[OpenMP] Show error if VLAs are not supported

Some target devices (e.g. Nvidia GPUs) don't support dynamic stack
allocation and hence no VLAs. Print errors with description instead
of failing in the backend or generating code that doesn't work.

This patch handles explicit uses of VLAs (local variable in target
or declare target region) or implicitly generated (private) VLAs
for reductions on VLAs or on array sections with non-constant size.

Differential Revision: https://reviews.llvm.org/D39505

llvm-svn: 318601

1 files changed, 201 insertions, 0 deletions

diff --git a/clang/test/OpenMP/target_vla_messages.cpp b/clang/test/OpenMP/target_vla_messages.cpp
new file mode 100644
index 00000000000..c970d0def66
--- /dev/null
+++ b/clang/test/OpenMP/target_vla_messages.cpp
@@ -0,0 +1,201 @@
+// PowerPC supports VLAs.
+// RUN: %clang_cc1 -verify -fopenmp -x c++ -triple powerpc64le-unknown-unknown -fopenmp-targets=powerpc64le-unknown-unknown -emit-llvm-bc %s -o %t-ppc-host-ppc.bc
+// RUN: %clang_cc1 -verify -fopenmp -x c++ -triple powerpc64le-unknown-unknown -fopenmp-targets=powerpc64le-unknown-unknown -emit-llvm %s -fopenmp-is-device -fopenmp-host-ir-file-path %t-ppc-host-ppc.bc -o %t-ppc-device.ll
+
+// Nvidia GPUs don't support VLAs.
+// RUN: %clang_cc1 -verify -fopenmp -x c++ -triple powerpc64le-unknown-unknown -fopenmp-targets=nvptx64-nvidia-cuda -emit-llvm-bc %s -o %t-ppc-host-nvptx.bc
+// RUN: %clang_cc1 -verify -DNO_VLA -fopenmp -x c++ -triple nvptx64-unknown-unknown -fopenmp-targets=nvptx64-nvidia-cuda -emit-llvm %s -fopenmp-is-device -fopenmp-host-ir-file-path %t-ppc-host-nvptx.bc -o %t-nvptx-device.ll
+
+#ifndef NO_VLA
+// expected-no-diagnostics
+#endif
+
+#pragma omp declare target
+void declare(int arg) {
+  int a[2];
+#ifdef NO_VLA
+  // expected-error@+2 {{variable length arrays are not supported for the current target}}
+#endif
+  int vla[arg];
+}
+
+void declare_parallel_reduction(int arg) {
+  int a[2];
+
+#pragma omp parallel reduction(+: a)
+  { }
+
+#pragma omp parallel reduction(+: a[0:2])
+  { }
+
+#ifdef NO_VLA
+  // expected-error@+3 {{cannot generate code for reduction on array section, which requires a variable length array}}
+  // expected-note@+2 {{variable length arrays are not supported for the current target}}
+#endif
+#pragma omp parallel reduction(+: a[0:arg])
+  { }
+}
+#pragma omp end declare target
+
+template <typename T>
+void target_template(int arg) {  
+#pragma omp target
+  {
+#ifdef NO_VLA
+    // expected-error@+2 {{variable length arrays are not supported for the current target}}
+#endif
+    T vla[arg];
+  }
+}
+
+void target(int arg) {
+#pragma omp target
+  {
+#ifdef NO_VLA
+    // expected-error@+2 {{variable length arrays are not supported for the current target}}
+#endif
+    int vla[arg];
+  }
+
+#pragma omp target
+  {
+#pragma omp parallel
+    {
+#ifdef NO_VLA
+    // expected-error@+2 {{variable length arrays are not supported for the current target}}
+#endif
+      int vla[arg];
+    }
+  }
+
+  target_template<long>(arg);
+}
+
+void teams_reduction(int arg) {
+  int a[2];
+  int vla[arg];
+
+#pragma omp target map(a)
+#pragma omp teams reduction(+: a)
+  { }
+
+#ifdef NO_VLA
+  // expected-error@+4 {{cannot generate code for reduction on variable length array}}
+  // expected-note@+3 {{variable length arrays are not supported for the current target}}
+#endif
+#pragma omp target map(vla)
+#pragma omp teams reduction(+: vla)
+  { }
+  
+#pragma omp target map(a[0:2])
+#pragma omp teams reduction(+: a[0:2])
