[BACKEND] Support generic multi-cta convert_layouts (#9317)

Stacked PRs:
 * #9327
 * #9318
 * __->__#9317


--- --- ---

### [BACKEND] Support generic multi-cta convert_layouts


We generalise the swizzling algorithm to work with blocks and generalise
the most of the memory lowerings to support layouts with blocks.

We remove the legacy lowering.

The generic swizzling algorithm for blocks might be fine, but we didn't
try to be super clever. There might be some perf left on the table. We
can look into this at a later point if it becomes relevant.

We also activate multi-cta reductions in the process and test both
there.

TODO: Add some funky tests that just test the `convert_layout`, not the
`convert_layout` within the reduction.
TODO: Check how to perform multiCTA barriers in AMD and perhaps merge
cluster barriers into ttg.barrier, predicate broadcasting blocks, etc.

Author: lezcano

include/triton/Analysis/Utility.h

@@ -419,8 +419,8 @@ template <typename T> class CallGraph {
 // Create a basic DataFlowSolver with constant and dead code analysis included.
 std::unique_ptr<DataFlowSolver> createDataFlowSolver();
 
-bool isCvtWarpSync(const triton::LinearLayout &srcLayout,
-                   const triton::LinearLayout &dstLayout);
+bool isCvtDimSync(const triton::LinearLayout &srcLayout,
+                  const triton::LinearLayout &dstLayout, StringAttr dim);
 
 } // namespace mlir
 

include/triton/Conversion/TritonGPUToLLVM/TargetInfoBase.h

@@ -20,6 +20,8 @@ class TargetInfoBase {
   // target address space
   virtual void barrier(Location loc, RewriterBase &rewriter,
                        triton::gpu::AddrSpace targets) const = 0;
+  // Emit a cluster-level barrier when supported. Defaults to CTA barrier.
+  virtual void clusterBarrier(Location loc, RewriterBase &rewriter) const = 0;
   // Insert a warp syncronization barrier that also guarantees local address
   // space visibility at warp level when supported by the backend.
   // Backends that do not support warp-level barriers should conservatively

include/triton/Conversion/TritonGPUToLLVM/Utility.h

@@ -15,6 +15,8 @@
 #include "triton/Tools/StrUtil.h"
 #include "llvm/ADT/STLExtras.h"
 
+#include <optional>
+
 #define DEBUG_TYPE "ttgpu_to_llvm"
 #define DBGS() (llvm::dbgs() << "[" DEBUG_TYPE "]: ")
 #define LDBG(X) LLVM_DEBUG(DBGS() << X << "\n")
@@ -331,7 +333,7 @@ namespace triton {
 namespace gpu {
 
 std::pair<SmallVector<LocalMemOpTile>, SmallVector<LocalMemOpTile>>
-getSrcDstTiles(const TargetInfoBase &targetInfo, int bitwidth);
+getSrcDstTiles(const TargetInfoBase &targetInfo, int bitwidth, bool crossCTA);
 
 Type getFunctionType(Type resultType, ValueRange operands);
 
@@ -567,17 +569,18 @@ lowerLdStShared(Location loc, MLIRContext *ctx, LinearLayout cvt,
 // calcPaddedOffset is a lambda that takes a base offset (mlir::Value)
 // and computes a new offset (mlir::Value) by applying padding based on
 // shared memory layout.
-SmallVector<Value> lowerLdSt(
-    Location loc, MLIRContext *ctx, LinearLayout cvt,
-    ArrayRef<Value> valsArray, // Input for store, output for load
-    Type llvmElemTy, Value smemBase,
-    ArrayRef<std::pair<unsigned, unsigned>> paddingShifts, Value affineOffset,
-    uint64_t maskSpanAffineOffset, Value laneId, Value warpId,
-    RewriterBase &rewriter, const TargetInfoBase &targetInfo,
-    std::optional<int> maybeMaxVecElems,
-    std::function<SmallVector<Value>(RewriterBase &, Location, ArrayRef<Value>,
-                                     Value, int, VectorType)>
-        lowerInst);
+SmallVector<Value>
+lowerLdSt(Location loc, MLIRContext *ctx, LinearLayout cvt,
+          ArrayRef<Value> valsArray, // Input for store, output for load
+          Type llvmElemTy, Value smemBase,
+          ArrayRef<std::pair<unsigned, unsigned>> paddingShifts,
+          Value affineOffset, uint64_t maskSpanAffineOffset, Value laneId,
+          Value warpId, RewriterBase &rewriter,
+          const TargetInfoBase &targetInfo, std::optional<int> maybeMaxVecElems,
+          std::function<SmallVector<Value>(RewriterBase &, Location,
+                                           ArrayRef<Value>, Value, int,
+                                           VectorType, std::optional<Value>)>
+              lowerInst);
 
