[OPENMP]Honor constantness of captured variables.

[ABataev]

Summary

Fixes bug reported via Stackoverflow:
https://stackoverflow.com/questions/64179168/clang-overload-resolution-failure-with-templates-and-openmp-collapse

Need to honor constantness of private/target variables to make the code
compilable.

clang/lib/Sema/SemaExpr.cpp

if (getLangOpts().OpenMP) {
           // target region, therefore we need to propagate the capture from the
           // enclosing region. Therefore, the capture is not initially nested.
           if (IsTargetCap)
             adjustOpenMPTargetScopeIndex(FunctionScopesIndex, RSI->OpenMPLevel);
 
           if (IsTargetCap || IsOpenMPPrivateDecl == OMPC_private ||
               (IsGlobal && !IsGlobalCap)) {
             Nested = !IsTargetCap;
+            bool HasConst = DeclRefType.isConstQualified();
             DeclRefType = DeclRefType.getUnqualifiedType();
+            // Don't lose diagnostics about assignments to const.
+            if (HasConst)
+              DeclRefType.addConst();
             CaptureType = Context.getLValueReferenceType(DeclRefType);
             break;
           }
         }
       }
     }
     if (CSI->ImpCaptureStyle == CapturingScopeInfo::ImpCap_None && !Explicit) {
       // No capture-default, and this is not an explicit capture

clang/test/OpenMP/distribute_firstprivate_messages.cpp

 const float S2::S2sc = 0;
 const S2 b;
 const S2 ba[5];
 class S3 {
   int a;
   S3 &operator=(const S3 &s3);
 
 public:
-  S3() : a(0) {} // expected-note {{candidate constructor not viable: requires 0 arguments, but 1 was provided}}
-  S3(S3 &s3) : a(s3.a) {} // expected-note {{candidate constructor not viable: 1st argument ('const S3') would lose const qualifier}}
+  S3() : a(0) {} // expected-note 2 {{candidate constructor not viable: requires 0 arguments, but 1 was provided}}
+  S3(S3 &s3) : a(s3.a) {} // expected-note 2 {{candidate constructor not viable: 1st argument ('const S3') would lose const qualifier}}
 };
 const S3 c;
 const S3 ca[5];
 extern const int f;
 class S4 {
   int a;
   S4();
   S4(const S4 &s4);
int main(int argc, char **argv) {
   #pragma omp distribute firstprivate (argc) allocate , allocate(, allocate(omp_default , allocate(omp_default_mem_alloc, allocate(omp_default_mem_alloc:, allocate(omp_default_mem_alloc: argc, allocate(omp_default_mem_alloc: argv), allocate(argv) // expected-error {{expected '(' after 'allocate'}} expected-error 2 {{expected expression}} expected-error 2 {{expected ')'}} expected-error {{use of undeclared identifier 'omp_default'}} expected-note 2 {{to match this '('}}
   for (i = 0; i < argc; ++i) foo();
   #pragma omp target
   #pragma omp teams
   #pragma omp distribute firstprivate (S1) // expected-error {{'S1' does not refer to a value}}
   for (i = 0; i < argc; ++i) foo();
   #pragma omp target
   #pragma omp teams
-  #pragma omp distribute firstprivate (a, b, c, d, f) // expected-error {{firstprivate variable with incomplete type 'S1'}} expected-warning {{Type 'const S2' is not trivially copyable and not guaranteed to be mapped correctly}} expected-warning {{Type 'const S3' is not trivially copyable and not guaranteed to be mapped correctly}} expected-error {{incomplete type 'S1' where a complete type is required}}
+  #pragma omp distribute firstprivate (a, b, c, d, f) // expected-error {{firstprivate variable with incomplete type 'S1'}} expected-warning {{Type 'const S2' is not trivially copyable and not guaranteed to be mapped correctly}} expected-warning {{Type 'const S3' is not trivially copyable and not guaranteed to be mapped correctly}} expected-error {{incomplete type 'S1' where a complete type is required}} expected-error {{no matching constructor for initialization of 'S3'}}
   for (i = 0; i < argc; ++i) foo();
   #pragma omp target
   #pragma omp teams
   #pragma omp distribute firstprivate (argv[1]) // expected-error {{expected variable name}}
   for (i = 0; i < argc; ++i) foo();
   #pragma omp target
   #pragma omp teams
   #pragma omp distribute firstprivate(ba) // expected-warning {{Type 'const S2 [5]' is not trivially copyable and not guaranteed to be mapped correctly}}