+  { }
+
+#pragma omp target map(vla[0:2])
+#pragma omp teams reduction(+: vla[0:2])
+  { }
+
+#ifdef NO_VLA
+  // expected-error@+4 {{cannot generate code for reduction on array section, which requires a variable length array}}
+  // expected-note@+3 {{variable length arrays are not supported for the current target}}
+#endif
+#pragma omp target map(a[0:arg])
+#pragma omp teams reduction(+: a[0:arg])
+  { }
+
+#ifdef NO_VLA
+  // expected-error@+4 {{cannot generate code for reduction on array section, which requires a variable length array}}
+  // expected-note@+3 {{variable length arrays are not supported for the current target}}
+#endif
+#pragma omp target map(vla[0:arg])
+#pragma omp teams reduction(+: vla[0:arg])
+  { }
+}
+
+void parallel_reduction(int arg) {
+  int a[2];
+  int vla[arg];
+
+#pragma omp target map(a)
+#pragma omp parallel reduction(+: a)
+  { }
+
+#ifdef NO_VLA
+  // expected-error@+4 {{cannot generate code for reduction on variable length array}}
+  // expected-note@+3 {{variable length arrays are not supported for the current target}}
+#endif
+#pragma omp target map(vla)
+#pragma omp parallel reduction(+: vla)
+  { }
+
+#pragma omp target map(a[0:2])
+#pragma omp parallel reduction(+: a[0:2])
+  { }
+
+#pragma omp target map(vla[0:2])
+#pragma omp parallel reduction(+: vla[0:2])
+  { }
+
+#ifdef NO_VLA
+  // expected-error@+4 {{cannot generate code for reduction on array section, which requires a variable length array}}
+  // expected-note@+3 {{variable length arrays are not supported for the current target}}
+#endif
+#pragma omp target map(a[0:arg])
+#pragma omp parallel reduction(+: a[0:arg])
+  { }
+
+#ifdef NO_VLA
+  // expected-error@+4 {{cannot generate code for reduction on array section, which requires a variable length array}}
+  // expected-note@+3 {{variable length arrays are not supported for the current target}}
+#endif
+#pragma omp target map(vla[0:arg])
+#pragma omp parallel reduction(+: vla[0:arg])
+  { }
+}
+
+void for_reduction(int arg) {
+  int a[2];
+  int vla[arg];
+
+#pragma omp target map(a)
+#pragma omp parallel
+#pragma omp for reduction(+: a)
+  for (int i = 0; i < arg; i++) ;
+
+#ifdef NO_VLA
+  // expected-error@+5 {{cannot generate code for reduction on variable length array}}
+  // expected-note@+4 {{variable length arrays are not supported for the current target}}
+#endif
+#pragma omp target map(vla)
+#pragma omp parallel
+#pragma omp for reduction(+: vla)
+  for (int i = 0; i < arg; i++) ;
+
+#pragma omp target map(a[0:2])
+#pragma omp parallel
+#pragma omp for reduction(+: a[0:2])
+  for (int i = 0; i < arg; i++) ;
+
+#pragma omp target map(vla[0:2])
+#pragma omp parallel
+#pragma omp for reduction(+: vla[0:2])
+  for (int i = 0; i < arg; i++) ;
+
+#ifdef NO_VLA
+  // expected-error@+5 {{cannot generate code for reduction on array section, which requires a variable length array}}
+  // expected-note@+4 {{variable length arrays are not supported for the current target}}
+#endif
+#pragma omp target map(a[0:arg])
+#pragma omp parallel
+#pragma omp for reduction(+: a[0:arg])
+  for (int i = 0; i < arg; i++) ;
+
+#ifdef NO_VLA
+  // expected-error@+5 {{cannot generate code for reduction on array section, which requires a variable length array}}
+  // expected-note@+4 {{variable length arrays are not supported for the current target}}
+#endif
+#pragma omp target map(vla[0:arg])
+#pragma omp parallel
+#pragma omp for reduction(+: vla[0:arg])
+  for (int i = 0; i < arg; i++) ;
+}