[BACKEND] Cleanup redundant broadcast combine pattern (triton-lang#5167)

Summary of changes:
- Remove `broadcast(cst) -> cst` from the triton-combine pass since it's
redundant with the existing folder.
- Reorder the triton-combine pass to come after the canonicalize pass,
to simplify pattern matching
- Cleanup patterns in triton-reorder-broadcast that called
`Op::canonicalize` in favor of `Op::getCanonicalizationPatterns`.

lib/Dialect/Triton/Transforms/Combine.cpp

@@ -7,7 +7,6 @@
 #include "mlir/Support/LLVM.h"
 #include "mlir/Support/LogicalResult.h"
 #include "mlir/Transforms/GreedyPatternRewriteDriver.h"
-#include "triton/Analysis/Utility.h"
 #include "triton/Dialect/Triton/IR/Dialect.h"
 #include "triton/Dialect/Triton/Transforms/Passes.h"
 
@@ -18,35 +17,7 @@ namespace mlir::triton {
 namespace {
 
 bool isZero(Value val) {
-  if (matchPattern(val, m_Zero()) || matchPattern(val, m_AnyZeroFloat()))
-    return true;
-  // broadcast(constant_0)
-  if (auto bc = val.getDefiningOp<BroadcastOp>()) {
-    if (matchPattern(bc.getSrc(), m_Zero()) ||
-        matchPattern(bc.getSrc(), m_AnyZeroFloat()))
-      return true;
-  }
-  return false;
-}
-
-bool isBroadcastConstantCombinable(Attribute value) {
-  if (auto denseValue = dyn_cast<DenseElementsAttr>(value)) {
-    return denseValue.isSplat();
-  }
-  return isa<FloatAttr, IntegerAttr>(value);
-}
-
-DenseElementsAttr getConstantValue(Builder &builder, Attribute value,
-                                   Value bcast_res) {
-  auto resType = cast<ShapedType>(bcast_res.getType());
-  DenseElementsAttr res;
-  if (auto denseValue = dyn_cast<DenseElementsAttr>(value)) {
-    res =
-        DenseElementsAttr::get(resType, denseValue.getSplatValue<Attribute>());
-  } else {
-    res = DenseElementsAttr::get(resType, value);
-  }
-  return res;
+  return (matchPattern(val, m_Zero()) || matchPattern(val, m_AnyZeroFloat()));
 }
 
 bool isAddPtrOffsetCombinable(Value first, Value second) {
@@ -231,7 +202,6 @@ class CombineOpsPass : public TritonCombineOpsBase<CombineOpsPass> {
     // %}
     patterns.add<CombineSelectMaskedLoadPattern>(context);
     patterns.add<CombineAddPtrPattern>(context);
-    patterns.add<CombineBroadcastConstantPattern>(context);
     patterns.add<CombineBroadcastMulReducePattern>(context);
 
     if (applyPatternsAndFoldGreedily(m, std::move(patterns)).failed())

lib/Dialect/Triton/Transforms/Combine.td

@@ -44,11 +44,4 @@ def CombineAddPtrPattern : Pat<
         (TT_AddPtrOp $ptr, (Arith_AddIOp $idx0, $idx1, DefOverflow)),
         [(Constraint<CPred<"isAddPtrOffsetCombinable($0, $1)">> $idx0, $idx1)]>;
 
-// broadcast(cst) => cst
-def getConstantValue : NativeCodeCall<"getConstantValue($_builder, $0, $1)">;
-def CombineBroadcastConstantPattern : Pat<
-    (TT_BroadcastOp:$bcast_res (Arith_ConstantOp $value)),
-    (Arith_ConstantOp (getConstantValue $value, $bcast_res), (location $bcast_res)),
-    [(Constraint<CPred<"isBroadcastConstantCombinable($0)">> $value)]>;
-
 #endif

lib/Dialect/Triton/Transforms/ReorderBroadcast.cpp

@@ -206,18 +206,6 @@ struct MoveBroadcastAfterElementwisePattern
   }
 };
 
