[mlir][arith] Add expansion pattern for ext/trunc of bf16

bf16 has a trivial truncation/extension behavior with F32 that
can be described in elementary arith operations. Include some
expansions to efficiently convert.

Reviewed By: jpienaar

Differential Revision: https://reviews.llvm.org/D147091

diff --git a/mlir/include/mlir/Dialect/Arith/Transforms/Passes.h b/mlir/include/mlir/Dialect/Arith/Transforms/Passes.h
index 257a62a..6d60f8a 100644 (file)
--- a/mlir/include/mlir/Dialect/Arith/Transforms/Passes.h
+++ b/mlir/include/mlir/Dialect/Arith/Transforms/Passes.h
@@ -38,6 +38,9 @@ void populateArithWideIntEmulationPatterns(
 /// Add patterns to expand Arith ceil/floor division ops.
 void populateCeilFloorDivExpandOpsPatterns(RewritePatternSet &patterns);
 
+/// Add patterns to expand Arith bf16 patterns to lower level bitcasts/shifts.
+void populateExpandBFloat16Patterns(RewritePatternSet &patterns);
+
 /// Add patterns to expand Arith ops.
 void populateArithExpandOpsPatterns(RewritePatternSet &patterns);
 

diff --git a/mlir/lib/Dialect/Arith/Transforms/ExpandOps.cpp b/mlir/lib/Dialect/Arith/Transforms/ExpandOps.cpp
index 8f34531..7a62469 100644 (file)
--- a/mlir/lib/Dialect/Arith/Transforms/ExpandOps.cpp
+++ b/mlir/lib/Dialect/Arith/Transforms/ExpandOps.cpp
@@ -10,6 +10,7 @@
 
 #include "mlir/Dialect/Arith/IR/Arith.h"
 #include "mlir/Dialect/Vector/IR/VectorOps.h"
+#include "mlir/IR/ImplicitLocOpBuilder.h"
 #include "mlir/IR/TypeUtilities.h"
 #include "mlir/Transforms/DialectConversion.h"
 
@@ -25,15 +26,13 @@ using namespace mlir;
 /// Create an integer or index constant.
 static Value createConst(Location loc, Type type, int value,
                          PatternRewriter &rewriter) {
-
-  auto elTy = getElementTypeOrSelf(type);
-  auto constantAttr = rewriter.getIntegerAttr(elTy, value);
-
-  if (auto vecTy = llvm::dyn_cast<ShapedType>(type))
+  auto attr = rewriter.getIntegerAttr(getElementTypeOrSelf(type), value);
+  if (auto shapedTy = dyn_cast<ShapedType>(type)) {
     return rewriter.create<arith::ConstantOp>(
-        loc, vecTy, DenseElementsAttr::get(vecTy, constantAttr));
+        loc, DenseElementsAttr::get(shapedTy, attr));
+  }
 
-  return rewriter.create<arith::ConstantOp>(loc, constantAttr);
+  return rewriter.create<arith::ConstantOp>(loc, attr);
 }
 
 namespace {
@@ -187,6 +186,73 @@ public:
   }
 };
 
