[llvm] [LoopInterchange] Hoist isComputableLoopNest() in the control flow (PR #124247)

[Ryotaro Kasuga via llvm-commits]

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@@ -1761,10 +1759,23 @@ PreservedAnalyses LoopInterchangePass::run(LoopNest &LN,
   // Ensure minimum depth of the loop nest to do the interchange.
   if (!hasSupportedLoopDepth(LoopList, ORE))
     return PreservedAnalyses::all();
+  // Ensure computable loop nest.
+  if (!isComputableLoopNest(&AR.SE, LoopList)) {
+    LLVM_DEBUG(dbgs() << "Not valid loop candidate for interchange\n");
+    return PreservedAnalyses::all();
+  }
+
+  ORE.emit([&]() {
+    return OptimizationRemarkAnalysis(DEBUG_TYPE, "Dependence",
+                                      LN.getOutermostLoop().getStartLoc(),
+                                      LN.getOutermostLoop().getHeader())
+           << "Computed dependence info, invoking the transform.";
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kasuga-fj wrote:

As discussed above, I think this message is just for testing that the process exits **before** computing dependence info if the loop is not computable. To achieve this, inserting a new message here seems to be reasonable to me.
However, in terms of messages to users, I think this is a bit excessive or noisy. Replacing it with `dbgs()` would be one option. It depends on which what we want to prioritize: test coverage or having useful "technical" messages for users.

https://github.com/llvm/llvm-project/pull/124247