efriedma added inline comments.
================
Comment at: lib/Sema/SemaStmtAsm.cpp:470
+ if (NS->isGCCAsmGoto() &&
+ Exprs[ConstraintIdx]->getStmtClass() == Stmt::AddrLabelExprClass)
+ break;
----------------
jyu2 wrote:
> jyu2 wrote:
> > efriedma wrote:
> > > jyu2 wrote:
> > > > efriedma wrote:
> > > > > jyu2 wrote:
> > > > > > efriedma wrote:
> > > > > > > This looks suspicious; an AddrLabelExpr could be an input or
> > > > > > > output, e.g. `"r"(&&foo)`.
> > > > > > Syntax for asm goto:
> > > > > > Syntax:
> > > > > > asm [volatile] goto ( AssemblerTemplate
> > > > > > :
> > > > > > : InputOperands
> > > > > > : Clobbers
> > > > > > : GotoLabels)
> > > > > >
> > > > > > Only input is allowed. Output is not allowed
> > > > > >
> > > > > That doesn't really address my point here... ignore the "or output"
> > > > > part of the comment.
> > > > Sorry did not realize that. Thank you so much for catching that. Need
> > > > to add other condition "ConstraintIdx > NS->getNumInputs() - 1", change
> > > > to :
> > > >
> > > > if (NS->isGCCAsmGoto() && ConstraintIdx > NS->getNumInputs() - 1 &&
> > > > Exprs[ConstraintIdx]->getStmtClass() ==
> > > > Stmt::AddrLabelExprClass)
> > > > break;
> > > >
> > > > Is this ok with you? Thanks
> > > That's the right idea. But I still see a few issues at that point:
> > >
> > > 1. The AddrLabelExprClass check is redundant.
> > > 2. "NS->getNumInputs() - 1" can overflow; probably should use
> > > "ConstraintIdx >= NS->getNumInputs()".
> > > 3. "break" exits the loop completely (so it skips validating all
> > > constraints written after the label).
> > > 4. The code needs to verify that the user correctly specified the "l"
> > > constraint modifier.
> > Sorry not done yet.
> For you comment 4:
>
> The code needs to verify that the user correctly specified the "l" constraint
> modifier. We already emit error like following?
>
> Do you mean, we need more checking here? Thanks.
>
> n.c:4:35: error: unknown symbolic operand name in inline assembly string
> asm goto ("frob %%r5, %1; jc %l[error]; mov (%2), %%r5"
> ~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~
> n.c:8:15: error: use of undeclared label 'error1'
> : error1);
>
> Test is:
> int frob(int x)
> {
> int y;
> asm goto ("frob %%r5, %1; jc %l[error]; mov (%2), %%r5"
> : /* No outputs. */
> : "r"(x), "r"(&y)
> : "memory"
> : error1);
> return y;
> error:
> return -1;
> }
>
>
I mean, there needs to be a diagnostic for the following:
```
asm goto ("jne %h0"::::x);
```
On a related note, there should also be a diagnostic for the following
somewhere:
```
asm ("jne %l0"::"r"(0));
```
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D56571/new/
https://reviews.llvm.org/D56571
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