[llvm] [AggressiveInstCombine] Bail out on graph nodes in unreachable blocks (PR #226383)

[Ömer Sinan Ağacan via llvm-commits]

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@@ -113,6 +113,11 @@ bool TruncInstCombine::buildTruncExpressionGraph() {
     if (!I)
       return false;
 
+    // Instructions in unreachable blocks may be part of a cycle that contains
+    // no phi node, which the reduced expression graph cannot be ordered around.
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osa1 wrote:

What does "ordered around" mean in this context?
How do you order the reduced expression graph around a block?

https://github.com/llvm/llvm-project/pull/226383