[AMD] Support warp-level reduction with DPP (triton-lang#5019)

This commit adds support for warp-level reduction
with DPP instructions, which can improve performance.

See https://gpuopen.com/learn/amd-gcn-assembly-cross-lane-operations/

include/triton/Dialect/Triton/IR/TritonOps.td

@@ -731,6 +731,10 @@ def TT_ReduceOp: TT_Op<"reduce",
       llvm::SmallVector<RankedTensorType> getInputTypes();
       llvm::SmallVector<Type> getElementTypes();
       unsigned getNumOperands();
+
+      // Returns the CombineOp iff this ReduceOp's region contains only
+      // one CombineOp other than the return, or nullptr if not applicable.
+      ::mlir::Operation *getSingleCombiner();
     }];
 }
 

lib/Dialect/Triton/IR/Ops.cpp

@@ -503,6 +503,22 @@ llvm::SmallVector<Type> ReduceOp::getElementTypes() {
   return getElementTypesImpl(this->getOperands());
 }
 
+::mlir::Operation *ReduceOp::getSingleCombiner() {
+  if (getNumOperands() != 1 || getNumResults() != 1)
+    return nullptr;
+  Block *block = &(*getCombineOp().begin());
+  Operation *yield = block->getTerminator();
+  Operation *reduceOp = yield->getOperand(0).getDefiningOp();
+  if (!reduceOp || reduceOp->getNumOperands() != 2 ||
+      reduceOp->getNumResults() != 1)
+    return nullptr;
+  if (reduceOp->getOperand(0) != block->getArgument(0) ||
+      reduceOp->getOperand(1) != block->getArgument(1))
+    return nullptr;
+
+  return reduceOp;
+}
+
 unsigned ReduceOp::getNumOperands() { return this->getOperands().size(); }
 
 //-- ScanOp --

test/Conversion/amd/tritongpu_to_llvm.mlir

@@ -132,3 +132,79 @@ module attributes {"triton_gpu.num-ctas" = 1 : i32, "triton_gpu.num-warps" = 4 :
     tt.return
   }
 }
+
+// -----
+
+#blocked3 = #triton_gpu.blocked<{sizePerThread = [1], threadsPerWarp = [64], warpsPerCTA = [1], order = [0]}>
+module attributes {"triton_gpu.num-ctas" = 1 : i32, "triton_gpu.num-warps" = 1 : i32, "triton_gpu.threads-per-warp" = 64 : i32} {
+  // CHECK-LABEL: reduce_dpp_max
+  tt.func @reduce_dpp_max(%arg0: tensor<64xf32, #blocked3>) {
+    // CHECK: rocdl.update.dpp
+    // CHECK-SAME: with 280, 15, 15, true : f32
+    // CHECK-NEXT: llvm.intr.maxnum
+
+    // CHECK-NEXT: rocdl.update.dpp
+    // CHECK-SAME: with 276, 15, 15, true : f32
+    // CHECK-NEXT: llvm.intr.maxnum
+
+    // CHECK-NEXT: rocdl.update.dpp
+    // CHECK-SAME: with 274, 15, 15, true : f32
+    // CHECK-NEXT: llvm.intr.maxnum
+
+    // CHECK-NEXT: rocdl.update.dpp
+    // CHECK-SAME: with 273, 15, 15, true : f32
+    // CHECK-NEXT: llvm.intr.maxnum
+
+    // CHECK-NEXT: rocdl.update.dpp
+    // CHECK-SAME: with 322, 10, 15, true : f32
+    // CHECK-NEXT: llvm.intr.maxnum
+
+    // CHECK-NEXT: rocdl.update.dpp
+    // CHECK-SAME: with 323, 15, 15, true : f32
+    // CHECK-NEXT: llvm.intr.maxnum
+
+    // CHECK: llvm.amdgcn.readlane
+    %0 = "tt.reduce"(%arg0) <{axis = 0 : i32}> ({
+    ^bb0(%arg1: f32, %arg2: f32):
+      %1 = arith.maxnumf %arg1, %arg2 : f32
+      tt.reduce.return %1 : f32
+    }) : (tensor<64xf32, #blocked3>) -> f32
+    tt.return
+  }
+}
+
+// -----
+
+#blocked4 = #triton_gpu.blocked<{sizePerThread = [1], threadsPerWarp = [64], warpsPerCTA = [1], order = [0]}>
+module attributes {"triton_gpu.num-ctas" = 1 : i32, "triton_gpu.num-warps" = 1 : i32, "triton_gpu.threads-per-warp" = 64 : i32} {
+  // CHECK-LABEL: reduce_xor_max
+  tt.func @reduce_xor_max(%arg0: tensor<32xf32, #blocked4>) {
+    // CHECK: rocdl.ds_swizzle
+    // CHECK: llvm.intr.maxnum
+
+    // CHECK: rocdl.update.dpp
+    // CHECK-SAME: with 280, 15, 12, false : i32
+    // CHECK: rocdl.update.dpp
+    // CHECK-SAME: with 264, 15, 3, false : i32
+    // CHECK: llvm.intr.maxnum
+
+    // CHECK: rocdl.update.dpp
+    // CHECK-SAME: with 276, 15, 10, false : i32
+    // CHECK: rocdl.update.dpp
+    // CHECK-SAME: with 260, 15, 5, false : i32
+    // CHECK: llvm.intr.maxnum
+
+    // CHECK: rocdl.update.dpp
+    // CHECK-SAME: with 78, 15, 15, false : i32
+    // CHECK: llvm.intr.maxnum
+
+    // CHECK: rocdl.update.dpp
+    // CHECK-SAME: with 177, 15, 15, false : i32
+    %0 = "tt.reduce"(%arg0) <{axis = 0 : i32}> ({
+    ^bb0(%arg1: f32, %arg2: f32):
+      %1 = arith.maxnumf %arg1, %arg2 : f32
+      tt.reduce.return %1 : f32
+    }) : (tensor<32xf32, #blocked4>) -> f32
+    tt.return
+  }
+}

