op combine in Triton Dialect: broadcast(cst) -> cst

lib/Conversion/CMakeLists.txt

@@ -1 +1,2 @@
+# add_subdirectory(TritonGPUToLLVM)
 add_subdirectory(TritonToTritonGPU)

lib/Dialect/Triton/Transforms/Combine.cpp

@@ -10,7 +10,7 @@
 
 #include <memory>
 
-// using namespace mlir;
+using namespace mlir;
 
 namespace {
 // dot(a, b, 0) + c => dot(a, b, c)
@@ -114,6 +114,39 @@ public:
     return mlir::failure();
   }
 };
+
+// broadcast(cst) => cst
+// TODO: move this to .td file
+class CombineBroadcastConstantOp : public mlir::RewritePattern {
+public:
+  CombineBroadcastConstantOp(mlir::MLIRContext *context)
+    : mlir::RewritePattern(mlir::RewritePattern::MatchAnyOpTypeTag(), 1,
+                           context) {}
+  
+  LogicalResult matchAndRewrite(Operation *op,
+                                 PatternRewriter &rewriter) const override {
+    if (auto broadcast = llvm::dyn_cast<triton::BroadcastOp>(op)) {
+      if (auto cst = broadcast.src().getDefiningOp<arith::ConstantOp>()) {
+        Attribute value = cst.getValue();
+        Type resType = broadcast.getResult().getType();
+        if (auto denseValue = value.dyn_cast<DenseElementsAttr>()) {
+          if (!denseValue.isSplat())
+            return failure();
+          value = DenseElementsAttr::get(resType, denseValue.getSplatValue<Attribute>());
+        } else {
+          if (!value.isa<FloatAttr, IntegerAttr>())
+            return failure();
+          value = DenseElementsAttr::get(resType, value);
+        }
+        rewriter.replaceOpWithNewOp<arith::ConstantOp>(
+          op, value, resType
+        );
+        return success();
+      }
+    }
+    return failure();
+  }
+};
 } // anonymous namespace
 
 #define GEN_PASS_CLASSES
@@ -129,6 +162,7 @@ public:
     patterns.add<CombineDotOp>(context);
     patterns.add<CombineSelectMaskedLoadOp>(context);
     patterns.add<CombineGEPOp>(context);
+    patterns.add<CombineBroadcastConstantOp>(context);
     // patterns.add<CombineReduceOp>(context);
 
     if (applyPatternsAndFoldGreedily(m, std::move(patterns)).failed())