[flang] remove support for std::complex value lowering. (#110643)

To avoid ABIs issues, std::complex should be passed/returned by reference to the runtime.

Part of the [RFC to use mlir complex
type](https://discourse.llvm.org/t/rfc-flang-replace-usages-of-fir-complex-by-mlir-complex-type/82292).

Author: jeanPerier

flang/include/flang/Optimizer/Builder/Runtime/RTBuilder.h

@@ -400,17 +400,19 @@ constexpr TypeBuilderFunc getModel<bool &>() {
     return fir::ReferenceType::get(f(context));
   };
 }
-template <>
-constexpr TypeBuilderFunc getModel<std::complex<float>>() {
-  return [](mlir::MLIRContext *context) -> mlir::Type {
-    return mlir::ComplexType::get(mlir::FloatType::getF32(context));
-  };
-}
+
+// getModel<std::complex<T>> are not implemented on purpose.
+// Prefer passing/returning the complex by reference in the runtime to
+// avoid ABI issues.
+// C++ std::complex is not an intrinsic type, and while it is storage
+// compatible with C/Fortran complex type, it follows the struct value passing
+// ABI rule, which may differ from how C complex are passed on some platforms.
+
 template <>
 constexpr TypeBuilderFunc getModel<std::complex<float> &>() {
   return [](mlir::MLIRContext *context) -> mlir::Type {
-    TypeBuilderFunc f{getModel<std::complex<float>>()};
-    return fir::ReferenceType::get(f(context));
+    mlir::Type floatTy = getModel<float>()(context);
+    return fir::ReferenceType::get(mlir::ComplexType::get(floatTy));
   };
 }
 template <>
@@ -422,16 +424,10 @@ constexpr TypeBuilderFunc getModel<const std::complex<float> *>() {
   return getModel<std::complex<float> *>();
 }
 template <>
-constexpr TypeBuilderFunc getModel<std::complex<double>>() {
-  return [](mlir::MLIRContext *context) -> mlir::Type {
-    return mlir::ComplexType::get(mlir::FloatType::getF64(context));
-  };
-}
-template <>
 constexpr TypeBuilderFunc getModel<std::complex<double> &>() {
   return [](mlir::MLIRContext *context) -> mlir::Type {
-    TypeBuilderFunc f{getModel<std::complex<double>>()};
-    return fir::ReferenceType::get(f(context));
+    mlir::Type floatTy = getModel<double>()(context);
+    return fir::ReferenceType::get(mlir::ComplexType::get(floatTy));
   };
 }
 template <>
@@ -521,10 +517,45 @@ REDUCTION_VALUE_OPERATION_MODEL(double)
 REDUCTION_REF_OPERATION_MODEL(long double)
 REDUCTION_VALUE_OPERATION_MODEL(long double)
 
-REDUCTION_REF_OPERATION_MODEL(std::complex<float>)
-REDUCTION_VALUE_OPERATION_MODEL(std::complex<float>)
-REDUCTION_REF_OPERATION_MODEL(std::complex<double>)
-REDUCTION_VALUE_OPERATION_MODEL(std::complex<double>)
+// FIXME: the runtime is not using the correct ABIs when calling complex
+// callbacks. lowering either need to create wrappers or just have an inline
+// implementation for it. https://github.com/llvm/llvm-project/issues/110674
+template <>
+constexpr TypeBuilderFunc
+getModel<Fortran::runtime::ValueReductionOperation<std::complex<float>>>() {
+  return [](mlir::MLIRContext *context) -> mlir::Type {
+    mlir::Type cplx = mlir::ComplexType::get(getModel<float>()(context));
+    auto refTy = fir::ReferenceType::get(cplx);
+    return mlir::FunctionType::get(context, {cplx, cplx}, refTy);
+  };
+}
+template <>
+constexpr TypeBuilderFunc
+getModel<Fortran::runtime::ValueReductionOperation<std::complex<double>>>() {
+  return [](mlir::MLIRContext *context) -> mlir::Type {
+    mlir::Type cplx = mlir::ComplexType::get(getModel<double>()(context));
+    auto refTy = fir::ReferenceType::get(cplx);
+    return mlir::FunctionType::get(context, {cplx, cplx}, refTy);
+  };
+}
+template <>
+constexpr TypeBuilderFunc
+getModel<Fortran::runtime::ReferenceReductionOperation<std::complex<float>>>() {
+  return [](mlir::MLIRContext *context) -> mlir::Type {
+    mlir::Type cplx = mlir::ComplexType::get(getModel<float>()(context));
+    auto refTy = fir::ReferenceType::get(cplx);
+    return mlir::FunctionType::get(context, {refTy, refTy}, refTy);
+  };
+}
+template <>
+constexpr TypeBuilderFunc getModel<
+    Fortran::runtime::ReferenceReductionOperation<std::complex<double>>>() {
+  return [](mlir::MLIRContext *context) -> mlir::Type {
+    mlir::Type cplx = mlir::ComplexType::get(getModel<double>()(context));
+    auto refTy = fir::ReferenceType::get(cplx);
+    return mlir::FunctionType::get(context, {refTy, refTy}, refTy);
+  };
+}
 
 REDUCTION_CHAR_OPERATION_MODEL(char)
 REDUCTION_CHAR_OPERATION_MODEL(char16_t)

flang/unittests/Optimizer/RTBuilder.cpp

@@ -9,6 +9,7 @@
 #include "flang/Optimizer/Builder/Runtime/RTBuilder.h"
 #include "gtest/gtest.h"
 #include "flang/Optimizer/Support/InitFIR.h"
+#include <complex>
 
 // Check that it is possible to make a difference between complex runtime
 // function using C99 complex and C++ std::complex. This is important since