clang/test/OpenMP/openmp_capture_const_var_ast_print.cpp

+// RUN: %clang_cc1 -verify -fopenmp -ast-print %s | FileCheck %s
+// RUN: %clang_cc1 -fopenmp -x c++ -std=c++11 -emit-pch -o %t %s
+// RUN: %clang_cc1 -fopenmp -std=c++11 -include-pch %t -fsyntax-only -verify %s -ast-print | FileCheck %s
+
+// RUN: %clang_cc1 -verify -fopenmp-simd -ast-print %s | FileCheck %s
+// RUN: %clang_cc1 -fopenmp-simd -x c++ -std=c++11 -emit-pch -o %t %s
+// RUN: %clang_cc1 -fopenmp-simd -std=c++11 -include-pch %t -fsyntax-only -verify %s -ast-print | FileCheck %s
+// expected-no-diagnostics
+
+#ifndef HEADER
+#define HEADER
+
+struct vector {
+  vector() = default;
+  int at(int) { return 0; }
+  int at(int) const { return 1; }
+};
+
+// CHECK: template <typename T> void test(const vector begin_vec) {
+// CHECK:    #pragma omp parallel for collapse(2)
+// CHECK:        for (int n = begin_vec.at(0); n < 0; n++) {
+// CHECK:            for (int h = begin_vec.at(1); h < 1; h++) {
+// CHECK:                ;
+// CHECK:            }
+// CHECK:        }
+// CHECK: }
+// CHECK: template<> void test<int>(const vector begin_vec) {
+// CHECK:    #pragma omp parallel for collapse(2)
+// CHECK:        for (int n = begin_vec.at(0); n < 0; n++) {
+// CHECK:            for (int h = begin_vec.at(1); h < 1; h++) {
+// CHECK:                ;
+// CHECK:            }
+// CHECK:        }
+// CHECK: }
+template <typename T>
+void test(const vector begin_vec) {
+#pragma omp parallel for collapse(2)
+  for (int n = begin_vec.at(0); n < 0; n++) {
+    for (int h = begin_vec.at(1); h < 1; h++) {
+      ;
+    }
+  }
+}
+
+int main() {
+  vector v;
+  test<int>(v);
+}
+#endif

clang/test/OpenMP/teams_distribute_firstprivate_messages.cpp

 const float S2::S2sc = 0;
 const S2 b;
 const S2 ba[5];
 class S3 {
   int a;
   S3 &operator=(const S3 &s3);
   
 public:
-  S3() : a(0) {} // expected-note {{candidate constructor not viable: requires 0 arguments, but 1 was provided}}
-  S3(S3 &s3) : a(s3.a) {} // expected-note {{candidate constructor not viable: 1st argument ('const S3') would lose const qualifier}}
+  S3() : a(0) {} // expected-note 2 {{candidate constructor not viable: requires 0 arguments, but 1 was provided}}
+  S3(S3 &s3) : a(s3.a) {} // expected-note 2 {{candidate constructor not viable: 1st argument ('const S3') would lose const qualifier}}
 };
 const S3 c;
 const S3 ca[5];
 extern const int f;
 class S4 {
   int a;
   S4();
   S4(const S4 &s4);

 #pragma omp teams distribute firstprivate (argc) allocate , allocate(, allocate(omp_default , allocate(omp_default_mem_alloc, allocate(omp_default_mem_alloc:, allocate(omp_default_mem_alloc: argc, allocate(omp_default_mem_alloc: argv), allocate(argv) // expected-error {{expected '(' after 'allocate'}} expected-error 2 {{expected expression}} expected-error 2 {{expected ')'}} expected-error {{use of undeclared identifier 'omp_default'}} expected-note 2 {{to match this '('}}
   for (i = 0; i < argc; ++i) foo();
 
 #pragma omp target
 #pragma omp teams distribute firstprivate (S1) // expected-error {{'S1' does not refer to a value}}
   for (i = 0; i < argc; ++i) foo();
 
