[flang-commits] [flang] [flang][OpenMP] Implement collapse for imperfectly nested loops (PR #202435)

[Caroline Newcombe via flang-commits]

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@@ -678,6 +679,145 @@ static void genNestedEvaluations(lower::AbstractConverter &converter,
     converter.genEval(e);
 }
 
+/// Emit the body of a collapsed loop nest, including any intervening code
+/// from imperfect nesting at intermediate levels (CLN relaxation, applied
+/// retroactively for all OMP versions).
+///
+/// Because omp.loop_nest places its entire body at the innermost nesting
+/// level, intervening code must be guarded so that it only executes on the
+/// iterations where the corresponding inner induction variables are at their
+/// initial (for intervening code before nested loop) or final (for intervening
+/// code after nested loop) values.
+///
+/// \param [in] converter - PFT to MLIR conversion interface.
+/// \param [in] outerEval - the evaluation containing the outermost loop
+///                         (typically the OpenMP construct evaluation).
+/// \param [in] collapseValue - number of loops being collapsed (>= 1).
+static void genCollapsedLoopNestBody(lower::AbstractConverter &converter,
+                                     lower::pft::Evaluation &outerEval,
+                                     int collapseValue) {
+  assert(collapseValue >= 1);
+  if (collapseValue == 1) {
+    genNestedEvaluations(converter, outerEval, /*collapseValue=*/1);
+    return;
+  }
+
+  fir::FirOpBuilder &firOpBuilder{converter.getFirOpBuilder()};
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cenewcombe wrote:

I was off for a few days and just got this fixed ✔️ 

https://github.com/llvm/llvm-project/pull/202435