[flang] correctly deal with bind(c) derived type result ABI (#111969)

Derived type results of BIND(C) function should be returned according
the the C ABI for returning the related C struct type.

This currently did not happen since the abstract-result pass was forcing
the Fortran ABI for all derived type results.
use the bind_c attribute that was added on call/func/dispatch in FIR to
prevent such rewrite in the abstract result pass, and update the
target-rewrite pass to deal with the struct return ABI.

So far, the target specific part of the target-rewrite is only
implemented for X86-64 according to the "System V Application Binary
Interface AMD64 v1", the other targets will hit a TODO, just like for
BIND(C), VALUE derived type arguments.

This intends to deal with #102113.

This is a re-land of #111678 with an extra commit to keep rewriting `type(c_ptr)`
results to `!fir.ref<none>` in the abstract result pass regardless of the ABIs.

Author: jeanPerier

flang/include/flang/Optimizer/CodeGen/Target.h

@@ -126,6 +126,11 @@ class CodeGenSpecifics {
   structArgumentType(mlir::Location loc, fir::RecordType recTy,
                      const Marshalling &previousArguments) const = 0;
 
+  /// Type representation of a `fir.type<T>` type argument when returned by
+  /// value. Such value may need to be converted to a hidden reference argument.
+  virtual Marshalling structReturnType(mlir::Location loc,
+                                       fir::RecordType eleTy) const = 0;
+
   /// Type representation of a `boxchar<n>` type argument when passed by value.
   /// An argument value may need to be passed as a (safe) reference argument.
   ///

flang/include/flang/Optimizer/Dialect/FIROpsSupport.h

@@ -177,6 +177,27 @@ inline mlir::NamedAttribute getAdaptToByRefAttr(Builder &builder) {
 }
 
 bool isDummyArgument(mlir::Value v);
+
+template <fir::FortranProcedureFlagsEnum Flag>
+inline bool hasProcedureAttr(fir::FortranProcedureFlagsEnumAttr flags) {
+  return flags && bitEnumContainsAny(flags.getValue(), Flag);
+}
+
+template <fir::FortranProcedureFlagsEnum Flag>
+inline bool hasProcedureAttr(mlir::Operation *op) {
+  if (auto firCallOp = mlir::dyn_cast<fir::CallOp>(op))
+    return hasProcedureAttr<Flag>(firCallOp.getProcedureAttrsAttr());
+  if (auto firCallOp = mlir::dyn_cast<fir::DispatchOp>(op))
+    return hasProcedureAttr<Flag>(firCallOp.getProcedureAttrsAttr());
+  return hasProcedureAttr<Flag>(
+      op->getAttrOfType<fir::FortranProcedureFlagsEnumAttr>(
+          getFortranProcedureFlagsAttrName()));
+}
+
+inline bool hasBindcAttr(mlir::Operation *op) {
+  return hasProcedureAttr<fir::FortranProcedureFlagsEnum::bind_c>(op);
+}
+
 } // namespace fir
 
 #endif // FORTRAN_OPTIMIZER_DIALECT_FIROPSSUPPORT_H

flang/lib/Optimizer/CodeGen/Target.cpp

@@ -100,6 +100,11 @@ struct GenericTarget : public CodeGenSpecifics {
     TODO(loc, "passing VALUE BIND(C) derived type for this target");
   }
 