+struct BFloat16ExtFOpConverter : public OpRewritePattern<arith::ExtFOp> {
+  using OpRewritePattern::OpRewritePattern;
+  LogicalResult matchAndRewrite(arith::ExtFOp op,
+                                PatternRewriter &rewriter) const final {
+    ImplicitLocOpBuilder b(op.getLoc(), rewriter);
+    auto operand = op.getOperand();
+    Type operandTy = operand.getType();
+    Type resultTy = op.getType();
+    Type operandETy = getElementTypeOrSelf(operandTy);
+    Type resultETy = getElementTypeOrSelf(resultTy);
+
+    if (!operandETy.isBF16() || !resultETy.isF32()) {
+      return rewriter.notifyMatchFailure(op, "not a ext of bf16 to f32.");
+    }
+
+    Type i16Ty = b.getI16Type();
+    Type i32Ty = b.getI32Type();
+    if (auto shapedTy = dyn_cast<ShapedType>(operandTy)) {
+      i16Ty = shapedTy.clone(i16Ty);
+      i32Ty = shapedTy.clone(i32Ty);
+    }
+
+    Value bitcast = b.create<arith::BitcastOp>(i16Ty, operand);
+    Value exti = b.create<arith::ExtUIOp>(i32Ty, bitcast);
+
+    Value c16 = createConst(op.getLoc(), i32Ty, 16, rewriter);
+    Value shl = b.create<arith::ShLIOp>(exti, c16);
+    Value result = b.create<arith::BitcastOp>(resultTy, shl);
+
+    rewriter.replaceOp(op, result);
+    return success();
+  }
+};
+
+struct BFloat16TruncFOpConverter : public OpRewritePattern<arith::TruncFOp> {
+  using OpRewritePattern::OpRewritePattern;
+  LogicalResult matchAndRewrite(arith::TruncFOp op,
+                                PatternRewriter &rewriter) const final {
+    ImplicitLocOpBuilder b(op.getLoc(), rewriter);
+    auto operand = op.getOperand();
+    Type operandTy = operand.getType();
+    Type resultTy = op.getType();
+    Type operandETy = getElementTypeOrSelf(operandTy);
+    Type resultETy = getElementTypeOrSelf(resultTy);
+
+    if (!operandETy.isF32() || !resultETy.isBF16()) {
+      return rewriter.notifyMatchFailure(op, "not a trunc of f32 to bf16.");
+    }
+
+    Type i16Ty = b.getI16Type();
+    Type i32Ty = b.getI32Type();
+    if (auto shapedTy = dyn_cast<ShapedType>(operandTy)) {
+      i16Ty = shapedTy.clone(i16Ty);
+      i32Ty = shapedTy.clone(i32Ty);
+    }
+
+    Value bitcast = b.create<arith::BitcastOp>(i32Ty, operand);
+    Value c16 = createConst(op.getLoc(), i32Ty, 16, rewriter);
+    Value shl = b.create<arith::ShRUIOp>(bitcast, c16);
+    Value trunc = b.create<arith::TruncIOp>(i16Ty, shl);
+    Value result = b.create<arith::BitcastOp>(resultTy, trunc);
+
+    rewriter.replaceOp(op, result);
+    return success();
+  }
+};
+
 struct ArithExpandOpsPass
     : public arith::impl::ArithExpandOpsBase<ArithExpandOpsPass> {
   void runOnOperation() override {
@@ -204,6 +270,21 @@ struct ArithExpandOpsPass
       arith::MaxFOp,
       arith::MinFOp
     >();
+
+    target.addDynamicallyLegalOp<arith::ExtFOp>(
+      [](arith::ExtFOp op) {
+        Type inETy = getElementTypeOrSelf(op.getOperand().getType());
+        Type outETy = getElementTypeOrSelf(op.getType());
+        return !(inETy.isBF16() && outETy.isF32());
+      });
+
+    target.addDynamicallyLegalOp<arith::TruncFOp>(
+      [](arith::TruncFOp op)  {
+        Type inETy = getElementTypeOrSelf(op.getOperand().getType());
+        Type outETy = getElementTypeOrSelf(op.getType());
+        return !(inETy.isF32() && outETy.isBF16());
+      });
+
     // clang-format on
     if (failed(applyPartialConversion(getOperation(), target,
                                       std::move(patterns))))
@@ -220,12 +301,19 @@ void mlir::arith::populateCeilFloorDivExpandOpsPatterns(
           patterns.getContext());
 }
 
+void mlir::arith::populateExpandBFloat16Patterns(RewritePatternSet &patterns) {
+  patterns.add<BFloat16ExtFOpConverter, BFloat16TruncFOpConverter>(
+      patterns.getContext());
+}
+
 void mlir::arith::populateArithExpandOpsPatterns(RewritePatternSet &patterns) {
   populateCeilFloorDivExpandOpsPatterns(patterns);
   // clang-format off
   patterns.add<
     MaxMinFOpConverter<MaxFOp, arith::CmpFPredicate::UGT>,
-    MaxMinFOpConverter<MinFOp, arith::CmpFPredicate::ULT>
+    MaxMinFOpConverter<MinFOp, arith::CmpFPredicate::ULT>,
+    BFloat16ExtFOpConverter,
+    BFloat16TruncFOpConverter
    >(patterns.getContext());
   // clang-format on
 }

