[flang] restrict fir.convert lowering

[SusanTan]

Restrict lowering of fir.convert and exclude core memref types from it. This is in preparation for a lowering that accommodates MemRef dialect.

[llvmbot]

@llvm/pr-subscribers-flang-fir-hlfir

@llvm/pr-subscribers-flang-codegen

Author: Susan Tan (ス-ザン　タン) (SusanTan)

Changes

Restrict lowering of fir.convert and exclude core memref types from it. This is in preparation for a lowering that accommodates MemRef dialect.

---

Full diff: https://github.com/llvm/llvm-project/pull/172117.diff

2 Files Affected:

• (modified) flang/lib/Optimizer/CodeGen/CodeGen.cpp (+10)
• (added) flang/test/Fir/convert-memref-codegen.mlir (+15)

diff --git a/flang/lib/Optimizer/CodeGen/CodeGen.cpp b/flang/lib/Optimizer/CodeGen/CodeGen.cpp
index f96d45d3f6b66..012cddf291efd 100644
--- a/flang/lib/Optimizer/CodeGen/CodeGen.cpp
+++ b/flang/lib/Optimizer/CodeGen/CodeGen.cpp
@@ -816,6 +816,16 @@ struct ConvertOpConversion : public fir::FIROpConversion<fir::ConvertOp> {
                   mlir::ConversionPatternRewriter &rewriter) const override {
     auto fromFirTy = convert.getValue().getType();
     auto toFirTy = convert.getRes().getType();
+
+    // Let more specialized conversions (e.g. FIR to memref
+    // converters) handle fir.convert when either side is a memref. This
+    // avoids interfering with descriptor-based flows such as fir.box /
+    // fir.box_addr and keeps this pattern focused on value conversions.
+    if (mlir::isa<mlir::MemRefType>(fromFirTy) ||
+        mlir::isa<mlir::MemRefType>(toFirTy)) {
+      return mlir::failure();
+    }
+
     auto fromTy = convertType(fromFirTy);
     auto toTy = convertType(toFirTy);
     mlir::Value op0 = adaptor.getOperands()[0];
diff --git a/flang/test/Fir/convert-memref-codegen.mlir b/flang/test/Fir/convert-memref-codegen.mlir
new file mode 100644
index 0000000000000..4496af19e0f67
--- /dev/null
+++ b/flang/test/Fir/convert-memref-codegen.mlir
@@ -0,0 +1,15 @@
+// RUN: not fir-opt --fir-to-llvm-ir="target=x86_64-unknown-linux-gnu" %s -o - 2>&1 | FileCheck %s
+
+// This test ensures that the FIR CodeGen ConvertOpConversion
+// rejects fir.convert when either the source or the destination
+// type is a memref (i.e. it fails to legalize those ops).
+
+module {
+  // CHECK: error: failed to legalize operation 'fir.convert'
+  func.func @memref_to_ref_convert(%arg0: memref<f32>) {
+    %0 = fir.convert %arg0 : (memref<f32>) -> !fir.ref<f32>
+    return
+  }
+}
+
+

[rscottmanley]

Would it be better that the current ConvertOp lowering pattern return failure() instead of aborting with an error? Then another pattern that handles MemRef types could "try"?

[jeanPerier]

LGTM

[jeanPerier]

Nit: no braces for single line if.

[jeanPerier]

Would it be better that the current ConvertOp lowering pattern return failure() instead of aborting with an error? Then another pattern that handles MemRef types could "try"?

Isn't this what this change is doing?