[flang] [llvm] [mlir] [flang][OpenMP] Enable tiling (PR #143715)

[Krzysztof Parzyszek via llvm-commits]

================
@@ -131,20 +133,48 @@ class CanonicalizationOfOmp {
       // Ignore compiler directives.
       if (GetConstructIf<parser::CompilerDirective>(*nextIt))
         continue;
+      // Keep track of the loops to handle the end loop directives
+      std::stack<parser::OpenMPLoopConstruct *> loops;
+      loops.push(&x);
+      if (auto *innerConstruct{
+              GetConstructIf<parser::OpenMPConstruct>(*nextIt)}) {
+        if (auto *innerOmpLoop{
+                std::get_if<parser::OpenMPLoopConstruct>(&innerConstruct->u)}) {
+          auto &innerBeginDir{
+              std::get<parser::OmpBeginLoopDirective>(innerOmpLoop->t)};
+          auto &innerDir{std::get<parser::OmpLoopDirective>(innerBeginDir.t)};
+          if (innerDir.v == llvm::omp::Directive::OMPD_tile) {
+            std::get<std::optional<
+                common::Indirection<parser::OpenMPLoopConstruct>>>(
+                loops.top()->t) = std::move(*innerOmpLoop);
+            // Retrieveing the address so that DoConstruct or inner loop can be
+            // set later.
+            loops.push(&(std::get<std::optional<
+                    common::Indirection<parser::OpenMPLoopConstruct>>>(
+                loops.top()->t)
+                    .value()
+                    .value()));
+            nextIt = block.erase(nextIt);
+          }
+        }
+      }
 
       if (auto *doCons{GetConstructIf<parser::DoConstruct>(*nextIt)}) {
         if (doCons->GetLoopControl()) {
-          // move DoConstruct
-          std::get<std::optional<parser::DoConstruct>>(x.t) =
+          std::get<std::optional<parser::DoConstruct>>(loops.top()->t) =
               std::move(*doCons);
           nextIt = block.erase(nextIt);
           // try to match OmpEndLoopDirective
-          if (nextIt != block.end()) {
+          while (nextIt != block.end() && !loops.empty()) {
             if (auto *endDir{
                     GetConstructIf<parser::OmpEndLoopDirective>(*nextIt)}) {
-              std::get<std::optional<parser::OmpEndLoopDirective>>(x.t) =
-                  std::move(*endDir);
-              block.erase(nextIt);
+              std::get<std::optional<parser::OmpEndLoopDirective>>(
+                  loops.top()->t) = std::move(*endDir);
----------------
kparzysz wrote:

This should check if the actual directive matches the "begin loop" directive, e.g
```
!$omp do
!$omp tile ...
do ...
enddo
!$omp end do    ! should be paired with "do", not "tile"
```

https://github.com/llvm/llvm-project/pull/143715