diff --git a/mlir/test/Dialect/Arith/expand-ops.mlir b/mlir/test/Dialect/Arith/expand-ops.mlir
index 7b7eb40..ba87e29 100644 (file)
--- a/mlir/test/Dialect/Arith/expand-ops.mlir
+++ b/mlir/test/Dialect/Arith/expand-ops.mlir
@@ -215,3 +215,67 @@ func.func @minf(%a: f32, %b: f32) -> f32 {
 // CHECK-NEXT: %[[IS_NAN:.*]] = arith.cmpf uno, %[[RHS]], %[[RHS]] : f32
 // CHECK-NEXT: %[[RESULT:.*]] = arith.select %[[IS_NAN]], %[[RHS]], %[[SELECT]] : f32
 // CHECK-NEXT: return %[[RESULT]] : f32
+
+// -----
+
+func.func @extf_bf16(%arg0 : bf16) -> f32 {
+    %0 = arith.extf %arg0 : bf16 to f32
+    return %0 : f32
+}
+
+// CHECK-LABEL: @extf_bf16
+// CHECK-SAME: %[[ARG0:.+]]: bf16
+// CHECK-DAG: %[[BITCAST:.+]] = arith.bitcast %[[ARG0]] : bf16 to i16
+// CHECK-DAG: %[[EXT:.+]] = arith.extui %[[BITCAST]] : i16 to i32
+// CHECK-DAG: %[[C16:.+]] = arith.constant 16
+// CHECK-DAG: %[[SHLI:.+]] = arith.shli %[[EXT]], %[[C16]]
+// CHECK-DAG: %[[BITCAST:.+]] = arith.bitcast %[[SHLI]] : i32 to f32
+// CHECK: return %[[BITCAST]]
+
+// -----
+
+func.func @extf_vector_bf16(%arg0 : vector<4xbf16>) -> vector<4xf32> {
+    %0 = arith.extf %arg0 : vector<4xbf16> to vector<4xf32>
+    return %0 : vector<4xf32>
+}
+
+// CHECK-LABEL: @extf_vector_bf16
+// CHECK-SAME: %[[ARG0:.+]]: vector<4xbf16>
+// CHECK-DAG: %[[BITCAST:.+]] = arith.bitcast %[[ARG0]] : vector<4xbf16> to vector<4xi16>
+// CHECK-DAG: %[[EXT:.+]] = arith.extui %[[BITCAST]] : vector<4xi16> to vector<4xi32>
+// CHECK-DAG: %[[C16:.+]] = arith.constant dense<16>
+// CHECK-DAG: %[[SHLI:.+]] = arith.shli %[[EXT]], %[[C16]]
+// CHECK-DAG: %[[BITCAST:.+]] = arith.bitcast %[[SHLI]] : vector<4xi32> to vector<4xf32>
+// CHECK: return %[[BITCAST]]
+
+// -----
+
+func.func @truncf_f32(%arg0 : f32) -> bf16 {
+    %0 = arith.truncf %arg0 : f32 to bf16
+    return %0 : bf16
+}
+
+// CHECK-LABEL: @truncf_f32
+// CHECK-SAME: %[[ARG0:.+]]: f32
+// CHECK-DAG: %[[C16:.+]] = arith.constant 16
+// CHECK-DAG: %[[BITCAST:.+]] = arith.bitcast %[[ARG0]] : f32 to i32
+// CHECK-DAG: %[[SHR:.+]] = arith.shrui %[[BITCAST]], %[[C16]]
+// CHECK-DAG: %[[TRUNC:.+]] = arith.trunci %[[SHR]] : i32 to i16
+// CHECK-DAG: %[[BITCAST:.+]] = arith.bitcast %[[TRUNC]] : i16 to bf16
+// CHECK: return %[[BITCAST]] : bf16
+
+// -----
+
+func.func @truncf_vector_f32(%arg0 : vector<4xf32>) -> vector<4xbf16> {
+    %0 = arith.truncf %arg0 : vector<4xf32> to vector<4xbf16>
+    return %0 : vector<4xbf16>
+}
+
+// CHECK-LABEL: @truncf_vector_f32
+// CHECK-SAME: %[[ARG0:.+]]: vector<4xf32>
+// CHECK-DAG: %[[C16:.+]] = arith.constant dense<16>
+// CHECK-DAG: %[[BITCAST:.+]] = arith.bitcast %[[ARG0]] : vector<4xf32> to vector<4xi32>
+// CHECK-DAG: %[[SHR:.+]] = arith.shrui %[[BITCAST]], %[[C16]]
+// CHECK-DAG: %[[TRUNC:.+]] = arith.trunci %[[SHR]] : vector<4xi32> to vector<4xi16>
+// CHECK-DAG: %[[BITCAST:.+]] = arith.bitcast %[[TRUNC]] : vector<4xi16> to vector<4xbf16>
+// CHECK: return %[[BITCAST]] : vector<4xbf16>