 #pragma omp target
-#pragma omp teams distribute firstprivate (a, b, c, d, f) // expected-error {{firstprivate variable with incomplete type 'S1'}} expected-error {{incomplete type 'S1' where a complete type is required}}
+#pragma omp teams distribute firstprivate (a, b, c, d, f) // expected-error {{firstprivate variable with incomplete type 'S1'}} expected-error {{incomplete type 'S1' where a complete type is required}} expected-error {{no matching constructor for initialization of 'S3'}}
   for (i = 0; i < argc; ++i) foo();
 
 #pragma omp target
 #pragma omp teams distribute firstprivate (argv[1]) // expected-error {{expected variable name}}
   for (i = 0; i < argc; ++i) foo();
 
 #pragma omp target
 #pragma omp teams distribute firstprivate(ba, z)

clang/test/OpenMP/teams_distribute_parallel_for_firstprivate_messages.cpp

 const float S2::S2sc = 0;
 const S2 b;
 const S2 ba[5];
 class S3 {
   int a;
   S3 &operator=(const S3 &s3);
   
 public:
-  S3() : a(0) {} // expected-note {{candidate constructor not viable: requires 0 arguments, but 1 was provided}}
-  S3(S3 &s3) : a(s3.a) {} // expected-note {{candidate constructor not viable: 1st argument ('const S3') would lose const qualifier}}
+  S3() : a(0) {} // expected-note 2 {{candidate constructor not viable: requires 0 arguments, but 1 was provided}}
+  S3(S3 &s3) : a(s3.a) {} // expected-note 2 {{candidate constructor not viable: 1st argument ('const S3') would lose const qualifier}}
 };
 const S3 c;
 const S3 ca[5];
 extern const int f;
 class S4 {
   int a;
   S4();
   S4(const S4 &s4);

 #pragma omp teams distribute parallel for firstprivate (argc) allocate , allocate(, allocate(omp_default , allocate(omp_default_mem_alloc, allocate(omp_default_mem_alloc:, allocate(omp_default_mem_alloc: argc, allocate(omp_default_mem_alloc: argv), allocate(argv) // expected-error {{expected '(' after 'allocate'}} expected-error 2 {{expected expression}} expected-error 2 {{expected ')'}} expected-error {{use of undeclared identifier 'omp_default'}} expected-note 2 {{to match this '('}}
   for (i = 0; i < argc; ++i) foo();
 
 #pragma omp target
 #pragma omp teams distribute parallel for firstprivate (S1) // expected-error {{'S1' does not refer to a value}}
   for (i = 0; i < argc; ++i) foo();
 
 #pragma omp target
-#pragma omp teams distribute parallel for firstprivate (a, b, c, d, f) // expected-error {{firstprivate variable with incomplete type 'S1'}} expected-error {{incomplete type 'S1' where a complete type is required}}
+#pragma omp teams distribute parallel for firstprivate (a, b, c, d, f) // expected-error {{firstprivate variable with incomplete type 'S1'}} expected-error {{incomplete type 'S1' where a complete type is required}} expected-error {{no matching constructor for initialization of 'S3'}}
   for (i = 0; i < argc; ++i) foo();
 
 #pragma omp target
 #pragma omp teams distribute parallel for firstprivate (argv[1]) // expected-error {{expected variable name}}
   for (i = 0; i < argc; ++i) foo();
 
 #pragma omp target
 #pragma omp teams distribute parallel for firstprivate(ba)

clang/test/OpenMP/teams_distribute_parallel_for_simd_firstprivate_messages.cpp

 const float S2::S2sc = 0;
 const S2 b;
 const S2 ba[5];
 class S3 {
   int a;
   S3 &operator=(const S3 &s3);
   
 public:
-  S3() : a(0) {} // expected-note {{candidate constructor not viable: requires 0 arguments, but 1 was provided}}
-  S3(S3 &s3) : a(s3.a) {} // expected-note {{candidate constructor not viable: 1st argument ('const S3') would lose const qualifier}}
+  S3() : a(0) {} // expected-note 2 {{candidate constructor not viable: requires 0 arguments, but 1 was provided}}
+  S3(S3 &s3) : a(s3.a) {} // expected-note 2 {{candidate constructor not viable: 1st argument ('const S3') would lose const qualifier}}
 };
 const S3 c;
 const S3 ca[5];
 extern const int f;
 class S4 {
   int a;
   S4();
   S4(const S4 &s4);

