[Mlir-commits] [mlir] [mlir][EmitC] Expand the MemRefToEmitC pass - Lowering `extract_strided_metadata` (PR #152208)

[Paul Kirth]

================
@@ -288,6 +290,70 @@ struct ConvertStore final : public OpConversionPattern<memref::StoreOp> {
     return success();
   }
 };
+
+struct ConvertExtractStridedMetadata final
+    : public OpConversionPattern<memref::ExtractStridedMetadataOp> {
+  using OpConversionPattern::OpConversionPattern;
+
+  LogicalResult
+  matchAndRewrite(memref::ExtractStridedMetadataOp extractStridedMetadataOp,
+                  OpAdaptor operands,
+                  ConversionPatternRewriter &rewriter) const override {
+    Location loc = extractStridedMetadataOp.getLoc();
+    Value source = extractStridedMetadataOp.getSource();
+
+    MemRefType memrefType = cast<MemRefType>(source.getType());
+    if (!isMemRefTypeLegalForEmitC(memrefType))
+      return rewriter.notifyMatchFailure(
+          loc, "incompatible memref type for EmitC conversion");
+
+    emitc::ConstantOp zeroIndex = rewriter.create<emitc::ConstantOp>(
+        loc, rewriter.getIndexType(), rewriter.getIndexAttr(0));
+    TypedValue<emitc::ArrayType> srcArrayValue =
+        cast<TypedValue<emitc::ArrayType>>(operands.getSource());
+    auto createPointerFromEmitcArray = [loc, &rewriter, &zeroIndex,
+                                        srcArrayValue]() -> emitc::ApplyOp {
+      int64_t rank = srcArrayValue.getType().getRank();
+      llvm::SmallVector<mlir::Value> indices;
+      for (int i = 0; i < rank; ++i) {
+        indices.push_back(zeroIndex);
+      }
+
+      emitc::SubscriptOp subPtr = rewriter.create<emitc::SubscriptOp>(
+          loc, srcArrayValue, mlir::ValueRange(indices));
+      emitc::ApplyOp ptr = rewriter.create<emitc::ApplyOp>(
+          loc,
+          emitc::PointerType::get(srcArrayValue.getType().getElementType()),
+          rewriter.getStringAttr("&"), subPtr);
+
+      return ptr;
+    };
+
+    emitc::ApplyOp srcPtr = createPointerFromEmitcArray();
+    auto [strides, offset] = memrefType.getStridesAndOffset();
+    Value offsetValue = rewriter.create<emitc::ConstantOp>(
+        loc, rewriter.getIndexType(), rewriter.getIndexAttr(offset));
+
+    SmallVector<Value> results;
----------------
ilovepi wrote:

```suggestion
    SmallVector<Value> results;
    unsigned rank = memrefType.getRank();
    results.reserve(2 + 2*rank);
```
You push 2 vals immediately and another 2 items per iteration of the loop, so you know up front how many items you need, and can avoid potentially allocating in the loop below. 

https://github.com/llvm/llvm-project/pull/152208