================
@@ -16528,6 +16535,305 @@ StmtResult
SemaOpenMP::ActOnOpenMPInterchangeDirective(
buildPreInits(Context, PreInits));
}
+StmtResult
+SemaOpenMP::ActOnOpenMPFlattenDirective(ArrayRef<OMPClause *> Clauses,
+ Stmt *AStmt, SourceLocation StartLoc,
+ SourceLocation EndLoc) {
+ ASTContext &Context = getASTContext();
+ DeclContext *CurContext = SemaRef.CurContext;
+ Scope *CurScope = SemaRef.getCurScope();
+
+ // Empty statement should only be possible if there already was an error.
+ if (!AStmt)
+ return StmtError();
+
+ // flatten without 'depth' clause combines two loops; 'depth(k)' selects k.
+ unsigned NumLoops = 2;
+ bool DepthIsDependent = false;
+ const auto *DepthClause =
+ OMPExecutableDirective::getSingleClause<OMPDepthClause>(Clauses);
+ if (DepthClause) {
+ Expr *DepthExpr = DepthClause->getDepth();
+ if (DepthExpr && DepthExpr->isInstantiationDependent()) {
+ DepthIsDependent = true;
+ } else if (DepthExpr) {
+ Expr::EvalResult EvalResult;
+ if (DepthExpr->EvaluateAsInt(EvalResult, Context))
+ NumLoops = EvalResult.Val.getInt().getLimitedValue(
+ std::numeric_limits<unsigned>::max());
+ }
+ }
+
+ // Count perfectly nested loops with doForAllLoops. When 'depth' is present,
+ // walk NumLoops iterations to diagnose an insufficient nest. When it is
+ // omitted, walk one extra loop (3 total) so we can warn that default
+ // flatten only combines 2 of a deeper nest.
+ if (!DepthIsDependent) {
+ unsigned WalkLimit = DepthClause ? NumLoops : 3;
+ unsigned Found = 0;
+ bool Enough = OMPLoopBasedDirective::doForAllLoops(
+ AStmt->IgnoreContainers(), /*TryImperfectlyNestedLoops=*/false,
----------------
Meinersbur wrote:
[not a change request] It might be useful to users to get a warning even when
the nested loop is not eligable.
```c
#pragma omp flatten
for (int i = 0; i < 128; ++i)
for (int j = 0; j < 128; ++j)
for (int k = i; k < j; ++k)
```
Even with support for non-rectangular loops, the `k` loop would does not count
as a canonical loop nest (the specification's canonical loop form only allows
one *var-outer* induction variable to appear in lb/ub), hence would not get a
warning.
I don't know what a heuristic catching would be, it might be to warn if any
loop appears in the inner loop body. It still follows the diagnostic policy of
warnings to be actionable: Add `depth(2)` to make clear you want to flatten
only 2 loops.
https://github.com/llvm/llvm-project/pull/206977
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