+  CodeGenSpecifics::Marshalling
+  structReturnType(mlir::Location loc, fir::RecordType ty) const override {
+    TODO(loc, "returning BIND(C) derived type for this target");
+  }
+
   CodeGenSpecifics::Marshalling
   integerArgumentType(mlir::Location loc,
                       mlir::IntegerType argTy) const override {
@@ -533,14 +538,17 @@ struct TargetX86_64 : public GenericTarget<TargetX86_64> {
   /// When \p recTy is a one field record type that can be passed
   /// like the field on its own, returns the field type. Returns
   /// a null type otherwise.
-  mlir::Type passAsFieldIfOneFieldStruct(fir::RecordType recTy) const {
+  mlir::Type passAsFieldIfOneFieldStruct(fir::RecordType recTy,
+                                         bool allowComplex = false) const {
     auto typeList = recTy.getTypeList();
     if (typeList.size() != 1)
       return {};
     mlir::Type fieldType = typeList[0].second;
     if (mlir::isa<mlir::FloatType, mlir::IntegerType, fir::LogicalType>(
             fieldType))
       return fieldType;
+    if (allowComplex && mlir::isa<mlir::ComplexType>(fieldType))
+      return fieldType;
     if (mlir::isa<fir::CharacterType>(fieldType)) {
       // Only CHARACTER(1) are expected in BIND(C) contexts, which is the only
       // contexts where derived type may be passed in registers.
@@ -593,7 +601,7 @@ struct TargetX86_64 : public GenericTarget<TargetX86_64> {
     postMerge(byteOffset, Lo, Hi);
     if (Lo == ArgClass::Memory || Lo == ArgClass::X87 ||
         Lo == ArgClass::ComplexX87)
-      return passOnTheStack(loc, recTy);
+      return passOnTheStack(loc, recTy, /*isResult=*/false);
     int neededIntRegisters = 0;
     int neededSSERegisters = 0;
     if (Lo == ArgClass::SSE)
@@ -609,7 +617,7 @@ struct TargetX86_64 : public GenericTarget<TargetX86_64> {
     // all in registers or all on the stack).
     if (!hasEnoughRegisters(loc, neededIntRegisters, neededSSERegisters,
                             previousArguments))
-      return passOnTheStack(loc, recTy);
+      return passOnTheStack(loc, recTy, /*isResult=*/false);
 
     if (auto fieldType = passAsFieldIfOneFieldStruct(recTy)) {
       CodeGenSpecifics::Marshalling marshal;
@@ -641,17 +649,65 @@ struct TargetX86_64 : public GenericTarget<TargetX86_64> {
     return marshal;
   }
 
+  CodeGenSpecifics::Marshalling
+  structReturnType(mlir::Location loc, fir::RecordType recTy) const override {
+    std::uint64_t byteOffset = 0;
+    ArgClass Lo, Hi;
+    Lo = Hi = ArgClass::NoClass;
+    byteOffset = classifyStruct(loc, recTy, byteOffset, Lo, Hi);
+    mlir::MLIRContext *context = recTy.getContext();
+    postMerge(byteOffset, Lo, Hi);
+    if (Lo == ArgClass::Memory)
+      return passOnTheStack(loc, recTy, /*isResult=*/true);
+
+    // Note that X87/ComplexX87 are passed in memory, but returned via %st0
+    // %st1 registers. Here, they are returned as fp80 or {fp80, fp80} by
+    // passAsFieldIfOneFieldStruct, and LLVM will use the expected registers.
+
+    // Note that {_Complex long double} is not 100% clear from an ABI
+    // perspective because the aggregate post merger rules say it should be
+    // passed in memory because it is bigger than 2 eight bytes. This has the
+    // funny effect of
+    // {_Complex long double} return to be dealt with differently than
+    // _Complex long double.
+
+    if (auto fieldType =
+            passAsFieldIfOneFieldStruct(recTy, /*allowComplex=*/true)) {
+      if (auto complexType = mlir::dyn_cast<mlir::ComplexType>(fieldType))
+        return complexReturnType(loc, complexType.getElementType());
+      CodeGenSpecifics::Marshalling marshal;
+      marshal.emplace_back(fieldType, AT{});
+      return marshal;
+    }
+
+    if (Hi == ArgClass::NoClass || Hi == ArgClass::SSEUp) {
+      // Return a single integer or floating point argument.
+      mlir::Type lowType = pickLLVMArgType(loc, context, Lo, byteOffset);
+      CodeGenSpecifics::Marshalling marshal;
+      marshal.emplace_back(lowType, AT{});
+      return marshal;
+    }
+    // Will be returned in two different registers. Generate {lowTy, HiTy} for
+    // the LLVM IR result type.
+    CodeGenSpecifics::Marshalling marshal;
+    mlir::Type lowType = pickLLVMArgType(loc, context, Lo, 8u);
+    mlir::Type hiType = pickLLVMArgType(loc, context, Hi, byteOffset - 8u);
+    marshal.emplace_back(mlir::TupleType::get(context, {lowType, hiType}),
+                         AT{});
+    return marshal;
+  }
+
   /// Marshal an argument that must be passed on the stack.
-  CodeGenSpecifics::Marshalling passOnTheStack(mlir::Location loc,
-                                               mlir::Type ty) const {
+  CodeGenSpecifics::Marshalling
+  passOnTheStack(mlir::Location loc, mlir::Type ty, bool isResult) const {
     CodeGenSpecifics::Marshalling marshal;
     auto sizeAndAlign =
         fir::getTypeSizeAndAlignmentOrCrash(loc, ty, getDataLayout(), kindMap);
     // The stack is always 8 byte aligned (note 14 in 3.2.3).
     unsigned short align =
         std::max(sizeAndAlign.second, static_cast<unsigned short>(8));
     marshal.emplace_back(fir::ReferenceType::get(ty),
-                         AT{align, /*byval=*/true, /*sret=*/false});
+                         AT{align, /*byval=*/!isResult, /*sret=*/isResult});
     return marshal;
   }
 };

