[PATCH] D123693: Transform illegal intrinsics to V_ILLEGAL

[Matt Arsenault via Phabricator via llvm-commits]

arsenm added inline comments.


================
Comment at: llvm/lib/Target/AMDGPU/SIISelLowering.cpp:8399
+
+  // Add the V_ILLEGAL node to the root chain to prevent its removal.
+  auto Chains = SmallVector<SDValue, 2u>();
----------------
Leonc wrote:
> Leonc wrote:
> > arsenm wrote:
> > > Leonc wrote:
> > > > arsenm wrote:
> > > > > bcahoon wrote:
> > > > > > The v_illegal should have an operand for the chain operand in the original instruction, if one exists.
> > > > > >   
> > > > > > t0 EntryToken
> > > > > > res,ch = intrinsic t0, <other opernads>
> > > > > > ->
> > > > > > res = undef
> > > > > > ch = v_illegal t0
> > > > > > 
> > > > > > Also, if there is a use of the chain definition in the original instruction, then there is no need to add the code below.
> > > > > I'd expect to use the original chain, but it also doesn't really matter given that it's filler anyway
> > > > Thanks @bcahoon & @arsenm.
> > > > 
> > > > I added a check for `MemSDNode` and pass the chain to `V_ILLEGAL` if it exists.
> > > Checking for MemSDNode doesn't make sense, other nodes can have chains. You would need to pass it in from the source if it applies. However I don't think it's worth the complexity, since this really is filler content anyway
> > Thanks, I agree.
> It turns out the chain is necessary. An assertion in `RemoveNodeFromCSEMaps` fails when `Op` is an atomic intrinsic.
Yes, a chain is needed but you should be able to use the entry node. If you want to forward it in from the call sites, that would also be OK


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  https://reviews.llvm.org/D123693/new/

https://reviews.llvm.org/D123693