[Mlir-commits] [mlir] Expand the MemRefToEmitC pass - Lowering `AllocOp` (PR #148257)

[Jaden Angella]

https://github.com/Jaddyen created https://github.com/llvm/llvm-project/pull/148257

This aims to lower `memref.alloc` to `emitc.call_opaque “malloc” `


>From 256dc1144140685f98df8cf33d0e1fdbaa7f1694 Mon Sep 17 00:00:00 2001
From: Jaddyen <ajaden at google.com>
Date: Fri, 11 Jul 2025 00:23:11 +0000
Subject: [PATCH] allocop to emitc malloc

---
 .../MemRefToEmitC/MemRefToEmitC.cpp           | 36 +++++++++++++++++--
 .../MemRefToEmitC/memref-to-emitc.mlir        |  8 +++++
 2 files changed, 42 insertions(+), 2 deletions(-)

diff --git a/mlir/lib/Conversion/MemRefToEmitC/MemRefToEmitC.cpp b/mlir/lib/Conversion/MemRefToEmitC/MemRefToEmitC.cpp
index db244d1d1cac8..382affaff429f 100644
--- a/mlir/lib/Conversion/MemRefToEmitC/MemRefToEmitC.cpp
+++ b/mlir/lib/Conversion/MemRefToEmitC/MemRefToEmitC.cpp
@@ -77,6 +77,38 @@ struct ConvertAlloca final : public OpConversionPattern<memref::AllocaOp> {
   }
 };
 
+struct ConvertAlloc final : public OpConversionPattern<memref::AllocOp> {
+  using OpConversionPattern::OpConversionPattern;
+  LogicalResult
+  matchAndRewrite(memref::AllocOp allocOp, OpAdaptor operands,
+                  ConversionPatternRewriter &rewriter) const override {
+    mlir::Location loc = allocOp.getLoc();
+    auto memrefType = allocOp.getType();
+    if (!memrefType.hasStaticShape())
+      return rewriter.notifyMatchFailure(
+          allocOp.getLoc(), "cannot transform alloc op with dynamic shape");
+
+    int64_t totalSize =
+        memrefType.getNumElements() * memrefType.getElementTypeBitWidth() / 8;
+    auto alignment = allocOp.getAlignment();
+    if (alignment) {
+      int64_t alignVal = alignment.value();
+      totalSize = (totalSize + alignVal - 1) / alignVal * alignVal;
+    }
+    mlir::Value sizeBytes = rewriter.create<emitc::ConstantOp>(
+        loc, rewriter.getIndexType(),
+        rewriter.getIntegerAttr(rewriter.getIndexType(), totalSize));
+    auto mallocPtrType = emitc::PointerType::get(rewriter.getContext(),
+                                                 memrefType.getElementType());
+    auto mallocCall = rewriter.create<emitc::CallOpaqueOp>(
+        loc, mallocPtrType, rewriter.getStringAttr("malloc"),
+        mlir::ValueRange{sizeBytes});
+
+    rewriter.replaceOp(allocOp, mallocCall);
+    return success();
+  }
+};
+
 struct ConvertGlobal final : public OpConversionPattern<memref::GlobalOp> {
   using OpConversionPattern::OpConversionPattern;
 
@@ -222,6 +254,6 @@ void mlir::populateMemRefToEmitCTypeConversion(TypeConverter &typeConverter) {
 
 void mlir::populateMemRefToEmitCConversionPatterns(
     RewritePatternSet &patterns, const TypeConverter &converter) {
-  patterns.add<ConvertAlloca, ConvertGlobal, ConvertGetGlobal, ConvertLoad,
-               ConvertStore>(converter, patterns.getContext());
+  patterns.add<ConvertAlloca, ConvertAlloc, ConvertGlobal, ConvertGetGlobal,
+               ConvertLoad, ConvertStore>(converter, patterns.getContext());
 }
diff --git a/mlir/test/Conversion/MemRefToEmitC/memref-to-emitc.mlir b/mlir/test/Conversion/MemRefToEmitC/memref-to-emitc.mlir
index d37fd1de90add..23e1c20670f8c 100644
--- a/mlir/test/Conversion/MemRefToEmitC/memref-to-emitc.mlir
+++ b/mlir/test/Conversion/MemRefToEmitC/memref-to-emitc.mlir
@@ -8,6 +8,14 @@ func.func @alloca() {
   return
 }
 
+// CHECK-LABEL: alloc()
+func.func @alloc() {
+  // CHECK-NEXT:  %0 = "emitc.constant"() <{value = 3996 : index}> : () -> index
+  // CHECK-NEXT:  %1 = emitc.call_opaque "malloc"(%0) : (index) -> !emitc.ptr<i32>
+  %alloc = memref.alloc() : memref<999xi32>
+  return
+}
+
 // -----
 
 // CHECK-LABEL: memref_store