flang/lib/Optimizer/CodeGen/TargetRewrite.cpp

@@ -142,20 +142,16 @@ class TargetRewrite : public fir::impl::TargetRewritePassBase<TargetRewrite> {
 
   mlir::ModuleOp getModule() { return getOperation(); }
 
-  template <typename A, typename B, typename C>
+  template <typename Ty, typename Callback>
   std::optional<std::function<mlir::Value(mlir::Operation *)>>
-  rewriteCallComplexResultType(
-      mlir::Location loc, A ty, B &newResTys,
-      fir::CodeGenSpecifics::Marshalling &newInTyAndAttrs, C &newOpers,
-      mlir::Value &savedStackPtr) {
-    if (noComplexConversion) {
-      newResTys.push_back(ty);
-      return std::nullopt;
-    }
-    auto m = specifics->complexReturnType(loc, ty.getElementType());
-    // Currently targets mandate COMPLEX is a single aggregate or packed
-    // scalar, including the sret case.
-    assert(m.size() == 1 && "target of complex return not supported");
+  rewriteCallResultType(mlir::Location loc, mlir::Type originalResTy,
+                        Ty &newResTys,
+                        fir::CodeGenSpecifics::Marshalling &newInTyAndAttrs,
+                        Callback &newOpers, mlir::Value &savedStackPtr,
+                        fir::CodeGenSpecifics::Marshalling &m) {
+    // Currently, targets mandate COMPLEX or STRUCT is a single aggregate or
+    // packed scalar, including the sret case.
+    assert(m.size() == 1 && "return type not supported on this target");
     auto resTy = std::get<mlir::Type>(m[0]);
     auto attr = std::get<fir::CodeGenSpecifics::Attributes>(m[0]);
     if (attr.isSRet()) {
@@ -170,7 +166,7 @@ class TargetRewrite : public fir::impl::TargetRewritePassBase<TargetRewrite> {
       newInTyAndAttrs.push_back(m[0]);
       newOpers.push_back(stack);
       return [=](mlir::Operation *) -> mlir::Value {
-        auto memTy = fir::ReferenceType::get(ty);
+        auto memTy = fir::ReferenceType::get(originalResTy);
         auto cast = rewriter->create<fir::ConvertOp>(loc, memTy, stack);
         return rewriter->create<fir::LoadOp>(loc, cast);
       };
@@ -180,11 +176,41 @@ class TargetRewrite : public fir::impl::TargetRewritePassBase<TargetRewrite> {
       // We are going to generate an alloca, so save the stack pointer.
       if (!savedStackPtr)
         savedStackPtr = genStackSave(loc);
-      return this->convertValueInMemory(loc, call->getResult(0), ty,
+      return this->convertValueInMemory(loc, call->getResult(0), originalResTy,
                                         /*inputMayBeBigger=*/true);
     };
   }
 
