[PATCH] D29872: Do not legalize large add with addc/adde, introduce addcarry and do it with uaddo/addcarry

[Amaury SECHET via Phabricator via llvm-commits]

deadalnix added inline comments.


================
Comment at: lib/Target/X86/X86ISelLowering.cpp:23103
+
+  // Let legalize expand this if it isn't a legal type yet.
+  if (!DAG.getTargetLoweringInfo().isTypeLegal(VT))
----------------
zvi wrote:
> deadalnix wrote:
> > zvi wrote:
> > > I know this also appears at the top of LowerADDC_ADDE_SUBC_SUBE, but why it this check needed?
> > Because in that case, the backend wants to run some extra legalization code before coming back there.
> At the time this code runs, there should not be any illegal types present in the DAG. 
> So i am asking why is there a need to check for illegal types?
I'm not sure what the X86 backend is doing, but this is clearly happening looking at the -debug output of llc.


https://reviews.llvm.org/D29872