 // Lower local_load/local_store via ld.shared/st.shared
 SmallVector<Value>
@@ -619,10 +622,10 @@ void makeAllWarpGroupsIsolatedFromAbove(Operation *op);
 // Set the correct loop annotation on LLVM branch ops.
 void fixUpLoopAnnotation(ModuleOp mod);
 
-void transferWithinBlockSwizzling(triton::gpu::ConvertLayoutOp op, Value src,
-                                  const TargetInfoBase &targetInfo,
-                                  const LLVMTypeConverter *typeConverter,
-                                  RewriterBase &rewriter);
+void transferSwizzlingLocalMem(triton::gpu::ConvertLayoutOp op, Value src,
+                               const TargetInfoBase &targetInfo,
+                               const LLVMTypeConverter *typeConverter,
+                               RewriterBase &rewriter);
 
 SmallVector<Value> inlineRegionImpl(RewriterBase &rewriter, Region &region,
                                     ArrayRef<Value> args,

lib/Analysis/Allocation.cpp

@@ -49,7 +49,11 @@ unsigned getNumScratchElemsSwizzledCvt(const LinearLayout &srcLayout,
   auto smem = gpu::optimalSwizzlingLdSt(srcLayoutNoBroadcast,
                                         dstLayoutNoBroadcast, bitwidth);
   auto reps = smem.getInDimSize(StringAttr::get(ctx, "reps"));
-  return smem.getTotalOutDimSize() / reps;
+  // The smem has the same cta layout as the srcLayout, so we use that instead
+  // We remove the number of elements that are duplicated in the cta layout
+  auto nBlocks = product(triton::gpu::getCTASplitNum(
+      gpu::LinearEncodingAttr::get(ctx, srcLayout)));
+  return smem.getTotalOutDimSize() / (reps * nBlocks);
 }
 
 unsigned getNumScratchElemsSwizzledCvt(RankedTensorType srcTy,

lib/Analysis/Membar.cpp

@@ -324,7 +324,8 @@ void MembarAnalysis::update(Operation *op, BlockInfo *blockInfo,
       auto dstTy = cast<RankedTensorType>(cvt.getType());
       auto srcLayout = triton::gpu::toLinearLayout(srcTy);
       auto dstLayout = triton::gpu::toLinearLayout(dstTy);
-      isWarpSync = mlir::isCvtWarpSync(srcLayout, dstLayout);
+      auto kWarp = StringAttr::get(op->getContext(), "warp");
+      isWarpSync = mlir::isCvtDimSync(srcLayout, dstLayout, kWarp);
     }
 
     if (!curBlockInfo.syncReadSlices.empty() ||

lib/Analysis/Utility.cpp

@@ -1421,17 +1421,23 @@ std::unique_ptr<DataFlowSolver> createDataFlowSolver() {
   return solver;
 }
 
-bool isCvtWarpSync(const triton::LinearLayout &srcLayout,
-                   const triton::LinearLayout &dstLayout) {
-  // We can use warp.sync when the warp dimension in the convert is trival
-  // and there is no broadcasting at a warp level (otherwise reads may be
-  // wrong)
+bool isCvtDimSync(const triton::LinearLayout &srcLayout,
+                  const triton::LinearLayout &dstLayout, StringAttr dim) {
+  // We can use a dimension-level sync when the conversion is trivial over that
+  // dimension and there is no broadcasting over it.
   auto *ctx = srcLayout.getInDimNames().begin()->getContext();
-  auto comp = dstLayout.invertAndCompose(srcLayout);
   auto kWarp = StringAttr::get(ctx, "warp");
-  return comp.isTrivialOver(kWarp) &&
-         srcLayout.getFreeVariableMasks()[kWarp] == 0 &&
-         dstLayout.getFreeVariableMasks()[kWarp] == 0;
+  auto kBlock = StringAttr::get(ctx, "block");
+  assert((dim == kWarp || dim == kBlock) && "expected dim to be warp or block");
+  assert(srcLayout.hasInDim(dim) && dstLayout.hasInDim(dim) &&
+         "expected dim to be present in both layouts");
+  auto parentTrivial = true;
+  if (dim == kWarp) {
+    parentTrivial = isCvtDimSync(srcLayout, dstLayout, kBlock);
+  }
+  auto comp = dstLayout.invertAndCompose(srcLayout);
+  return parentTrivial && comp.isTrivialOver(dim) &&
+         srcLayout.getFreeVariableMasks()[dim] == 0 &&
+         dstLayout.getFreeVariableMasks()[dim] == 0;
 }
-
 } // namespace mlir

