[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

5 files changed, 28 insertions, 12 deletions

diff --git a/clang/lib/Basic/TargetInfo.cpp b/clang/lib/Basic/TargetInfo.cpp
index 9ae466b7869..c58ed1e300e 100644
--- a/clang/lib/Basic/TargetInfo.cpp
+++ b/clang/lib/Basic/TargetInfo.cpp
@@ -31,6 +31,7 @@ TargetInfo::TargetInfo(const llvm::Triple &T) : TargetOpts(), Triple(T) {
   // SPARC.  These should be overridden by concrete targets as needed.
   BigEndian = !T.isLittleEndian();
   TLSSupported = true;
+  VLASupported = true;
   NoAsmVariants = false;
   HasFloat128 = false;
   PointerWidth = PointerAlign = 32;
diff --git a/clang/lib/Basic/Targets/NVPTX.cpp b/clang/lib/Basic/Targets/NVPTX.cpp
index 3889f097350..add3b318aeb 100644
--- a/clang/lib/Basic/Targets/NVPTX.cpp
+++ b/clang/lib/Basic/Targets/NVPTX.cpp
@@ -41,6 +41,7 @@ NVPTXTargetInfo::NVPTXTargetInfo(const llvm::Triple &Triple,
          "NVPTX only supports 32- and 64-bit modes.");
 
   TLSSupported = false;
+  VLASupported = false;
   AddrSpaceMap = &NVPTXAddrSpaceMap;
   UseAddrSpaceMapMangling = true;
 
diff --git a/clang/lib/Basic/Targets/SPIR.h b/clang/lib/Basic/Targets/SPIR.h
index e64ad548290..c384d4260ca 100644
--- a/clang/lib/Basic/Targets/SPIR.h
+++ b/clang/lib/Basic/Targets/SPIR.h
@@ -43,6 +43,7 @@ public:
     assert(getTriple().getEnvironment() == llvm::Triple::UnknownEnvironment &&
            "SPIR target must use unknown environment type");
     TLSSupported = false;
+    VLASupported = false;
     LongWidth = LongAlign = 64;
     AddrSpaceMap = &SPIRAddrSpaceMap;
     UseAddrSpaceMapMangling = true;
diff --git a/clang/lib/Sema/SemaOpenMP.cpp b/clang/lib/Sema/SemaOpenMP.cpp
index 0a48133721d..0f349bb961f 100644
--- a/clang/lib/Sema/SemaOpenMP.cpp
+++ b/clang/lib/Sema/SemaOpenMP.cpp
@@ -1303,6 +1303,17 @@ unsigned Sema::getOpenMPNestingLevel() const {
   return DSAStack->getNestingLevel();
 }
 
+bool Sema::isInOpenMPTargetExecutionDirective() const {
+  return (isOpenMPTargetExecutionDirective(DSAStack->getCurrentDirective()) &&
+          !DSAStack->isClauseParsingMode()) ||
+         DSAStack->hasDirective(
+             [](OpenMPDirectiveKind K, const DeclarationNameInfo &,
+                SourceLocation) -> bool {
+               return isOpenMPTargetExecutionDirective(K);
+             },
+             false);
+}
+
 VarDecl *Sema::IsOpenMPCapturedDecl(ValueDecl *D) {
   assert(LangOpts.OpenMP && "OpenMP is not allowed");
   D = getCanonicalDecl(D);
@@ -1315,18 +1326,8 @@ VarDecl *Sema::IsOpenMPCapturedDecl(ValueDecl *D) {
   // inserted here once support for 'declare target' is added.
   //
   auto *VD = dyn_cast<VarDecl>(D);
-  if (VD && !VD->hasLocalStorage()) {
-    if (isOpenMPTargetExecutionDirective(DSAStack->getCurrentDirective()) &&
-        !DSAStack->isClauseParsingMode())
-      return VD;
-    if (DSAStack->hasDirective(
-            [](OpenMPDirectiveKind K, const DeclarationNameInfo &,
-               SourceLocation) -> bool {
-              return isOpenMPTargetExecutionDirective(K);
-            },
-            false))
-      return VD;
-  }
+  if (VD && !VD->hasLocalStorage() && isInOpenMPTargetExecutionDirective())
+    return VD;
 
   if (DSAStack->getCurrentDirective() != OMPD_unknown &&
       (!DSAStack->isClauseParsingMode() ||
@@ -9812,6 +9813,12 @@ static bool ActOnOMPReductionKindClause(
     if ((OASE && !ConstantLengthOASE) ||
         (!OASE && !ASE &&
          D->getType().getNonReferenceType()->isVariablyModifiedType())) {
+      if (!Context.getTargetInfo().isVLASupported() &&
+          S.shouldDiagnoseTargetSupportFromOpenMP()) {
+        S.Diag(ELoc, diag::err_omp_reduction_vla_unsupported) << !!OASE;
+        S.Diag(ELoc, diag::note_vla_unsupported);
+        continue;
+      }
       // For arrays/array sections only:
       // Create pseudo array type for private copy. The size for this array will
       // be generated during codegen.
diff --git a/clang/lib/Sema/SemaType.cpp b/clang/lib/Sema/SemaType.cpp
index ec0d93cf678..b00cf7311b9 100644
--- a/clang/lib/Sema/SemaType.cpp
+++ b/clang/lib/Sema/SemaType.cpp
@@ -2183,6 +2183,12 @@ QualType Sema::BuildArrayType(QualType T, ArrayType::ArraySizeModifier ASM,
   // CUDA device code doesn't support VLAs.
   if (getLangOpts().CUDA && T->isVariableArrayType())
     CUDADiagIfDeviceCode(Loc, diag::err_cuda_vla) << CurrentCUDATarget();
+  // Some targets don't support VLAs.
+  if (T->isVariableArrayType() && !Context.getTargetInfo().isVLASupported() &&
+      shouldDiagnoseTargetSupportFromOpenMP()) {
+    Diag(Loc, diag::err_vla_unsupported);
+    return QualType();
+  }
 
   // If this is not C99, extwarn about VLA's and C99 array size modifiers.
   if (!getLangOpts().C99) {