[PATCH] D69868: Allow "callbr" to return non-void values

[Bill Wendling via Phabricator via llvm-commits]

void marked an inline comment as done.
void added inline comments.


================
Comment at: llvm/lib/CodeGen/MachineVerifier.cpp:701
+      } else if (MBB->succ_size() == LandingPadSuccs.size() ||
+                 MBB->succ_size() == IndirectPadSuccs.size()) {
         // It's possible that the block legitimately ends with a noreturn
----------------
jyknight wrote:
> This isn't correct.
> 
> This line here, is looking at a block which doesn't end in a jump to a successor. So, it's trying to verify that the successor list makes sense in that context.
> 
> The unstated assumption in the code is that the only successors will be landing pads. Instead of actually checking each one, instead it just checks that the count is the number of landing pads, with the assumption that all the successors should be landing pads, and that all the landing pads should be successors.
> 
> The next clause is then checking for the case where there's a fallthrough to the next block. In that case, the successors should've been all the landing pads, and the single fallthrough block.
> 
> Adding similar code to check for the number of callbr targets doesn't really make sense. It's certainly not the case that all callbr targets are targets of all 
> callbr instructions. And even if it was, this still wouldn't be counting things correctly.
> 
> 
> However -- I think i'd expect analyzeBranch to error out (returning true) when confronted by a callbr instruction, because it cannot actually tell what's going on there. If that were the case, nothing in this block should even be invoked. But I guess that's probably not happening, due to the terminator being followed by non-terminators.
> 
> That seems likely to be a problem that needs to be fixed. (And if that is fixed, I think the changes here aren't needed anymore)
> 
> 
Your comment is very confusing. Could you please give an example of where this fails?


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  https://reviews.llvm.org/D69868/new/

https://reviews.llvm.org/D69868