lib/Conversion/TritonGPUToLLVM/ConvertLayoutOpToLLVM.cpp

@@ -4,6 +4,8 @@
 #include "triton/Conversion/TritonGPUToLLVM/TargetInfoBase.h"
 #include "triton/Conversion/TritonGPUToLLVM/Utility.h"
 
+#include <optional>
+
 #include "triton/Analysis/Allocation.h"
 #include "triton/Dialect/Triton/IR/Types.h"
 #include "triton/Dialect/Triton/IR/Utility.h"
@@ -45,26 +47,20 @@ struct ConvertLayoutOpConversion
     LinearLayout srcLayout = toLinearLayout(srcTy);
     LinearLayout dstLayout = toLinearLayout(dstTy);
 
-    StringAttr kBlock = str_attr("block");
-    StringAttr kWarp = str_attr("warp");
-    StringAttr kLane = str_attr("lane");
-    StringAttr kRegister = str_attr("register");
+    auto kBlock = str_attr("block");
+    auto kWarp = str_attr("warp");
+    auto kLane = str_attr("lane");
+    auto kRegister = str_attr("register");
 
     auto dims = conversion.getInDimNames();
     bool alwaysUseWarpShuffle = cvtAlwaysUseWarpShuffle(op);
-    assert(!alwaysUseWarpShuffle || (!llvm::is_contained(dims, kBlock) &&
-                                     !llvm::is_contained(dims, kWarp)));
     assert(to_vector(conversion.getInDimNames()) ==
            to_vector(conversion.getOutDimNames()));
-    if (llvm::is_contained(dims, kBlock)) {
-      // Case 1: Transfer between values in different CTAs.
-      //          This requires moving values through distributed shared memory.
-      return rewriter.notifyMatchFailure(
-          op, "NYI: Transfer between different CTAs");
-    } else if (llvm::is_contained(dims, kWarp)) {
-      // Case 2: Transfer between values in the same CTA, in which case we move
-      //         values through shared memory.
-      transferWithinBlockSwizzling(op, adaptor.getSrc(), rewriter);
+    if (llvm::is_contained(dims, kBlock) || llvm::is_contained(dims, kWarp)) {
+      assert(!alwaysUseWarpShuffle);
+      // Transfer between values in the same CTA, or across CTAs. We move values
+      // through (distributed) shared memory.
+      transferSwizzlingLocalMem(op, adaptor.getSrc(), rewriter);
       return success();
     } else if (llvm::is_contained(dims, kLane)) {
       // Case 3. Transfer between values in the same warp, in which case we try
@@ -73,7 +69,7 @@ struct ConvertLayoutOpConversion
       if (cvtNeedsWarpShuffle(srcTy, dstTy) || alwaysUseWarpShuffle)
         return transferWithinWarp(op, adaptor, rewriter);
 
-      transferWithinBlockSwizzling(op, adaptor.getSrc(), rewriter);
+      transferSwizzlingLocalMem(op, adaptor.getSrc(), rewriter);
       return success();
     } else if (llvm::is_contained(dims, kRegister)) {
       // Case 4. Transfer between values in the same thread, in which case we
@@ -93,7 +89,7 @@ struct ConvertLayoutOpConversion
                        ConversionPatternRewriter &rewriter) const {
     MLIRContext *ctx = op.getContext();
     auto loc = op.getLoc();
-    StringAttr kRegister = str_attr("register");
+    auto kRegister = str_attr("register");
     assert(!cvtNeedsSharedMemory(op.getSrc().getType(), op.getType()));
 
     auto srcTy = op.getSrc().getType();
@@ -110,7 +106,7 @@ struct ConvertLayoutOpConversion
     return success();
   }
 
