Add canonicalizer for ViewOp which folds constants into the ViewOp memref shape and layout map strides and offset.

PiperOrigin-RevId: 279088023

1 files changed, 112 insertions, 0 deletions

diff --git a/mlir/lib/Dialect/StandardOps/Ops.cpp b/mlir/lib/Dialect/StandardOps/Ops.cpp
index 82d4324dff8..60002649a21 100644
--- a/mlir/lib/Dialect/StandardOps/Ops.cpp
+++ b/mlir/lib/Dialect/StandardOps/Ops.cpp
@@ -2419,6 +2419,118 @@ static LogicalResult verify(ViewOp op) {
   return success();
 }
 
+namespace {
+
+struct ViewOpShapeFolder : public OpRewritePattern<ViewOp> {
+  using OpRewritePattern<ViewOp>::OpRewritePattern;
+
+  PatternMatchResult matchAndRewrite(ViewOp viewOp,
+                                     PatternRewriter &rewriter) const override {
+    // Return if none of the operands are constants.
+    if (llvm::none_of(viewOp.getOperands(), [](Value *operand) {
+          return matchPattern(operand, m_ConstantIndex());
+        }))
+      return matchFailure();
+
+    // Get result memref type.
+    auto memrefType = viewOp.getType();
+    if (memrefType.getAffineMaps().size() != 1)
+      return matchFailure();
+    auto map = memrefType.getAffineMaps()[0];
+
+    // Fold any dynamic dim operands which are produced by a constant.
+    SmallVector<int64_t, 4> newShapeConstants;
+    newShapeConstants.reserve(memrefType.getRank());
+    SmallVector<Value *, 4> newOperands;
+    SmallVector<Value *, 4> droppedOperands;
+
+    unsigned dynamicDimPos = 1;
+    unsigned rank = memrefType.getRank();
+    for (unsigned dim = 0, e = rank; dim < e; ++dim) {
+      int64_t dimSize = memrefType.getDimSize(dim);
+      // If this is already static dimension, keep it.
+      if (!ShapedType::isDynamic(dimSize)) {
+        newShapeConstants.push_back(dimSize);
+        continue;
+      }
+      auto *defOp = viewOp.getOperand(dynamicDimPos)->getDefiningOp();
+      if (auto constantIndexOp = dyn_cast_or_null<ConstantIndexOp>(defOp)) {
+        // Dynamic shape dimension will be folded.
+        newShapeConstants.push_back(constantIndexOp.getValue());
+        // Record to check for zero uses later below.
+        droppedOperands.push_back(constantIndexOp);
+      } else {
+        // Dynamic shape dimension not folded; copy operand from old memref.
+        newShapeConstants.push_back(dimSize);
+        newOperands.push_back(viewOp.getOperand(dynamicDimPos));
+      }
+      dynamicDimPos++;
+    }
+
+    // Get offset from old memref view type 'memRefType'.
+    int64_t oldOffset;
+    llvm::SmallVector<int64_t, 4> oldStrides;
+    if (failed(getStridesAndOffset(memrefType, oldStrides, oldOffset)))
+      return matchFailure();
+
+    // Fold dynamic offset operand if it is produced by a constant.
+    auto *dynamicOffset = viewOp.getDynamicOffset();
+    int64_t newOffset = oldOffset;
+    unsigned dynamicOffsetOperandCount = 0;
+    if (dynamicOffset != nullptr) {
+      auto *defOp = dynamicOffset->getDefiningOp();
+      if (auto constantIndexOp = dyn_cast_or_null<ConstantIndexOp>(defOp)) {
+        // Dynamic offset will be folded into the map.
+        newOffset = constantIndexOp.getValue();
+        droppedOperands.push_back(dynamicOffset);
+      } else {
+        // Unable to fold dynamic offset. Add it to 'newOperands' list.
+        newOperands.push_back(dynamicOffset);
+        dynamicOffsetOperandCount = 1;
+      }
+    }
+
+    // Compute new strides based on 'newShapeConstants'.
+    SmallVector<int64_t, 4> newStrides(rank);
+    newStrides[rank - 1] = 1;
+    bool dynamicStrides = false;
+    for (int i = rank - 2; i >= 0; --i) {
+      if (ShapedType::isDynamic(newShapeConstants[i + 1]))
+        dynamicStrides = true;
+      if (dynamicStrides)
+        newStrides[i] = MemRefType::getDynamicStrideOrOffset();
+      else
+        newStrides[i] = newShapeConstants[i + 1] * newStrides[i + 1];
+    }
+
+    // Regenerate strided layout map with 'newStrides' and 'newOffset'.
+    map = makeStridedLinearLayoutMap(newStrides, newOffset,
+                                     rewriter.getContext());
+
+    // Create new memref type with constant folded dims and/or offset/strides.
+    auto newMemRefType =
+        MemRefType::get(newShapeConstants, memrefType.getElementType(), {map},
+                        memrefType.getMemorySpace());
+    assert(static_cast<int64_t>(newOperands.size()) ==
+           dynamicOffsetOperandCount + newMemRefType.getNumDynamicDims());
+
+    // Create new ViewOp.
+    auto newShapeCastOp = rewriter.create<ViewOp>(
+        viewOp.getLoc(), newMemRefType, viewOp.getOperand(0), newOperands);
+    // Insert a cast so we have the same type as the old memref type.
+    rewriter.replaceOpWithNewOp<MemRefCastOp>(droppedOperands, viewOp,
+                                              newShapeCastOp, viewOp.getType());
+    return matchSuccess();
+  }
+};
+
+} // end anonymous namespace
+
+void ViewOp::getCanonicalizationPatterns(OwningRewritePatternList &results,
+                                         MLIRContext *context) {
+  results.insert<ViewOpShapeFolder>(context);
+}
+
 //===----------------------------------------------------------------------===//
 // ZeroExtendIOp
 //===----------------------------------------------------------------------===//