nickdesaulniers marked an inline comment as done.
nickdesaulniers 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]
----------------
jyknight wrote:
> 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.
> 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
Note: child patch D115311 only changes the goto label list for `asm goto`; it
does not change labels in the input list.
> 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.
Ah, I missed that. @void can you clarify; `@bar` looks exactly like `@foo` to
me; was `@bar` copy-pasted from `@foo` without the `blockaddress`es being
updated to refer to `@bar`? I don't really understand the intent of this test;
I don't understand why `llvm-diff` has output for `@bar` but not `@foo`. If
there's a difference, I'm having trouble spotting it.
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D115410/new/
https://reviews.llvm.org/D115410
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