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

[Madhur Amilkanthwar 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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madhur13490 wrote:

Yes, I agree with @kasuga-fj. At this point in the code, we cannot guarantee that the loop nest is legal. For example, if Outer most loop does not have unique exit then transform can terminate. (line [489 ](https://github.com/llvm/llvm-project/blob/d9af03ba80475df5edcab7e4d63004f6115aab3a/llvm/lib/Transforms/Scalar/LoopInterchange.cpp#L489))

(I do plan to pull that check up too, but that is of lower priority.)


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