[OpenMP] Avoid VLAs for some reductions on array sections

In some cases the compiler can deduce the length of an array section
as constants. With this information, VLAs can be avoided in place of
a constant sized array or even a scalar value if the length is 1.
Example:
int a[4], b[2];
pragma omp parallel reduction(+: a[1:2], b[1:1])
{ }

For chained array sections, this optimization is restricted to cases
where all array sections except the last have a constant length 1.
This trivially guarantees that there are no holes in the memory region
that needs to be privatized.
Example:
int c[3][4];
pragma omp parallel reduction(+: c[1:1][1:2])
{ }

Differential Revision: https://reviews.llvm.org/D39136

llvm-svn: 316229

1 files changed, 4 insertions, 6 deletions

diff --git a/clang/lib/CodeGen/CGOpenMPRuntime.cpp b/clang/lib/CodeGen/CGOpenMPRuntime.cpp
index f98ff85565f..3396c63cd62 100644
--- a/clang/lib/CodeGen/CGOpenMPRuntime.cpp
+++ b/clang/lib/CodeGen/CGOpenMPRuntime.cpp
@@ -925,7 +925,7 @@ void ReductionCodeGen::emitAggregateType(CodeGenFunction &CGF, unsigned N) {
       cast<VarDecl>(cast<DeclRefExpr>(ClausesData[N].Private)->getDecl());
   QualType PrivateType = PrivateVD->getType();
   bool AsArraySection = isa<OMPArraySectionExpr>(ClausesData[N].Ref);
-  if (!AsArraySection && !PrivateType->isVariablyModifiedType()) {
+  if (!PrivateType->isVariablyModifiedType()) {
     Sizes.emplace_back(
         CGF.getTypeSize(
             SharedAddresses[N].first.getType().getNonReferenceType()),
@@ -963,10 +963,9 @@ void ReductionCodeGen::emitAggregateType(CodeGenFunction &CGF, unsigned N,
   auto *PrivateVD =
       cast<VarDecl>(cast<DeclRefExpr>(ClausesData[N].Private)->getDecl());
   QualType PrivateType = PrivateVD->getType();
-  bool AsArraySection = isa<OMPArraySectionExpr>(ClausesData[N].Ref);
-  if (!AsArraySection && !PrivateType->isVariablyModifiedType()) {
+  if (!PrivateType->isVariablyModifiedType()) {
     assert(!Size && !Sizes[N].second &&
-           "Size should be nullptr for non-variably modified redution "
+           "Size should be nullptr for non-variably modified reduction "
            "items.");
     return;
   }
@@ -994,8 +993,7 @@ void ReductionCodeGen::emitInitialization(
                                        CGF.ConvertTypeForMem(SharedType)),
       SharedType, SharedAddresses[N].first.getBaseInfo(),
       CGF.CGM.getTBAAAccessInfo(SharedType));
-  if (isa<OMPArraySectionExpr>(ClausesData[N].Ref) ||
-      CGF.getContext().getAsArrayType(PrivateVD->getType())) {
+  if (CGF.getContext().getAsArrayType(PrivateVD->getType())) {
     emitAggregateInitialization(CGF, N, PrivateAddr, SharedLVal, DRD);
   } else if (DRD && (DRD->getInitializer() || !PrivateVD->hasInit())) {
     emitInitWithReductionInitializer(CGF, DRD, ClausesData[N].ReductionOp,