[flang] Support codegen for global procedure pointer

[peixin]

Summary

This supports the codegen for global procedure pointer in BoxedProcedure
pass. Reset the boxproc type.

Depends on D136842.

[jeanPerier]

I think you may need to use updateRootInPlace, otherwise LGTM

flang/lib/Optimizer/CodeGen/BoxedProcedure.cpp

259

I will let @clementval or someone else familiar will MLIR patterns, but I think that if you update an operation in place, you need to use rewriter.updateRootInPlace (or startRootUpdate/finalizeRootUpdate).

[clementval]

flang/lib/Optimizer/CodeGen/BoxedProcedure.cpp

259

@jeanPerier is right. If you don't want weird behavior it is better to use the rewriter to perform the in place update so it is recorded and propagated accordingly.

[peixin]

Thanks @jeanPerier and @clementval . You are right. As mlir/docs/PatternRewriter.md, matchAndRewrite has the restriction of "the root operation is required to either be: updated in-place, replaced, or erased.", and an operation is updated in-place using the transaction-like API (start|cancel|finalize)RootUpdate. Fixed.

[jeanPerier]

Thanks, LGTM

flang/docs/ProcedurePointer.md

 - `flang/lib/Lower/ConvertVariable.cpp:1459`: not yet implemented: procedure pointers
 - `flang/lib/Lower/HostAssociations.cpp:162`: not yet implemented: capture procedure pointer in internal procedure
 - lowering of procedure pointers in ASSOCIATED, NULL, and C_F_PROCPOINTER
 
 Current list of TODOs in code generation:
 
 NOTE: There are any number of possible implementations.
 
-- fir.global for procedure pointers
+BoxedProcedure pass
 
 or
 
 - `flang/lib/Optimizer/CodeGen/TypeConverter.h:64` TODO: BoxProcType type conversion
 - `flang/lib/Optimizer/CodeGen/CodeGen.cpp:2080` not yet implemented: fir.emboxproc codegen
 - `flang/lib/Optimizer/CodeGen/CodeGen.cpp:629` not yet implemented: fir.boxproc_host codegen
 - `flang/lib/Optimizer/CodeGen/CodeGen.cpp:1078` not yet implemented: fir.len_param_index codegen
 - `flang/lib/Optimizer/CodeGen/CodeGen.cpp:3166` not yet implemented: fir.unboxproc codegen
 
 ---
 
 Resources:
 - [1] Fortran standard

flang/lib/Optimizer/CodeGen/BoxedProcedure.cpp

if (options.useThunks) {
                 llvm::ArrayRef<mlir::Value>{tramp});
             rewriter.replaceOpWithNewOp<ConvertOp>(embox, toTy,
                                                    adjustCall.getResult(0));
           } else {
             // Just forward the function as a pointer.
             rewriter.replaceOpWithNewOp<ConvertOp>(embox, toTy,
                                                    embox.getFunc());
           }
+        } else if (auto global = mlir::dyn_cast<GlobalOp>(op)) {
+          auto ty = global.getType();
+          if (typeConverter.needsConversion(ty)) {
+            auto toTy = typeConverter.convertType(ty);
+            global.setType(toTy);
+          }
         } else if (auto mem = mlir::dyn_cast<AllocaOp>(op)) {
           auto ty = mem.getType();
           if (typeConverter.needsConversion(ty)) {
             rewriter.setInsertionPoint(mem);
             auto toTy = typeConverter.convertType(unwrapRefType(ty));
             bool isPinned = mem.getPinned();
             llvm::StringRef uniqName =
                 mem.getUniqName().value_or(llvm::StringRef());

flang/test/Fir/boxproc-2.fir

 // CHECK:           %[[VAL_6:.*]] = fir.field_index solve, !fir.type<_QFtestTmatrixUnboxProc{element:!fir.array<2x2xf32>,solve:() -> ()}>
 // CHECK:           %[[VAL_7:.*]] = fir.coordinate_of %[[VAL_2]], %[[VAL_6]] : (!fir.ref<!fir.type<_QFtestTmatrixUnboxProc{element:!fir.array<2x2xf32>,solve:() -> ()}>>, !fir.field) -> !fir.ref<() -> ()>
 // CHECK:           %[[VAL_8:.*]] = fir.load %[[VAL_7]] : !fir.ref<() -> ()>
 // CHECK:           %[[VAL_9:.*]] = fir.convert %[[VAL_8]] : (() -> ()) -> ((!fir.ref<i32>) -> f32)
 // CHECK:           %[[VAL_10:.*]] = fir.convert %[[VAL_9]] : ((!fir.ref<i32>) -> f32) -> ((!fir.ref<i32>) -> f32)
 // CHECK:           %[[VAL_11:.*]] = fir.call %[[VAL_10]](%[[VAL_1]]) : (!fir.ref<i32>) -> f32
 
 }
+
+// CHECK-LABEL: fir.global internal @ProcedurePointer : (!fir.ref<i32>) -> f32 {
+fir.global internal @ProcedurePointer : !fir.boxproc<(!fir.ref<i32>) -> f32> {
+  %0 = fir.zero_bits (!fir.ref<i32>) -> f32
+  %1 = fir.emboxproc %0 : ((!fir.ref<i32>) -> f32) -> !fir.boxproc<(!fir.ref<i32>) -> f32>
+  fir.has_value %1 : !fir.boxproc<(!fir.ref<i32>) -> f32>
+
+// CHECK: %[[VAL_0:.*]] = fir.zero_bits (!fir.ref<i32>) -> f32
+// CHECK: %[[VAL_1:.*]] = fir.convert %[[VAL_0]] : ((!fir.ref<i32>) -> f32) -> ((!fir.ref<i32>) -> f32)
+// CHECK: fir.has_value %[[VAL_1]] : (!fir.ref<i32>) -> f32
+}
+
+// CHECK-LABEL: func.func @proc_pointer_global() {
+func.func @proc_pointer_global() {
+  %0 = fir.address_of(@ProcedurePointer) : !fir.ref<!fir.boxproc<(!fir.ref<i32>) -> f32>>
+  %1 = fir.load %0 : !fir.ref<!fir.boxproc<(!fir.ref<i32>) -> f32>>
+  return
+
+// CHECK: %[[VAL_0:.*]] = fir.address_of(@ProcedurePointer) : !fir.ref<(!fir.ref<i32>) -> f32>
+// CHECK: %[[VAL_1:.*]] = fir.load %[[VAL_0]] : !fir.ref<(!fir.ref<i32>) -> f32>
+}