================
@@ -15749,6 +15757,186 @@ StmtResult
SemaOpenMP::ActOnOpenMPUnrollDirective(ArrayRef<OMPClause *> Clauses,
buildPreInits(Context, PreInits));
}
+StmtResult SemaOpenMP::ActOnOpenMPReverseDirective(Stmt *AStmt,
+ SourceLocation StartLoc,
+ SourceLocation EndLoc) {
+ ASTContext &Context = getASTContext();
+ Scope *CurScope = SemaRef.getCurScope();
+
+ // Empty statement should only be possible if there already was an error.
+ if (!AStmt)
+ return StmtError();
+
+ constexpr unsigned NumLoops = 1;
+ Stmt *Body = nullptr;
+ SmallVector<OMPLoopBasedDirective::HelperExprs, NumLoops> LoopHelpers(
+ NumLoops);
+ SmallVector<SmallVector<Stmt *, 0>, NumLoops + 1> OriginalInits;
+ if (!checkTransformableLoopNest(OMPD_reverse, AStmt, NumLoops, LoopHelpers,
+ Body, OriginalInits))
+ return StmtError();
+
+ // Delay applying the transformation to when template is completely
+ // instantiated.
+ if (SemaRef.CurContext->isDependentContext())
+ return OMPReverseDirective::Create(Context, StartLoc, EndLoc, AStmt,
+ nullptr, nullptr);
+
+ assert(LoopHelpers.size() == NumLoops &&
+ "Expecting a single-dimensional loop iteration space");
+ assert(OriginalInits.size() == NumLoops &&
+ "Expecting a single-dimensional loop iteration space");
+ OMPLoopBasedDirective::HelperExprs &LoopHelper = LoopHelpers.front();
+
+ // Find the loop statement.
+ Stmt *LoopStmt = nullptr;
+ collectLoopStmts(AStmt, {LoopStmt});
+
+ // Determine the PreInit declarations.
+ SmallVector<Stmt *> PreInits;
+ addLoopPreInits(Context, LoopHelper, LoopStmt, OriginalInits[0], PreInits);
+
+ auto *IterationVarRef = cast<DeclRefExpr>(LoopHelper.IterationVarRef);
+ QualType IVTy = IterationVarRef->getType();
+ uint64_t IVWidth = Context.getTypeSize(IVTy);
+ auto *OrigVar = cast<DeclRefExpr>(LoopHelper.Counters.front());
+
+ // Iteration variable SourceLocations.
+ SourceLocation OrigVarLoc = OrigVar->getExprLoc();
+ SourceLocation OrigVarLocBegin = OrigVar->getBeginLoc();
+ SourceLocation OrigVarLocEnd = OrigVar->getEndLoc();
+
+ // Locations pointing to the transformation.
+ SourceLocation TransformLoc = StartLoc;
+ SourceLocation TransformLocBegin = StartLoc;
+ SourceLocation TransformLocEnd = EndLoc;
+
+ // Internal variable names.
+ std::string OrigVarName = OrigVar->getNameInfo().getAsString();
+ std::string TripCountName = (Twine(".tripcount.") + OrigVarName).str();
+ std::string ForwardIVName = (Twine(".forward.iv.") + OrigVarName).str();
+ std::string ReversedIVName = (Twine(".reversed.iv.") + OrigVarName).str();
----------------
Meinersbur wrote:
`Twine` stores a non-owning reference to its argument, here `OrigVarName`. If
that string goes out of scope or is changed, that becomes a dangling reference.
`Twine` was designed to be valid within a statement only; at the end of that
statement temporaries may be released. From `Twine.h`:
```
/// A Twine is not intended for use directly and should not be stored, its
/// implementation relies on the ability to store pointers to temporary stack
/// objects which may be deallocated at the end of a statement. Twines should
/// only be used as const references in arguments, when an API wishes
/// to accept possibly-concatenated strings.
```
In this case only two strings are concatenated, so there are no temporary
strings that `Twine` could help avoiding. I may still have used `Twine` here
because either I originally also appended a suffix, or expected `Twine` to
benefit from being able to precompute the target string length. If that's the
case, `std::string::operator+` should be able to do the same. Let me remove
`Twine` here completely.
https://github.com/llvm/llvm-project/pull/92916
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