel] Add RegBankLegalize rules and lowering for G_AMDGPU_S_BUFFER_LOAD (PR #192480)

[Petar Avramovic via llvm-commits]

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@@ -1205,6 +1272,109 @@ bool RegBankLegalizeHelper::lower(MachineInstr &MI,
     return lowerSplitTo32Select(MI);
   case SplitTo32SExtInReg:
     return lowerSplitTo32SExtInReg(MI);
+  case S_BUF_to_BUF: {
+    Register Dst = MI.getOperand(0).getReg();
+    LLT Ty = MRI.getType(Dst);
+    const RegisterBank *RSrcBank = MRI.getRegBank(MI.getOperand(1).getReg());
+    // FIXME: 96-bit case was widened during legalize. We need to narrow it
+    // back here but don't have an MMO.
+    unsigned LoadSize = Ty.getSizeInBits();
+    int NumLoads = 1;
+    if (LoadSize == 256 || LoadSize == 512) {
+      NumLoads = LoadSize / 128;
+      Ty = Ty.divide(NumLoads);
+    }
+    // Use the alignment to ensure that the required offsets will fit into the
+    // immediate offsets.
+    const Align Alignment = NumLoads > 1 ? Align(16 * NumLoads) : Align(1);
+    MachineFunction &MF = B.getMF();
+    Register SOffset;
+    Register VOffset;
+    int64_t ImmOffset = 0;
+    unsigned MMOOffset = setBufferOffsets(B, MI.getOperand(2).getReg(), VOffset,
+                                          SOffset, ImmOffset, Alignment);
+    // TODO: 96-bit loads were widened to 128-bit results. Shrink the
+    // result if we can, but we need to track an MMO for that.
+    // const unsigned MemSize = (Ty.getSizeInBits() + 7) / 8;
+    const unsigned MemSize = divideCeil(Ty.getSizeInBits(), 8);
+    const DataLayout DL = MF.getDataLayout();
+    Type *IRTy = getTypeForLLT(Ty, MF.getFunction().getContext());
+    const Align MemAlign(DL.getABITypeAlign(IRTy));
+    MachineMemOperand *BaseMMO = MF.getMachineMemOperand(
+        MachinePointerInfo(),
+        MachineMemOperand::MOLoad | MachineMemOperand::MODereferenceable |
+            MachineMemOperand::MOInvariant,
+        MemSize, MemAlign);
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petar-avramovic wrote:

Think that G_AMDGPU_S_BUFFER_LOAD should have MMO, at least from what I tried Legalizer does set MMO and we should use that as a base.
Saw one mir test failing because there was no MMO in mir test, but that should not really be the case

https://github.com/llvm/llvm-project/pull/192480