[PATCH] D109596: [IndVars] Replace PHIs if loop exits on 1st iteration

[Max Kazantsev via Phabricator via llvm-commits]

mkazantsev added inline comments.


================
Comment at: llvm/lib/Transforms/Scalar/IndVarSimplify.cpp:1317
+  for (auto &PN : LoopHeader->phis()) {
+    auto *PreheaderIncoming = PN.getIncomingValueForBlock(LoopPreheader);
+    PN.replaceAllUsesWith(PreheaderIncoming);
----------------
reames wrote:
> As written, this code does not preserve LCSSA.  Consider the case where we have two sibling loops and the header of the second is directly an exit block of the first.  This is not loop simplify form (i.e. no preheader), but it is a possible case.  
Philip, there is an assert on line 1741 that the loop is in simplify form. I don't think the situation you are referring to is even possible.


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  https://reviews.llvm.org/D109596/new/

https://reviews.llvm.org/D109596