[Flang][OpenMP] Disable lowering of omp.simd reductions in composites (#112686)

Currently, the `omp.simd` operation is ignored during MLIR to LLVM IR
translation when it takes part in a composite construct. One consequence
of this limitation is that any entry block arguments defined by that
operation will trigger a compiler crash if they are used anywhere, as
they are not bound to an LLVM IR value.

A previous PR introducing support for the `reduction` clause resulted in
the creation and use of entry block arguments attached to the `omp.simd`
operation, causing compiler crashes on 'do simd reduction(...)'
constructs.

This patch disables Flang lowering of simd reductions in 'do simd'
constructs to avoid triggering these errors while translation to LLVM IR
is still incomplete.

Author: skatrak

flang/lib/Lower/OpenMP/OpenMP.cpp

@@ -2209,6 +2209,12 @@ static void genCompositeDistributeParallelDoSimd(
   genSimdClauses(converter, semaCtx, simdItem->clauses, loc, simdClauseOps,
                  simdReductionSyms);
 
+  // TODO: Remove this after omp.simd reductions on composite constructs are
+  // supported.
+  simdClauseOps.reductionVars.clear();
+  simdClauseOps.reductionByref.clear();
+  simdClauseOps.reductionSyms.clear();
+
   mlir::omp::LoopNestOperands loopNestClauseOps;
   llvm::SmallVector<const semantics::Symbol *> iv;
   genLoopNestClauses(converter, semaCtx, eval, simdItem->clauses, loc,
@@ -2230,9 +2236,7 @@ static void genCompositeDistributeParallelDoSimd(
   wsloopOp.setComposite(/*val=*/true);
 
   EntryBlockArgs simdArgs;
-  // TODO: Add private syms and vars.
-  simdArgs.reduction.syms = simdReductionSyms;
-  simdArgs.reduction.vars = simdClauseOps.reductionVars;
+  // TODO: Add private and reduction syms and vars.
   auto simdOp =
       genWrapperOp<mlir::omp::SimdOp>(converter, loc, simdClauseOps, simdArgs);
   simdOp.setComposite(/*val=*/true);
@@ -2325,6 +2329,12 @@ static void genCompositeDoSimd(lower::AbstractConverter &converter,
   genSimdClauses(converter, semaCtx, simdItem->clauses, loc, simdClauseOps,
                  simdReductionSyms);
 
+  // TODO: Remove this after omp.simd reductions on composite constructs are
+  // supported.
+  simdClauseOps.reductionVars.clear();
+  simdClauseOps.reductionByref.clear();
+  simdClauseOps.reductionSyms.clear();
+
   // TODO: Support delayed privatization.
   DataSharingProcessor dsp(converter, semaCtx, simdItem->clauses, eval,
                            /*shouldCollectPreDeterminedSymbols=*/true,
@@ -2348,9 +2358,7 @@ static void genCompositeDoSimd(lower::AbstractConverter &converter,
   wsloopOp.setComposite(/*val=*/true);
 
   EntryBlockArgs simdArgs;
-  // TODO: Add private syms and vars.
-  simdArgs.reduction.syms = simdReductionSyms;
-  simdArgs.reduction.vars = simdClauseOps.reductionVars;
+  // TODO: Add private and reduction syms and vars.
   auto simdOp =
       genWrapperOp<mlir::omp::SimdOp>(converter, loc, simdClauseOps, simdArgs);
   simdOp.setComposite(/*val=*/true);