-  SmallVector<Value> transferWithinBlockSwizzlingImpl(
+  SmallVector<Value> transferSwizzlingLocalMemImpl(
       Location loc, ConversionPatternRewriter &rewriter,
       const LinearLayout &srcLayout, const LinearLayout &dstLayout,
       ArrayRef<Value> inVals, Type llvmElemTy, Value smemBase) const {
@@ -126,8 +122,8 @@ struct ConvertLayoutOpConversion
         return b.ptrtoint(llvmElemTyPtr, v).getResult();
       }));
       auto outVals =
-          transferWithinBlockSwizzlingImpl(loc, rewriter, srcLayout, dstLayout,
-                                           newInVals, llvmElemTyPtr, smemBase);
+          transferSwizzlingLocalMemImpl(loc, rewriter, srcLayout, dstLayout,
+                                        newInVals, llvmElemTyPtr, smemBase);
       for (auto &v : outVals) {
         v = b.inttoptr(llvmElemTy, v);
       }
@@ -140,7 +136,7 @@ struct ConvertLayoutOpConversion
       auto i8ElemTy = i8_ty;
       auto newInVals = llvm::to_vector(llvm::map_range(
           inVals, [&](Value v) { return b.zext(i8ElemTy, v).getResult(); }));
-      auto outVals = transferWithinBlockSwizzlingImpl(
+      auto outVals = transferSwizzlingLocalMemImpl(
           loc, rewriter, srcLayout, dstLayout, newInVals, i8ElemTy, smemBase);
       for (auto &v : outVals) {
         v = b.trunc(llvmElemTy, v);
@@ -153,15 +149,15 @@ struct ConvertLayoutOpConversion
     if (!removeBroadcastSrc.isIdentity()) {
       auto prmtSrc = removeBroadcastSrc.apply(srcLayout);
       auto newInVals = removeBroadcastSrc.apply(inVals);
-      return transferWithinBlockSwizzlingImpl(loc, rewriter, prmtSrc, dstLayout,
-                                              newInVals, llvmElemTy, smemBase);
+      return transferSwizzlingLocalMemImpl(loc, rewriter, prmtSrc, dstLayout,
+                                           newInVals, llvmElemTy, smemBase);
     }
 
     // Remove broadcasting in dst
     auto removeBroadcastDst = actionRemoveBroadcastedRegs(dstLayout);
     if (!removeBroadcastDst.isIdentity()) {
       auto prmtDst = removeBroadcastDst.apply(dstLayout);
-      auto outVals = transferWithinBlockSwizzlingImpl(
+      auto outVals = transferSwizzlingLocalMemImpl(
           loc, rewriter, srcLayout, prmtDst, inVals, llvmElemTy, smemBase);
       return broadcastAs(outVals, dstLayout);
     }
@@ -173,6 +169,8 @@ struct ConvertLayoutOpConversion
 
     // Extract reps from smem
     auto kReg = str_attr("register");
+    auto kWarp = str_attr("warp");
+    auto kBlock = str_attr("block");
     auto kReps = str_attr("reps");
     auto nReps = smem.getInDimSize(kReps);
     auto reps = LinearLayout::identity1D(nReps, kReg, kReps);
@@ -194,8 +192,11 @@ struct ConvertLayoutOpConversion
     auto storeCvt = *divideRight(totalStoreCvt, reps);
     auto loadCvt = *divideRight(totalLoadCvt, reps);
     auto kOffset = str_attr("offset");
-    storeCvt = storeCvt.reshapeOuts({{kOffset, storeCvt.getTotalOutDimSize()}});
-    loadCvt = loadCvt.reshapeOuts({{kOffset, loadCvt.getTotalOutDimSize()}});
+    auto nBlock = storeCvt.getInDimSize(kBlock);
+    storeCvt = storeCvt.reshapeOuts(
+        {{kOffset, storeCvt.getTotalOutDimSize() / nBlock}, {kBlock, nBlock}});
+    loadCvt = loadCvt.reshapeOuts(
+        {{kOffset, loadCvt.getTotalOutDimSize() / nBlock}, {kBlock, nBlock}});
 
     auto tileSize = storeCvt.getInDimSize(kReg);
 
@@ -204,28 +205,30 @@ struct ConvertLayoutOpConversion
     auto affineOffset = b.i32_val(0);
     auto maskSpanAffineOffset = 0;
 
