[llvm] [LoopInterchange] Add metadata to control loop-interchange (PR #127474)

[Ryotaro Kasuga via llvm-commits]

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@@ -572,6 +578,70 @@ struct LoopInterchange {
 
 } // end anonymous namespace
 
+bool LoopInterchangeList::hasSupportedLoopDepth(
+    OptimizationRemarkEmitter &ORE) {
+  unsigned LoopNestDepth = ListEnd - ListBegin;
+  if (LoopNestDepth < MinLoopNestDepth || LoopNestDepth > MaxLoopNestDepth) {
+    LLVM_DEBUG(dbgs() << "Unsupported depth of loop nest " << LoopNestDepth
+                      << ", the supported range is [" << MinLoopNestDepth
+                      << ", " << MaxLoopNestDepth << "].\n");
+    Loop *OuterLoop = LoopList[ListBegin];
+    ORE.emit([&]() {
+      return OptimizationRemarkMissed(DEBUG_TYPE, "UnsupportedLoopNestDepth",
+                                      OuterLoop->getStartLoc(),
+                                      OuterLoop->getHeader())
+             << "Unsupported depth of loop nest, the supported range is ["
+             << std::to_string(MinLoopNestDepth) << ", "
+             << std::to_string(MaxLoopNestDepth) << "].\n";
+    });
+    return false;
+  }
+  return true;
+}
+
+// Check the metadata for interchange. The outermost one is taken into account
+// and nested ones are ignored. The metadata affects the entire loop nest such
+// that the outermost loop is the loop for which the metadata is specified. For
+// example, in the following example, the loop-interchange will be performed
+// only to the outermost two loops, and the second pragma is ignored.
+//
+// for (...)
+//   for (...)
+//     #pragma clang loop interchange(disable)
+//     for (...)
+//       #pragma clang loop interchange(enable)
+//       for (...)
+//         for (...)
+//           Stmt
+//
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kasuga-fj wrote:

Thanks for your great advice! It's really helpful.

> The idea was instead of having one mighty metadata, to have smaller, composable metadata. Smaller units is what usually an IR is all about,

It makes sense to me, I'm going to try this approach. Please allow me to ask for a review upon completion.

https://github.com/llvm/llvm-project/pull/127474