[flang-commits] [flang] [Flang][OpenMP] Per-sym checks to introduce barriers (PR #127074)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-flang-fir-hlfir

Author: Sergio Afonso (skatrak)

<details>
<summary>Changes</summary>

Whenever there is a `lastprivate` variable and another unrelated variable sets the `mightHaveReadHostSym` flag during Flang lowering privatization, this will result in the insertion of a barrier.

This patch modifies this behavior such that this barrier will not be inserted unless the same symbol both sets the flag and has `lastprivate`.

---
Full diff: https://github.com/llvm/llvm-project/pull/127074.diff


2 Files Affected:

- (modified) flang/lib/Lower/OpenMP/DataSharingProcessor.cpp (+3-3) 
- (modified) flang/lib/Lower/OpenMP/DataSharingProcessor.h (+1-1) 


``````````diff
diff --git a/flang/lib/Lower/OpenMP/DataSharingProcessor.cpp b/flang/lib/Lower/OpenMP/DataSharingProcessor.cpp
index 55f543ca38178..d13f101f516e7 100644
--- a/flang/lib/Lower/OpenMP/DataSharingProcessor.cpp
+++ b/flang/lib/Lower/OpenMP/DataSharingProcessor.cpp
@@ -166,7 +166,7 @@ void DataSharingProcessor::cloneSymbol(const semantics::Symbol *sym) {
 
   if (needInitClone()) {
     Fortran::lower::initializeCloneAtRuntime(converter, *sym, symTable);
-    mightHaveReadHostSym = true;
+    mightHaveReadHostSym.insert(sym);
   }
 }
 
@@ -222,7 +222,7 @@ bool DataSharingProcessor::needBarrier() {
   for (const semantics::Symbol *sym : allPrivatizedSymbols) {
     if (sym->test(semantics::Symbol::Flag::OmpLastPrivate) &&
         (sym->test(semantics::Symbol::Flag::OmpFirstPrivate) ||
-         mightHaveReadHostSym))
+         mightHaveReadHostSym.contains(sym)))
       return true;
   }
   return false;
@@ -594,7 +594,7 @@ void DataSharingProcessor::doPrivatize(const semantics::Symbol *sym,
       // TODO: currently there are false positives from dead uses of the mold
       // arg
       if (!result.getInitMoldArg().getUses().empty())
-        mightHaveReadHostSym = true;
+        mightHaveReadHostSym.insert(sym);
     }
 
     // Populate the `copy` region if this is a `firstprivate`.
diff --git a/flang/lib/Lower/OpenMP/DataSharingProcessor.h b/flang/lib/Lower/OpenMP/DataSharingProcessor.h
index 8e15c6d260389..54a42fd199831 100644
--- a/flang/lib/Lower/OpenMP/DataSharingProcessor.h
+++ b/flang/lib/Lower/OpenMP/DataSharingProcessor.h
@@ -86,7 +86,7 @@ class DataSharingProcessor {
   lower::pft::Evaluation &eval;
   bool shouldCollectPreDeterminedSymbols;
   bool useDelayedPrivatization;
-  bool mightHaveReadHostSym = false;
+  llvm::SmallSet<const semantics::Symbol *, 16> mightHaveReadHostSym;
   lower::SymMap &symTable;
   OMPConstructSymbolVisitor visitor;
 

``````````

</details>


https://github.com/llvm/llvm-project/pull/127074