[flang][fir] allow fir.convert from and to !llvm.ptr type

[jeanPerier]

Allow some interaction between LLVM and FIR dialect by allowing conversion between FIR memory types and llvm.ptr type.
This is meant to help experimentation where FIR and LLVM dialect coexists, and is useful to deal with cases where LLVM type makes it early into the MLIR produced by flang, like when inserting LLVM stack intrinsic here:

llvm-project/flang/lib/Optimizer/Transforms/StackReclaim.cpp

Line 57 in 0a00d32

auto stackSaveOp = builder.create<LLVM::StackSaveOp>(loc, voidPtr);

[llvmbot]

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

Author: None (jeanPerier)

Changes

Allow some interaction between LLVM and FIR dialect by allowing conversion between FIR memory types and llvm.ptr type.
This is meant to help experimentation where FIR and LLVM dialect coexists, and is useful to deal with cases where LLVM type makes it early into the MLIR produced by flang, like when inserting LLVM stack intrinsic here:

llvm-project/flang/lib/Optimizer/Transforms/StackReclaim.cpp

Line 57 in 0a00d32

auto stackSaveOp = builder.create<LLVM::StackSaveOp>(loc, voidPtr);

---

Full diff: https://github.com/llvm/llvm-project/pull/106590.diff

3 Files Affected:

• (modified) flang/include/flang/Optimizer/Dialect/FIROps.td (+5-1)
• (modified) flang/lib/Optimizer/Dialect/FIROps.cpp (+1-1)
• (modified) flang/test/Fir/convert.fir (+16)

diff --git a/flang/include/flang/Optimizer/Dialect/FIROps.td b/flang/include/flang/Optimizer/Dialect/FIROps.td
index 2cd202c3623250..68847cfa2cbc25 100644
--- a/flang/include/flang/Optimizer/Dialect/FIROps.td
+++ b/flang/include/flang/Optimizer/Dialect/FIROps.td
@@ -2713,7 +2713,7 @@ def fir_AddrOfOp : fir_OneResultOp<"address_of", [NoMemoryEffect]> {
   let assemblyFormat = "`(` $symbol `)` attr-dict `:` type($resTy)";
 }
 
-def fir_ConvertOp : fir_OneResultOp<"convert", [NoMemoryEffect]> {
+def fir_ConvertOp : fir_SimpleOneResultOp<"convert", [NoMemoryEffect]> {
   let summary = "encapsulates all Fortran entity type conversions";
 
   let description = [{
@@ -2722,6 +2722,9 @@ def fir_ConvertOp : fir_OneResultOp<"convert", [NoMemoryEffect]> {
     type, this instruction is a NOP and may be folded away. This also supports
     integer to pointer conversion and pointer to integer conversion.
 
+    This operation also allows limited interaction between FIR and LLVM
+    dialects by allowing conversion between FIR pointer types and llvm.ptr type.
+
     ```
       %v = ... : i64
       %w = fir.convert %v : (i64) -> i32
@@ -2731,6 +2734,7 @@ def fir_ConvertOp : fir_OneResultOp<"convert", [NoMemoryEffect]> {
   }];
 
   let arguments = (ins AnyType:$value);
+  let results = (outs AnyType:$res);
 
   let assemblyFormat = [{
     $value attr-dict `:` functional-type($value, results)
diff --git a/flang/lib/Optimizer/Dialect/FIROps.cpp b/flang/lib/Optimizer/Dialect/FIROps.cpp
index ce0ae446bb7af8..13a30a358a8660 100644
--- a/flang/lib/Optimizer/Dialect/FIROps.cpp
+++ b/flang/lib/Optimizer/Dialect/FIROps.cpp
@@ -1387,7 +1387,7 @@ bool fir::ConvertOp::isFloatCompatible(mlir::Type ty) {
 bool fir::ConvertOp::isPointerCompatible(mlir::Type ty) {
   return mlir::isa<fir::ReferenceType, fir::PointerType, fir::HeapType,
                    fir::LLVMPointerType, mlir::MemRefType, mlir::FunctionType,
-                   fir::TypeDescType>(ty);
+                   fir::TypeDescType, mlir::LLVM::LLVMPointerType>(ty);
 }
 
 static std::optional<mlir::Type> getVectorElementType(mlir::Type ty) {
diff --git a/flang/test/Fir/convert.fir b/flang/test/Fir/convert.fir
index ef9242ef1d8b41..25a318336aa07d 100644
--- a/flang/test/Fir/convert.fir
+++ b/flang/test/Fir/convert.fir
@@ -11,3 +11,19 @@ func.func @c(%x : !fir.complex<4>) -> !fir.complex<8> {
   %1 = fir.convert %x : (!fir.complex<4>) -> !fir.complex<8>
   return %1 : !fir.complex<8>
 }
+
+func.func @convert_to_llvm_pointer(%x : !fir.llvm_ptr<i32>) -> !llvm.ptr {
+  %0 = fir.convert %x : (!fir.llvm_ptr<i32>) -> !llvm.ptr
+  return %0 : !llvm.ptr
+}
+// CHECK-LABEL: convert_to_llvm_pointer(
+// CHECK-SAME: ptr %[[X:.*]])
+// CHECK-NEXT: ret ptr %[[X]]
+
+func.func @convert_from_llvm_pointer(%x : !llvm.ptr) -> !fir.llvm_ptr<i32> {
+  %0 = fir.convert %x : (!llvm.ptr) -> !fir.llvm_ptr<i32>
+  return %0 : !fir.llvm_ptr<i32>
+}
+// CHECK-LABEL: convert_from_llvm_pointer(
+// CHECK-SAME: ptr %[[X:.*]])
+// CHECK-NEXT: ret ptr %[[X]]

[razvanlupusoru]

Excellent. Makes sense to me!

[clementval]

LGTM