+  template <typename Ty, typename Callback>
+  std::optional<std::function<mlir::Value(mlir::Operation *)>>
+  rewriteCallComplexResultType(
+      mlir::Location loc, mlir::ComplexType ty, Ty &newResTys,
+      fir::CodeGenSpecifics::Marshalling &newInTyAndAttrs, Callback &newOpers,
+      mlir::Value &savedStackPtr) {
+    if (noComplexConversion) {
+      newResTys.push_back(ty);
+      return std::nullopt;
+    }
+    auto m = specifics->complexReturnType(loc, ty.getElementType());
+    return rewriteCallResultType(loc, ty, newResTys, newInTyAndAttrs, newOpers,
+                                 savedStackPtr, m);
+  }
+
+  template <typename Ty, typename Callback>
+  std::optional<std::function<mlir::Value(mlir::Operation *)>>
+  rewriteCallStructResultType(
+      mlir::Location loc, fir::RecordType recTy, Ty &newResTys,
+      fir::CodeGenSpecifics::Marshalling &newInTyAndAttrs, Callback &newOpers,
+      mlir::Value &savedStackPtr) {
+    if (noStructConversion) {
+      newResTys.push_back(recTy);
+      return std::nullopt;
+    }
+    auto m = specifics->structReturnType(loc, recTy);
+    return rewriteCallResultType(loc, recTy, newResTys, newInTyAndAttrs,
+                                 newOpers, savedStackPtr, m);
+  }
+
   void passArgumentOnStackOrWithNewType(
       mlir::Location loc, fir::CodeGenSpecifics::TypeAndAttr newTypeAndAttr,
       mlir::Type oldType, mlir::Value oper,
@@ -356,6 +382,11 @@ class TargetRewrite : public fir::impl::TargetRewritePassBase<TargetRewrite> {
                                                 newInTyAndAttrs, newOpers,
                                                 savedStackPtr);
           })
+          .template Case<fir::RecordType>([&](fir::RecordType recTy) {
+            wrap = rewriteCallStructResultType(loc, recTy, newResTys,
+                                               newInTyAndAttrs, newOpers,
+                                               savedStackPtr);
+          })
           .Default([&](mlir::Type ty) { newResTys.push_back(ty); });
     } else if (fnTy.getResults().size() > 1) {
       TODO(loc, "multiple results not supported yet");
@@ -562,6 +593,24 @@ class TargetRewrite : public fir::impl::TargetRewritePassBase<TargetRewrite> {
     }
   }
 
+  template <typename Ty>
+  void
+  lowerStructSignatureRes(mlir::Location loc, fir::RecordType recTy,
+                          Ty &newResTys,
+                          fir::CodeGenSpecifics::Marshalling &newInTyAndAttrs) {
+    if (noComplexConversion) {
+      newResTys.push_back(recTy);
+      return;
+    } else {
+      for (auto &tup : specifics->structReturnType(loc, recTy)) {
+        if (std::get<fir::CodeGenSpecifics::Attributes>(tup).isSRet())
+          newInTyAndAttrs.push_back(tup);
+        else
+          newResTys.push_back(std::get<mlir::Type>(tup));
+      }
+    }
+  }
+
   void
   lowerStructSignatureArg(mlir::Location loc, fir::RecordType recTy,
                           fir::CodeGenSpecifics::Marshalling &newInTyAndAttrs) {
@@ -595,6 +644,9 @@ class TargetRewrite : public fir::impl::TargetRewritePassBase<TargetRewrite> {
           .Case<mlir::ComplexType>([&](mlir::ComplexType ty) {
             lowerComplexSignatureRes(loc, ty, newResTys, newInTyAndAttrs);
           })
+          .Case<fir::RecordType>([&](fir::RecordType ty) {
+            lowerStructSignatureRes(loc, ty, newResTys, newInTyAndAttrs);
+          })
           .Default([&](mlir::Type ty) { newResTys.push_back(ty); });
     }
     llvm::SmallVector<mlir::Type> trailingInTys;
@@ -696,7 +748,8 @@ class TargetRewrite : public fir::impl::TargetRewritePassBase<TargetRewrite> {
     for (auto ty : func.getResults())
       if ((mlir::isa<fir::BoxCharType>(ty) && !noCharacterConversion) ||
           (fir::isa_complex(ty) && !noComplexConversion) ||
-          (mlir::isa<mlir::IntegerType>(ty) && hasCCallingConv)) {
+          (mlir::isa<mlir::IntegerType>(ty) && hasCCallingConv) ||
+          (mlir::isa<fir::RecordType>(ty) && !noStructConversion)) {
         LLVM_DEBUG(llvm::dbgs() << "rewrite " << signature << " for target\n");
         return false;
       }
@@ -770,6 +823,9 @@ class TargetRewrite : public fir::impl::TargetRewritePassBase<TargetRewrite> {
                                                 rewriter->getUnitAttr()));
             newResTys.push_back(retTy);
           })
+          .Case<fir::RecordType>([&](fir::RecordType recTy) {
+            doStructReturn(func, recTy, newResTys, newInTyAndAttrs, fixups);
+          })
           .Default([&](mlir::Type ty) { newResTys.push_back(ty); });
 