-    bool isWarpSync = mlir::isCvtWarpSync(srcLayout, dstLayout);
-    for (int i = 0; i < nReps; ++i) {
-      if (i > 0) {
-        if (isWarpSync) {
-          targetInfo.warpSync(loc, rewriter);
-        } else {
-          targetInfo.barrier(loc, rewriter, triton::gpu::AddrSpace::Local);
-        }
+    bool isWarpSync = mlir::isCvtDimSync(srcLayout, dstLayout, kWarp);
+    bool isBlockSync = mlir::isCvtDimSync(srcLayout, dstLayout, kBlock);
+    auto emitBarrier = [&]() {
+      if (isWarpSync) {
+        targetInfo.warpSync(loc, rewriter);
+      } else if (isBlockSync) {
+        targetInfo.barrier(loc, rewriter, triton::gpu::AddrSpace::Local);
+      } else {
+        targetInfo.clusterBarrier(loc, rewriter);
       }
+    };
+
+    for (int i = 0; i < nReps; ++i) {
+      if (i > 0)
+        emitBarrier();
       auto tileInVals =
           ArrayRef<Value>(permutedInVals).slice(i * tileSize, tileSize);
       // Store
       lowerLdStShared(loc, ctx, storeCvt, tileInVals, llvmElemTy, smemBase,
                       /*paddingShifts=*/{}, affineOffset, maskSpanAffineOffset,
                       rewriter, targetInfo);
-      if (isWarpSync) {
-        targetInfo.warpSync(loc, rewriter);
-      } else {
-        targetInfo.barrier(loc, rewriter, triton::gpu::AddrSpace::Local);
-      }
+      emitBarrier();
       // Load
-      SmallVector<Value> tileOutVals = lowerLdStShared(
+      auto tileOutVals = lowerLdStShared(
           loc, ctx, loadCvt, {}, llvmElemTy, smemBase, /*paddingShifts=*/{},
           affineOffset, maskSpanAffineOffset, rewriter, targetInfo);
       llvm::append_range(outVals, tileOutVals);
@@ -236,30 +239,21 @@ struct ConvertLayoutOpConversion
     return outVals;
   }
 
-  void transferWithinBlockSwizzling(ConvertLayoutOp op, Value src,
-                                    ConversionPatternRewriter &rewriter) const {
+  void transferSwizzlingLocalMem(ConvertLayoutOp op, Value src,
+                                 ConversionPatternRewriter &rewriter) const {
     auto loc = op.getLoc();
     auto *ctx = op.getContext();
     auto srcTy = op.getSrc().getType();
     auto dstTy = op.getType();
 
-    // Remove the kBlock dimension from the layout as it's the identity in the
-    // cvt
     auto srcLayout = toLinearLayout(srcTy);
     auto dstLayout = toLinearLayout(dstTy);
-    auto kReg = str_attr("register");
-    auto kLane = str_attr("lane");
-    auto kWarp = str_attr("warp");
-    srcLayout = srcLayout.sublayout({kReg, kLane, kWarp},
-                                    to_vector(srcLayout.getOutDimNames()));
-    dstLayout = dstLayout.sublayout({kReg, kLane, kWarp},
-                                    to_vector(dstLayout.getOutDimNames()));
 
     auto llvmElemTy = getTypeConverter()->convertType(srcTy.getElementType());
     auto smemBase =
         LLVM::getSharedMemoryBase(loc, rewriter, targetInfo, op.getOperation());
     auto inVals = unpackLLElements(loc, src, rewriter);
-    auto outVals = transferWithinBlockSwizzlingImpl(
+    auto outVals = transferSwizzlingLocalMemImpl(
         loc, rewriter, srcLayout, dstLayout, inVals, llvmElemTy, smemBase);
 
     Value result =
@@ -276,8 +270,8 @@ struct ConvertLayoutOpConversion
     auto b = TritonLLVMOpBuilder(loc, rewriter);
     auto srcTy = op.getSrc().getType();
     auto dstTy = op.getType();
-    StringAttr kReg = str_attr("register");
-    StringAttr kLane = str_attr("lane");
+    auto kReg = str_attr("register");
+    auto kLane = str_attr("lane");
     auto elemTy = getTypeConverter()->convertType(srcTy.getElementType());
     int bitwidth = getIntOrFloatOrPtrBitWidth(elemTy);
 
@@ -434,8 +428,8 @@ struct ConvertLayoutOpConversion
       ArrayRef<TranspositionInfo> mixedTranspositions) const {
     auto *ctx = rewriter.getContext();
     auto b = TritonLLVMOpBuilder(loc, rewriter);
-    StringAttr kReg = str_attr("register");
-    StringAttr kLane = str_attr("lane");
+    auto kReg = str_attr("register");
+    auto kLane = str_attr("lane");
 
     SmallVector<Value> vals(inVals.begin(), inVals.end());
     int m = mixedTranspositions.size();