third_party/amd/include/TritonAMDGPUToLLVM/TargetUtils.h

@@ -19,6 +19,17 @@ enum class ISAFamily {
 // Deduces the corresponding ISA family for the given target gfx |arch|.
 ISAFamily deduceISAFamily(llvm::StringRef arch);
 
+// Here is a partial definition of DppCtrl enums. For the complete definition,
+// please check:
+// https://github.com/llvm/llvm-project/blob/8c75290/llvm/lib/Target/AMDGPU/SIDefines.h#L939
+enum class DppCtrl : uint32_t {
+  QUAD_PERM_FIRST = 0,
+  ROW_SHL0 = 0x100,
+  ROW_SHR0 = 0x110,
+  BCAST15 = 0x142,
+  BCAST31 = 0x143
+};
+
 } // namespace mlir::triton::AMD
 
 #endif // TRITON_CONVERSION_TRITONGPU_TO_LLVM_TARGETUTILS_H

third_party/amd/lib/TritonAMDGPUToLLVM/TargetInfo.cpp

@@ -5,6 +5,7 @@
 #include "mlir/Dialect/LLVMIR/LLVMDialect.h"
 #include "triton/Conversion/TritonGPUToLLVM/Utility.h"
 
+using mlir::triton::AMD::DppCtrl;
 namespace mlir::triton::AMD {
 
 namespace {
@@ -103,34 +104,207 @@ Value TargetInfo::loadDShared(RewriterBase &rewriter, Location loc, Value ptr,
 
 Value TargetInfo::shuffleXor(RewriterBase &rewriter, Location loc, Value val,
                              int i) const {
-  return LLVM::AMD::shuffleXor(loc, rewriter, val, i);
+  return LLVM::AMD::shuffleXor(loc, rewriter, val, i, getISAFamily());
 }
 
 Value TargetInfo::shuffleUp(RewriterBase &rewriter, Location loc, Value val,
                             int i) const {
-  return LLVM::AMD::shuffleUp(loc, rewriter, val, i);
+  return LLVM::AMD::shuffleUp(loc, rewriter, val, i, getISAFamily());
 }
 
