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Question on emulated bfloat16 scalar code on Phoenix #625

@erwei-xilinx

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@erwei-xilinx

Hi team,

I came across an error when trying to compile a bfloat16 scalar code (x := x ^ 2) on Phoenix, compiled through MLIR-AIR and MLIR-AIE:

LLVM ERROR: unable to legalize instruction: %164:_(<2 x s16>) = G_FMUL %163:_, %163:_ (in function: core_0_2)

Please see the input IRs below:

MLIR-AIE:

    %core_0_2 = aie.core(%tile_0_2) {
      %c32 = arith.constant 32 : index
      %c1 = arith.constant 1 : index
      %c0 = arith.constant 0 : index
      cf.br ^bb1
    ^bb1:  // 2 preds: ^bb0, ^bb1
      aie.use_lock(%lock_0_2_3, AcquireGreaterEqual, 1)
      aie.use_lock(%lock_0_2_2, AcquireGreaterEqual, 1)
      scf.for %arg0 = %c0 to %c32 step %c1 {
        scf.for %arg1 = %c0 to %c32 step %c1 {
          %0 = memref.load %buf0[%arg0, %arg1] : memref<32x32xbf16, 2 : i32>
          %1 = arith.mulf %0, %0 : bf16
          memref.store %1, %buf1[%arg0, %arg1] : memref<32x32xbf16, 2 : i32>
        }
      }
      aie.use_lock(%lock_0_2, Release, 1)
      aie.use_lock(%lock_0_2_4, Release, 1)
      cf.br ^bb1
    } {elf_file = "gelu_seg_core_0_2.elf"}

LLVM IR

module attributes {llvm.target_triple = "aie2"} {
  llvm.mlir.global external @buf0() {addr_space = 0 : i32} : !llvm.array<32 x array<32 x bf16>>
  llvm.mlir.global external @buf1() {addr_space = 0 : i32} : !llvm.array<32 x array<32 x bf16>>
  llvm.mlir.global external @buf2() {addr_space = 0 : i32} : !llvm.array<32 x array<32 x bf16>>
  llvm.mlir.global external @buf3() {addr_space = 0 : i32} : !llvm.array<32 x array<32 x bf16>>
  llvm.func @debug_i32(i32) attributes {sym_visibility = "private"}
  llvm.func @llvm.aie2.put.ms(i32, i32) attributes {sym_visibility = "private"}
  llvm.func @llvm.aie2.get.ss() -> !llvm.struct<(i32, i32)> attributes {sym_visibility = "private"}
  llvm.func @llvm.aie2.mcd.write.vec(vector<16xi32>, i32) attributes {sym_visibility = "private"}
  llvm.func @llvm.aie2.scd.read.vec(i32) -> vector<16xi32> attributes {sym_visibility = "private"}
  llvm.func @llvm.aie2.acquire(i32, i32) attributes {sym_visibility = "private"}
  llvm.func @llvm.aie2.release(i32, i32) attributes {sym_visibility = "private"}
  llvm.mlir.global external @air_channel_3() {addr_space = 0 : i32} : !llvm.array<32 x array<32 x bf16>>
  llvm.mlir.global external @air_channel_0() {addr_space = 0 : i32} : !llvm.array<32 x array<32 x bf16>>
  llvm.func @core_0_2() {
    %0 = llvm.mlir.addressof @buf1 : !llvm.ptr
    %1 = llvm.mlir.addressof @buf0 : !llvm.ptr
    %2 = llvm.mlir.constant(48 : i32) : i32
    %3 = llvm.mlir.constant(51 : i32) : i32
    %4 = llvm.mlir.constant(50 : i32) : i32
    %5 = llvm.mlir.constant(49 : i32) : i32
    %6 = llvm.mlir.constant(1 : i32) : i32
    %7 = llvm.mlir.constant(-1 : i32) : i32
    %8 = llvm.mlir.constant(32 : index) : i64
    %9 = llvm.mlir.constant(1 : index) : i64
    %10 = llvm.mlir.constant(0 : index) : i64
    llvm.br ^bb1
  ^bb1:  // 2 preds: ^bb0, ^bb6
    llvm.call @llvm.aie2.acquire(%5, %7) : (i32, i32) -> ()
    llvm.call @llvm.aie2.acquire(%4, %7) : (i32, i32) -> ()
    llvm.br ^bb2(%10 : i64)
  ^bb2(%11: i64):  // 2 preds: ^bb1, ^bb5
    %12 = llvm.icmp "slt" %11, %8 : i64
    llvm.cond_br %12, ^bb3(%10 : i64), ^bb6
  ^bb3(%13: i64):  // 2 preds: ^bb2, ^bb4
    %14 = llvm.icmp "slt" %13, %8 : i64
    llvm.cond_br %14, ^bb4, ^bb5
  ^bb4:  // pred: ^bb3
    %15 = llvm.getelementptr %1[0, 0, 0] : (!llvm.ptr) -> !llvm.ptr, !llvm.array<32 x array<32 x bf16>>
    %16 = llvm.mul %11, %8 overflow<nsw, nuw> : i64
    %17 = llvm.add %16, %13 overflow<nsw, nuw> : i64
    %18 = llvm.getelementptr inbounds|nuw %15[%17] : (!llvm.ptr, i64) -> !llvm.ptr, bf16
    %19 = llvm.load %18 : !llvm.ptr -> bf16
    %20 = llvm.fmul %19, %19 : bf16
    %21 = llvm.getelementptr %0[0, 0, 0] : (!llvm.ptr) -> !llvm.ptr, !llvm.array<32 x array<32 x bf16>>
    %22 = llvm.getelementptr inbounds|nuw %21[%17] : (!llvm.ptr, i64) -> !llvm.ptr, bf16
    llvm.store %20, %22 : bf16, !llvm.ptr
    %23 = llvm.add %13, %9 : i64
    llvm.br ^bb3(%23 : i64)
  ^bb5:  // pred: ^bb3
    %24 = llvm.add %11, %9 : i64
    llvm.br ^bb2(%24 : i64)
  ^bb6:  // pred: ^bb2
    llvm.call @llvm.aie2.release(%3, %6) : (i32, i32) -> ()
    llvm.call @llvm.aie2.release(%2, %6) : (i32, i32) -> ()
    llvm.br ^bb1
  }
}

Could you please advise on how to get around this issue? Or is there a reason why this code pattern isn't supported?

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