[PATCH] D56571: [RFC prototype] Implementation of asm-goto support in LLVM

[Jennifer Yu via Phabricator via cfe-commits]

jyu2 marked 2 inline comments as done.
jyu2 added inline comments.


================
Comment at: lib/Sema/SemaStmtAsm.cpp:470
+    if (NS->isGCCAsmGoto() &&
+        Exprs[ConstraintIdx]->getStmtClass() == Stmt::AddrLabelExprClass)
+      break;
----------------
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;
}




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https://reviews.llvm.org/D56571