 #pragma omp teams distribute parallel for simd firstprivate (argc) allocate , allocate(, allocate(omp_default , allocate(omp_default_mem_alloc, allocate(omp_default_mem_alloc:, allocate(omp_default_mem_alloc: argc, allocate(omp_default_mem_alloc: argv), allocate(argv) // expected-error {{expected '(' after 'allocate'}} expected-error 2 {{expected expression}} expected-error 2 {{expected ')'}} expected-error {{use of undeclared identifier 'omp_default'}} expected-note 2 {{to match this '('}}
   for (i = 0; i < argc; ++i) foo();
 
 #pragma omp target
 #pragma omp teams distribute parallel for simd firstprivate (S1) // expected-error {{'S1' does not refer to a value}}
   for (i = 0; i < argc; ++i) foo();
 
 #pragma omp target
-#pragma omp teams distribute parallel for simd firstprivate (a, b, c, d, f) // expected-error {{firstprivate variable with incomplete type 'S1'}} expected-error {{incomplete type 'S1' where a complete type is required}}
+#pragma omp teams distribute parallel for simd firstprivate (a, b, c, d, f) // expected-error {{firstprivate variable with incomplete type 'S1'}} expected-error {{incomplete type 'S1' where a complete type is required}} expected-error {{no matching constructor for initialization of 'S3'}}
   for (i = 0; i < argc; ++i) foo();
 
 #pragma omp target
 #pragma omp teams distribute parallel for simd firstprivate (argv[1]) // expected-error {{expected variable name}}
   for (i = 0; i < argc; ++i) foo();
 
 #pragma omp target
 #pragma omp teams distribute parallel for simd firstprivate(ba, z)

clang/test/OpenMP/teams_distribute_simd_firstprivate_messages.cpp

 const float S2::S2sc = 0;
 const S2 b;
 const S2 ba[5];
 class S3 {
   int a;
   S3 &operator=(const S3 &s3);
   
 public:
-  S3() : a(0) {} // expected-note {{candidate constructor not viable: requires 0 arguments, but 1 was provided}}
-  S3(S3 &s3) : a(s3.a) {} // expected-note {{candidate constructor not viable: 1st argument ('const S3') would lose const qualifier}}
+  S3() : a(0) {} // expected-note 2 {{candidate constructor not viable: requires 0 arguments, but 1 was provided}}
+  S3(S3 &s3) : a(s3.a) {} // expected-note 2 {{candidate constructor not viable: 1st argument ('const S3') would lose const qualifier}}
 };
 const S3 c;
 const S3 ca[5];
 extern const int f;
 class S4 {
   int a;
   S4();
   S4(const S4 &s4);

 #pragma omp teams distribute simd firstprivate (argc) allocate , allocate(, allocate(omp_default , allocate(omp_default_mem_alloc, allocate(omp_default_mem_alloc:, allocate(omp_default_mem_alloc: argc, allocate(omp_default_mem_alloc: argv), allocate(argv) // expected-error {{expected '(' after 'allocate'}} expected-error 2 {{expected expression}} expected-error 2 {{expected ')'}} expected-error {{use of undeclared identifier 'omp_default'}} expected-note 2 {{to match this '('}}
   for (i = 0; i < argc; ++i) foo();
 
 #pragma omp target
 #pragma omp teams distribute simd firstprivate (S1) // expected-error {{'S1' does not refer to a value}}
   for (i = 0; i < argc; ++i) foo();
 
 #pragma omp target
-#pragma omp teams distribute simd firstprivate (k, a, b, c, d, f) // expected-error {{firstprivate variable with incomplete type 'S1'}} expected-error {{incomplete type 'S1' where a complete type is required}}
+#pragma omp teams distribute simd firstprivate (k, a, b, c, d, f) // expected-error {{firstprivate variable with incomplete type 'S1'}} expected-error {{incomplete type 'S1' where a complete type is required}} expected-error {{no matching constructor for initialization of 'S3'}}
   for (i = 0; i < argc; ++i) foo();
 
 #pragma omp target
 #pragma omp teams distribute simd firstprivate (argv[1]) // expected-error {{expected variable name}}
   for (i = 0; i < argc; ++i) foo();
 
 #pragma omp target
 #pragma omp teams distribute simd firstprivate(ba)