[mlir][OpenMP] Fix reduction selection when debug data is present.

It was reported that 455.seismic will mis-compare when run with high value of
 LIBOMPTARGET_AMDGPU_TEAMS_PER_CU (e.g. 1024). This started happening after
 debug info was enabled for the target region. After investigation, I have
 observed 2 issues.

1. The `teamsReductionContainedInDistribute` function can choose between doing
reduction on team or distribute construct. The mismatch in the benchmark happens
if the reduction is done on team. This happens irrespective of debug info is
enabled or not. An easy way to test is to return false from this function and
455.seismic will fail every time with LIBOMPTARGET_AMDGPU_TEAMS_PER_CU=1024.

2. The `teamsReductionContainedInDistribute` works by checking that distributeOp
is the only user of reduction variable in teamsOp. This check failed with debug
info as there were some debug uses too.

This PR fixes the 2nd issue. Now with debug info present, the distribute
reduction is done and the problem in 455.seismic goes away. But we still need to
investigate what causes the 1st issue.

Author: abidh

mlir/lib/Target/LLVMIR/Dialect/OpenMP/OpenMPToLLVMIRTranslation.cpp

@@ -1718,10 +1718,18 @@ static bool teamsReductionContainedInDistribute(omp::TeamsOp teamsOp) {
       llvm::cast<mlir::omp::BlockArgOpenMPOpInterface>(teamsOp.getOperation());
   // Check that all uses of the reduction block arg has the same distribute op
   // parent.
+  llvm::SmallVector<mlir::Operation *> debugUses;
   Operation *distOp = nullptr;
   for (auto ra : iface.getReductionBlockArgs())
     for (auto &use : ra.getUses()) {
       auto *useOp = use.getOwner();
+      // Ignore debug uses.
+      if (mlir::isa<LLVM::DbgDeclareOp>(useOp) ||
+          mlir::isa<LLVM::DbgValueOp>(useOp)) {
+        debugUses.push_back(useOp);
+        continue;
+      }
+
       auto currentDistOp = useOp->getParentOfType<omp::DistributeOp>();
       // Use is not inside a distribute op - return false
       if (!currentDistOp)
@@ -1733,6 +1741,12 @@ static bool teamsReductionContainedInDistribute(omp::TeamsOp teamsOp) {
 
       distOp = currentOp;
     }
+
+  // If we are going to use distribute reduction then remove any debug uses of
+  // the reduction parameters in teamsOp. Otherwise they will be left without
+  // any mapped value in moduleTranslation and will eventually error out.
+  for (auto use : debugUses)
+    use->erase();
   return true;
 }