 Value TargetInfo::shuffleIdx(RewriterBase &rewriter, Location loc, Value val,
                              int i) const {
-  return LLVM::AMD::shuffleIdx(loc, rewriter, val, i);
+  return LLVM::AMD::shuffleIdx(loc, rewriter, val, i, getISAFamily());
 }
 
 Value TargetInfo::shuffleIdx(RewriterBase &rewriter, Location loc, Value val,
                              Value i) const {
-  return LLVM::AMD::shuffleIdx(loc, rewriter, val, i);
+  return LLVM::AMD::shuffleIdx(loc, rewriter, val, i, getISAFamily());
 }
 
 Value TargetInfo::programId(RewriterBase &rewriter, Location loc,
                             ModuleOp moduleOp, int axis) const {
   return LLVM::AMD::llGetPid(loc, rewriter, moduleOp, axis);
 }
 
+// Cast and sext values into specific-length int to meet the requirements of
+// instructions like UpdateDpp or readlane if necessary.
+static inline Type castToAndSExtInt(RewriterBase &rewriter, Location loc,
+                                    Value &val, Type fromType,
+                                    unsigned toBits) {
+  unsigned originalBits = fromType.getIntOrFloatBitWidth();
+  Type toType = fromType;
+
+  if (!fromType.isIntOrIndex()) {
+    val = bitcast(val, int_ty(originalBits));
+    toType = int_ty(originalBits);
+  }
+
+  if (originalBits < toBits) {
+    val = sext(int_ty(toBits), val);
+    toType = int_ty(toBits);
+  }
+
+  return toType;
+}
+
+// Trunc the value to specific length and then cast it to given type if
+// necessary. This function is typically used in conjunction with
+// castToAndSExtInt.
+static inline Value truncAndCastFromInt(RewriterBase &rewriter, Location loc,
+                                        Value val, Type valType,
+                                        unsigned fromBits) {
+  unsigned originalBits = valType.getIntOrFloatBitWidth();
+  Value toVal = val;
+
+  if (originalBits < fromBits) {
+    toVal = trunc(int_ty(originalBits), toVal);
+  }
+
+  if (!valType.isIntOrIndex()) {
+    toVal = bitcast(toVal, valType);
+  }
+
+  return toVal;
+}
+
 bool TargetInfo::warpReduce(RewriterBase &rewriter, Location loc,
                             SmallVector<Value> &acc, triton::ReduceOp op,
                             unsigned numLaneToReduce,
                             unsigned interleave) const {
-  return false;
+  if (numLaneToReduce != 64)
+    return false;
+
+  if (auto family = getISAFamily();
+      family != ISAFamily::CDNA3 && family != ISAFamily::CDNA2) {
+    return false;
+  }
+
+  Operation *reduxOp = op.getSingleCombiner();
+  if (!reduxOp)
+    return false;
+
+  auto createDppReduxOpWithBoundCtrl = [&](Type valType, Value &src,
+                                           uint32_t dppCtrl, int rowMask,
+                                           int bankMask) -> Value {
+    // DPP has limited support for data types, so here we need to
+    // cast non-integer types or integer types shorter than 32 bits
+    // to int32, except for fp32.
+    Type actualType = valType;
+    if (!valType.isF32()) {
+      actualType = castToAndSExtInt(rewriter, loc, src, valType, 32);
+    }
+
+    Value dppResult =
+        rewriter
+            .create<ROCDL::DPPUpdateOp>(loc, actualType, src, src,
+                                        rewriter.getI32IntegerAttr(dppCtrl),
+                                        rewriter.getI32IntegerAttr(rowMask),
+                                        rewriter.getI32IntegerAttr(bankMask),
+                                        rewriter.getBoolAttr(true))
+            .getRes();
+
+    if (!valType.isF32()) {
+      src = truncAndCastFromInt(rewriter, loc, src, valType, 32);
+      dppResult = truncAndCastFromInt(rewriter, loc, dppResult, valType, 32);
