[PATCH] D86808: [MachineDCE] Delete missed dead instructions after deleting PHI

[Eli Friedman via Phabricator via llvm-commits]

efriedma added a comment.

In general, this pass isn't going to see uses before defs; it's not CFG-sensitive at all.  This isn't specific to PHI nodes.  For virtual registers, maybe we could be doing something like the IR RecursivelyDeleteTriviallyDeadInstructions, to make sure we catch everything?  (Well, everything a simple DCE can catch; ADCE is probably overkill.)

That doesn't really extend to physreg defs, though; we don't currently record the information necessary.  Not sure if we can do anything about that cheaply.



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Comment at: llvm/lib/CodeGen/DeadMachineInstructionElim.cpp:156
+            MachineInstr *FeedMI = MRI->getVRegDef(FeedReg);
+            if (!FeedMI || !isDead(FeedMI))
+              continue;
----------------
You can't use isDead() like this: it queries LivePhysRegs, which is only valid for the current MI.


Repository:
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  https://reviews.llvm.org/D86808/new/

https://reviews.llvm.org/D86808