[flang-commits] [flang] [flang] To issue error message for unsupported usage of vector type. (PR #215248)

[Daniel Chen via flang-commits]

https://github.com/DanielCChen created https://github.com/llvm/llvm-project/pull/215248

As discussed in PR #214219, we don't plan to support any usage that requires runtime descriptor for vector type object.
Flang has already disallowed ALLOCATABLE, POINTER, ASSUMED-SHAPE and ASSUMED-RANK for vector types.
The test reducer posted by @eugeneepshteyn should also be flagged by the compiler as an error.
This PR is to add semantic check for that case. It covers
1. ALLOCATE statement where SOURCE= or MOLD= has a vector type object.
2. Auto-allocation intrinsic assignment where the RHS is a vector type object.
3. A vector type object being used as an argument of SAME_TYPE_AS or EXTENDs_TYPE_OF.

>From f81a25543785236b63aedf67000935a6969fc29c Mon Sep 17 00:00:00 2001
From: Daniel Chen <cdchen at ca.ibm.com>
Date: Mon, 10 Aug 2026 07:16:59 -0400
Subject: [PATCH] [flang] To issue error message for unsupported usage of
 vector type.

---
 flang/lib/Evaluate/tools.cpp                  |  3 +-
 flang/lib/Semantics/check-allocate.cpp        |  6 +++
 flang/lib/Semantics/expression.cpp            | 10 +++++
 .../PowerPC/ppc-vector-poly-checks.f90        | 45 +++++++++++++++++++
 4 files changed, 63 insertions(+), 1 deletion(-)
 create mode 100644 flang/test/Semantics/PowerPC/ppc-vector-poly-checks.f90

diff --git a/flang/lib/Evaluate/tools.cpp b/flang/lib/Evaluate/tools.cpp
index 34deaaea289c1..a1536194242f4 100644
--- a/flang/lib/Evaluate/tools.cpp
+++ b/flang/lib/Evaluate/tools.cpp
@@ -2761,7 +2761,8 @@ bool IsLenTypeParameter(const Symbol &symbol) {
 }
 
 bool IsExtensibleType(const DerivedTypeSpec *derived) {
-  return !IsSequenceOrBindCType(derived) && !IsIsoCType(derived);
+  return !IsSequenceOrBindCType(derived) && !IsIsoCType(derived) &&
+      !(derived && derived->IsVectorType());
 }
 
 bool IsSequenceOrBindCType(const DerivedTypeSpec *derived) {
diff --git a/flang/lib/Semantics/check-allocate.cpp b/flang/lib/Semantics/check-allocate.cpp
index 7f099d51221c0..2ac242abd5788 100644
--- a/flang/lib/Semantics/check-allocate.cpp
+++ b/flang/lib/Semantics/check-allocate.cpp
@@ -238,6 +238,12 @@ static std::optional<AllocateCheckerInfo> CheckAllocateOptions(
       info.sourceExprLoc = parserSourceExpr->source;
       if (const DerivedTypeSpec *
           derived{evaluate::GetDerivedTypeSpec(info.sourceExprType)}) {
+        if (derived->IsVectorType()) {
+          context.Say(at,
+              "SOURCE or MOLD expression must not be a vector type '%s'"_err_en_US,
+              info.sourceExprType.value().AsFortran());
+          return std::nullopt;
+        }
         // C949
         if (auto it{FindCoarrayUltimateComponent(*derived)}) {
           context
diff --git a/flang/lib/Semantics/expression.cpp b/flang/lib/Semantics/expression.cpp
index fc57cc43e981c..1cc3715330b64 100644
--- a/flang/lib/Semantics/expression.cpp
+++ b/flang/lib/Semantics/expression.cpp
@@ -3852,6 +3852,16 @@ const Assignment *ExpressionAnalyzer::Analyze(const parser::AssignmentStmt &x) {
               Warn(common::UsageWarning::IgnoredNoReallocateLHS,
                   "-fno-realloc-lhs is ignored for assignment to polymorphic allocatable"_warn_en_US);
             }
+            const Expr<SomeType> &rhs{analyzer.GetExpr(1)};
+            if (auto rhsType{rhs.GetType()}) {
+              if (const auto *rhsDerived{GetDerivedTypeSpec(*rhsType)}) {
+                if (rhsDerived->IsVectorType()) {
+                  Say(rhsExpr.source,
+                      "Vector type '%s' may not be used as the right-hand side of a polymorphic intrinsic assignment"_err_en_US,
+                      rhsType->AsFortran());
+                }
+              }
+            }
           }
           if (auto *derived{GetDerivedTypeSpec(*dyType)}) {
             if (auto iter{FindAllocatableUltimateComponent(*derived)}) {
diff --git a/flang/test/Semantics/PowerPC/ppc-vector-poly-checks.f90 b/flang/test/Semantics/PowerPC/ppc-vector-poly-checks.f90
new file mode 100644
index 0000000000000..e047cf838f9ea
--- /dev/null
+++ b/flang/test/Semantics/PowerPC/ppc-vector-poly-checks.f90
@@ -0,0 +1,45 @@
+! RUN: %python %S/../test_errors.py %s %flang_fc1
+! REQUIRES: target=powerpc{{.*}}
+
+! Test that vector types are rejected in polymorphic contexts:
+!   1. ALLOCATE SOURCE=/MOLD= must not have a vector type expression
+!   2. RHS of intrinsic assignment must not be a vector type when LHS is polymorphic
+!      (uses Fortran standard auto-allocation, no prior ALLOCATE)
+!   3. SAME_TYPE_AS / EXTENDS_TYPE_OF must not receive a vector type argument
+!      (enforced via IsExtensibleType returning false for vector types)
+
+subroutine test_allocate_source()
+  vector(integer(4)) :: vi(2)
+  class(*), allocatable :: x(:)
+  !ERROR: SOURCE or MOLD expression must not be a vector type 'vector(integer(4))'
+  allocate(x(2), source=vi)
+end subroutine
+
+subroutine test_allocate_mold()
+  vector(real(4)) :: vr(2)
+  class(*), allocatable :: x(:)
+  !ERROR: SOURCE or MOLD expression must not be a vector type 'vector(real(4))'
+  allocate(x(2), mold=vr)
+end subroutine
+
+subroutine test_poly_assign_vector_rhs()
+  vector(real(4)) :: vr(2)
+  class(*), allocatable :: x(:)
+  ! x is unallocated; auto-allocation from RHS type must be rejected
+  !ERROR: Vector type 'vector(real(4))' may not be used as the right-hand side of a polymorphic intrinsic assignment
+  x = vr
+end subroutine
+
+subroutine test_same_type_as()
+  vector(integer(4)) :: vi(2)
+  logical :: res
+  !ERROR: Actual argument for 'a=' has type 'vector(integer(4))', but was expected to be an extensible or unlimited polymorphic type
+  res = same_type_as(vi, vi)
+end subroutine
+
+subroutine test_extends_type_of()
+  vector(real(4)) :: vr(2)
+  logical :: res
+  !ERROR: Actual argument for 'a=' has type 'vector(real(4))', but was expected to be an extensible or unlimited polymorphic type
+  res = extends_type_of(vr, vr)
+end subroutine