[flang][Evaluate] Restrict ConstantBase constructor overload #138456
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ConstantBase has a constructor that takes a value of any type as an input: template <typename T> ConstantBase(const T &). A derived type Constant<T> is a member of many Expr<T> classes (as an alternative in the member variant). When trying (erroneously) to create Expr<T> from a wrong input, if the specific instance of Expr<T> contains Constant<T>, it's that constructor that will be instantiated, leading to cryptic and unexpected errors. Eliminate the constructor from overload for invalid input values to help produce more meaningful diagnostics.
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@llvm/pr-subscribers-flang-semantics Author: Krzysztof Parzyszek (kparzysz) ChangesConstantBase has a constructor that takes a value of any type as an input: template <typename T> ConstantBase(const T &). A derived type Constant<T> is a member of many Expr<T> classes (as an alternative in the member variant). When trying (erroneously) to create Expr<T> from a wrong input, if the specific instance of Expr<T> contains Constant<T>, it's that constructor that will be instantiated, leading to cryptic and unexpected errors. Eliminate the constructor from overload for invalid input values to help produce more meaningful diagnostics. Full diff: https://github.com/llvm/llvm-project/pull/138456.diff 1 Files Affected:
diff --git a/flang/include/flang/Evaluate/constant.h b/flang/include/flang/Evaluate/constant.h
index 6fc22e3b86aa2..d4c6601c37bca 100644
--- a/flang/include/flang/Evaluate/constant.h
+++ b/flang/include/flang/Evaluate/constant.h
@@ -110,8 +110,12 @@ class ConstantBase : public ConstantBounds {
using Result = RESULT;
using Element = ELEMENT;
- template <typename A>
+ // Constructor for creating ConstantBase from an actual value (i.e.
+ // literals, etc.)
+ template <typename A,
+ typename = std::enable_if_t<std::is_convertible_v<A, Element>>>
ConstantBase(const A &x, Result res = Result{}) : result_{res}, values_{x} {}
+
ConstantBase(ELEMENT &&x, Result res = Result{})
: result_{res}, values_{std::move(x)} {}
ConstantBase(
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ConstantBase has a constructor that takes a value of any type as an input: template ConstantBase(const T &). A derived type Constant is a member of many Expr classes (as an alternative in the member variant).
When trying (erroneously) to create Expr from a wrong input, if the specific instance of Expr contains Constant, it's that constructor that will be instantiated, leading to cryptic and unexpected errors.
Eliminate the constructor from overload for invalid input values to help produce more meaningful diagnostics.