     // Saved potential shift in argument. Handling of result can add arguments
@@ -1062,21 +1118,12 @@ class TargetRewrite : public fir::impl::TargetRewritePassBase<TargetRewrite> {
     return false;
   }
 
-  /// Convert a complex return value. This can involve converting the return
-  /// value to a "hidden" first argument or packing the complex into a wide
-  /// GPR.
   template <typename Ty, typename FIXUPS>
-  void doComplexReturn(mlir::func::FuncOp func, mlir::ComplexType cmplx,
-                       Ty &newResTys,
-                       fir::CodeGenSpecifics::Marshalling &newInTyAndAttrs,
-                       FIXUPS &fixups) {
-    if (noComplexConversion) {
-      newResTys.push_back(cmplx);
-      return;
-    }
-    auto m =
-        specifics->complexReturnType(func.getLoc(), cmplx.getElementType());
-    assert(m.size() == 1);
+  void doReturn(mlir::func::FuncOp func, Ty &newResTys,
+                fir::CodeGenSpecifics::Marshalling &newInTyAndAttrs,
+                FIXUPS &fixups, fir::CodeGenSpecifics::Marshalling &m) {
+    assert(m.size() == 1 &&
+           "expect result to be turned into single argument or result so far");
     auto &tup = m[0];
     auto attr = std::get<fir::CodeGenSpecifics::Attributes>(tup);
     auto argTy = std::get<mlir::Type>(tup);
@@ -1117,6 +1164,36 @@ class TargetRewrite : public fir::impl::TargetRewritePassBase<TargetRewrite> {
     newResTys.push_back(argTy);
   }
 
+  /// Convert a complex return value. This can involve converting the return
+  /// value to a "hidden" first argument or packing the complex into a wide
+  /// GPR.
+  template <typename Ty, typename FIXUPS>
+  void doComplexReturn(mlir::func::FuncOp func, mlir::ComplexType cmplx,
+                       Ty &newResTys,
+                       fir::CodeGenSpecifics::Marshalling &newInTyAndAttrs,
+                       FIXUPS &fixups) {
+    if (noComplexConversion) {
+      newResTys.push_back(cmplx);
+      return;
+    }
+    auto m =
+        specifics->complexReturnType(func.getLoc(), cmplx.getElementType());
+    doReturn(func, newResTys, newInTyAndAttrs, fixups, m);
+  }
+
+  template <typename Ty, typename FIXUPS>
+  void doStructReturn(mlir::func::FuncOp func, fir::RecordType recTy,
+                      Ty &newResTys,
+                      fir::CodeGenSpecifics::Marshalling &newInTyAndAttrs,
+                      FIXUPS &fixups) {
+    if (noStructConversion) {
+      newResTys.push_back(recTy);
+      return;
+    }
+    auto m = specifics->structReturnType(func.getLoc(), recTy);
+    doReturn(func, newResTys, newInTyAndAttrs, fixups, m);
+  }
+
   template <typename FIXUPS>
   void
   createFuncOpArgFixups(mlir::func::FuncOp func,