jyknight added inline comments.
================
Comment at: llvm/test/tools/llvm-diff/callbr.ll:28-29
entry:
- callbr void asm sideeffect "", "X,X,~{dirflag},~{fpsr},~{flags}"(i8*
blockaddress(@foo, %t_no), i8* blockaddress(@foo, %return))
+ callbr void asm sideeffect "", "i,i,~{dirflag},~{fpsr},~{flags}"(i8*
blockaddress(@foo, %t_no), i8* blockaddress(@foo, %return))
to label %asm.fallthrough [label %return, label %t_no]
----------------
nickdesaulniers wrote:
> pengfei wrote:
> > jyknight wrote:
> > > pengfei wrote:
> > > > If my above assumption is true, I think we can't replace the `X` with
> > > > `i` here.
> > > > Besides, I'm confused on the indirect labels list. Are they the labels
> > > > of `bar` or `foo`?
> > > I don't see a a problem with using "i" everywhere -- all blockaddress are
> > > going to be immediate values no matter whether they're an indirect target
> > > or not.
> > >
> > > The indirect labels list is only referring to labels in the current
> > > function.
> > >
> > > This test is confusing, but, it is a test for llvm-diff, so that's okay
> > > or maybe even intended. (It can't actually possibly jump to @bar:%return
> > > or @bar:%t_no, because nothing ever gets the address of those labels. It
> > > does get the similarly-named labels in @foo, but it can't jump to those
> > > either, since they're in a different function.)
> > Thanks for the explanation. My point is the test3 above intended to use `X`
> > to indicate the destination is not in the indirect labels list. For
> > consistency, we should use `X` here too, since the @foo:%return etc. are
> > not in the list either. Or we don't need to use `X` in test3.
> The "indirect destination list" for the `callbr` in `@bar` is the `[label
> %return, label %t_no]`. Both operands have corresponding `blockaddress`
> arguments. So they //should not// use `X` in this case.
I don't see why the correct constraint to use should be related at all to
whether the blockaddress argument corresponds to a label in the indirect label
list or not.
Using something other than "X" should probably always be preferred, since
presumably the instruction you're emitting has requirements. (Unless of course
you don't actually use the argument, or only use it in a comment, or something
like that...in which case "X" is fine.)
But, FTR, in this test, the blockaddress is for a label in a //different//
function ("@foo") than the function we're in ("@bar"), which is what pengfei
was pointing out.
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D115410/new/
https://reviews.llvm.org/D115410
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