+    }
+
+    IRMapping mapping;
+    mapping.map(reduxOp->getOperand(0), src);
+    mapping.map(reduxOp->getOperand(1), dppResult);
+    return rewriter.clone(*reduxOp, mapping)->getResult(0);
+  };
+
+  for (int i = 0; i < acc.size(); i++) {
+    Value buf;
+    auto valType = acc[i].getType();
+
+    /*
+      Here's the implementation of full-wavefront reduction using dpp.
+      https://gpuopen.com/learn/amd-gcn-assembly-cross-lane-operations/
+
+      Each step has a v_mov_dpp instruction following the redux op. In
+      some cases, the lower-level compiler could merge them into single
+      instruction. For example, v_mov_dpp + max => v_max_dpp.
+
+      For gfx9, we have 64 threads per warp. These 64 threads are arranged
+      into 4 rows, with each row being 16 threads. Each 16 threads are arranged
+      further into 4 banks, with each bank being 4 threads. Overall it's in a
+      (row, bank, thread) structure. When shuffling, we use row/bank mask to
+      indicate which row/bank to participate. Then modifier like row_shr and
+      row_bcast means exact data movement schemes. In the following
+      instructions, taking row 0 as an example:
+
+      Step 1: Right shift for 8 lanes.
+          lane 8-15 = redux(lane 0-7, lane 8-15)
+
+      Step 2: Right shift for 4 lanes.
+          lane 12-15 = redux(lane 8-11, lane 12-15)
+
+      Step 3: Right shift for 2 lanes.
+          lane 14-15 = redux(lane 12-13, lane 14-15)
+
+      Step 4: Right shift for 1 lane.
+          lane 15 = redux(lane 14, lane 15)
+
+      Step 5: Broadcast lane 15 of each row to all the lanes of its next row.
+          lane 16-31 = redux(lane 15, lane 16-31)
+
+      Step 6: Broadcast lane 31 to lane 32-63.
+          lane 32-63 = redux(lane 31, lane 32-63)
+
+      Now the reduction result is stored in lane 63.
+
+      Step 7: Read the reduction result from lane 63 and broadcast with
+      readlane.
+    */
+
+    const int allRows = 0xf;
+    const int allBanks = 0xf;
+
+    const uint32_t dppCtrlRowShr = static_cast<uint32_t>(DppCtrl::ROW_SHR0);
+
+    // row_shr:8
+    buf = createDppReduxOpWithBoundCtrl(valType, acc[i], 8 + dppCtrlRowShr,
+                                        allRows, allBanks);
+
+    // row_shr:4
+    buf = createDppReduxOpWithBoundCtrl(valType, buf, 4 + dppCtrlRowShr,
+                                        allRows, allBanks);
+
+    // row_shr:2
+    buf = createDppReduxOpWithBoundCtrl(valType, buf, 2 + dppCtrlRowShr,
+                                        allRows, allBanks);
+
+    // row_shr:1
+    buf = createDppReduxOpWithBoundCtrl(valType, buf, 1 + dppCtrlRowShr,
+                                        allRows, allBanks);
+
+    // row_bcast:15 row_mask:0xa
+    buf = createDppReduxOpWithBoundCtrl(
+        valType, buf, static_cast<uint32_t>(DppCtrl::BCAST15), 0xa, allBanks);
+
+    // row_bcast:31
+    buf = createDppReduxOpWithBoundCtrl(valType, buf,
+                                        static_cast<uint32_t>(DppCtrl::BCAST31),
+                                        allRows, allBanks);
+
+    // Similarly, we need to cast data types for readlane instruction.
+    Type actualType = castToAndSExtInt(rewriter, loc, buf, valType, 16);
+
+    // Get reduction result from lane 63
+    std::string intrinsic = "llvm.amdgcn.readlane";
+    Value result =
+        LLVM::createLLVMIntrinsicCallOp(rewriter, loc, intrinsic, actualType,
+                                        ValueRange{buf, i32_val(63)})
+            ->getResult(0);
+
+    result = truncAndCastFromInt(rewriter, loc, result, valType, 16);
+
+    acc[i] = result;
+  }
+
+  return true;
 }
 
 void TargetInfo::printfImpl(Value formatStrStart, int formatStrByteCount,