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

[Sjoerd Meijer 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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sjoerdmeijer wrote:

I was wondering if the state that we are trying to capture here (interchange is legal, but unknown if profitable) is caught by the "Loops are legal to interchange" debug message so that we can change that in an optimisation remark and don't need this new one.

Alternatively, I don't mind changing this optimisation remark in a debug message. In general I don't like tests that rely on debug builds, but this is an exception that would be okay I think. 

But I don't have strong opinions on this to be honest, so WDYIT @madhur13490 ?

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