-template <typename OpType>
-class CanonicalizePattern : public OpRewritePattern<OpType> {
-public:
-  explicit CanonicalizePattern(MLIRContext *context)
-      : OpRewritePattern<OpType>(context) {}
-
-  LogicalResult matchAndRewrite(OpType op,
-                                PatternRewriter &rewriter) const override {
-    return OpType::canonicalize(op, rewriter);
-  }
-};
-
 class ReorderBroadcastPass
     : public ::impl::TritonReorderBroadcastBase<ReorderBroadcastPass> {
 public:
@@ -226,8 +214,8 @@ class ReorderBroadcastPass
     RewritePatternSet patterns(context);
     ModuleOp m = getOperation();
 
-    patterns.add<CanonicalizePattern<BroadcastOp>>(context);
-    patterns.add<CanonicalizePattern<ExpandDimsOp>>(context);
+    BroadcastOp::getCanonicalizationPatterns(patterns, context);
+    ExpandDimsOp::getCanonicalizationPatterns(patterns, context);
     // elementwise(broadcast(a)) => broadcast(elementwise(a))
     patterns.add<MoveBroadcastAfterElementwisePattern>(context);
     // elementwise(splat(a), splat(b), ...) => splat(elementwise(a, b, ...))

test/Triton/canonicalize.mlir

@@ -161,3 +161,15 @@ module attributes {"triton_gpu.num-ctas" = 1 : i32, "triton_gpu.num-warps" = 1 :
     tt.return %cst_converted : tensor<32x128xf8E4M3FNUZ, #blocked>
   }
 }  // end module
+
+// -----
+
+// CHECK-LABEL: @fold_broadcast_constant_pattern
+tt.func @fold_broadcast_constant_pattern(%cst : f32) -> tensor<8x2xf32> {
+    // CHECK: %[[cst:.*]] = arith.constant dense<1.000000e+00> : tensor<8x2xf32>
+    %const = arith.constant dense<1.0> : tensor<8x1xf32>
+    %bst_out = tt.broadcast %const : tensor<8x1xf32> -> tensor<8x2xf32>
+
+    // CHECK-NEXT: tt.return %[[cst]] : tensor<8x2xf32>
+    tt.return %bst_out : tensor<8x2xf32>
+}

test/Triton/combine.mlir

@@ -208,16 +208,6 @@ tt.func @test_combine_select_masked_load_fail_pattern(%ptr: tensor<8x!tt.ptr<f32
     tt.return %0, %1, %2 : tensor<8xf32>, tensor<8xf32>, tensor<8xf32>
 }
 
-// CHECK-LABEL: @test_combine_broadcast_constant_pattern
-tt.func @test_combine_broadcast_constant_pattern(%cst : f32) -> tensor<8x2xf32> {
-    // CHECK: %[[cst:.*]] = arith.constant dense<1.000000e+00> : tensor<8x2xf32>
-    %const = arith.constant dense<1.0> : tensor<8x1xf32>
-    %bst_out = tt.broadcast %const : tensor<8x1xf32> -> tensor<8x2xf32>
-
-    // CHECK-NEXT: tt.return %[[cst]] : tensor<8x2xf32>
-    tt.return %bst_out : tensor<8x2xf32>
-}
-
 // CHECK-LABEL: @test_canonicalize_masked_load_pattern
 tt.func @test_canonicalize_masked_load_pattern(%ptr: tensor<8x!tt.ptr<f32>>) -> (tensor<8xf32>, tensor<8xf32>, tensor<8xf32>) {
     %true_mask = arith.constant dense<true> : tensor<8xi1>

third_party/amd/backend/compiler.py

@@ -189,8 +189,8 @@ def make_ttir(mod, metadata, options):
         pm.enable_debug()
         passes.common.add_inliner(pm)
         passes.ttir.add_rewrite_tensor_pointer(pm)
-        passes.ttir.add_combine(pm)
         passes.common.add_canonicalizer(pm)
+        passes.ttir.add_combine(pm)
         passes.ttir.add_reorder_broadcast(pm)
         passes.common.add_cse(pm)
         passes.common.add_licm(pm)

third_party/nvidia/backend/compiler.py

@@ -189,8 +189,8 @@ def make_ttir(mod, metadata, opt):
         pm.enable_debug()
         passes.common.add_inliner(pm)
         passes.ttir.add_rewrite_tensor_pointer(pm)
-        passes.ttir.add_combine(pm)
         passes.common.add_canonicalizer(pm)
+        passes.ttir.add_combine(pm)
         passes.ttir.add_reorder_broadcast(pm)
         passes.common.add_cse(pm)
         passes.common.add_licm(pm)