On Thu, Feb 03, 2022 at 03:07:03PM -0500, Jason Merrill wrote:
> > --- gcc/fold-const.h.jj 2022-02-01 20:10:51.235856007 +0100
> > +++ gcc/fold-const.h 2022-02-03 15:02:02.700228631 +0100
> > -/* Non-zero if we are folding constants inside an initializer; zero
> > - otherwise. */
> > +/* Nonzero if we are folding constants inside an initializer or a C++
> > + manifestly-constant-evaluated context; zero otherwise.
> > + Should be used when folding in initializer enables additional
> > + optimizations. */
> > extern int folding_initializer;
> > +/* Nonzer of we are folding C++ manifestly-constant-evaluated context; zero
>
> "Nonzero if"
Oops, thanks for catching it.
> > + if (!folding_cxx_constexpr
> > + && ((DECL_P (base0) && TREE_CODE (base1) == STRING_CST)
> > + || (TREE_CODE (base0) == STRING_CST && DECL_P (base1))
> > + || (TREE_CODE (base0) == STRING_CST
> > + && TREE_CODE (base1) == STRING_CST
> > + && ioff0 >= 0 && ioff1 >= 0
> > + && ioff0 < TREE_STRING_LENGTH (base0)
> > + && ioff1 < TREE_STRING_LENGTH (base1)
> > + /* This is a too conservative test that the STRING_CSTs
> > + will not end up being string-merged. */
> > + && strncmp (TREE_STRING_POINTER (base0) + ioff0,
> > + TREE_STRING_POINTER (base1) + ioff1,
> > + MIN (TREE_STRING_LENGTH (base0) - ioff0,
> > + TREE_STRING_LENGTH (base1) - ioff1)) != 0)))
> > ;
> > - else if (!DECL_P (base0) || !DECL_P (base1))
> > + /* Punt on non-zero offsets from functions. */
> > + else if ((TREE_CODE (base0) == FUNCTION_DECL && ioff0)
> > + || (TREE_CODE (base1) == FUNCTION_DECL && ioff1))
> > + return 2;
> > + else if ((!DECL_P (base0)
> > + && (!folding_cxx_constexpr || TREE_CODE (base0) != STRING_CST))
> > + || (!DECL_P (base1)
> > + && (!folding_cxx_constexpr || TREE_CODE (base1) != STRING_CST)))
>
> I think it would be clearer to leave the !DECL_P case alone and add
>
> /* In C++ it is unspecified, and so non-constant, whether two
> equivalent strings have the same address. */
> else if (folding_cxx_constexpr
> && (TREE_CODE (base0) == STRING_CST
> || TREE_CODE (base1) == STRING_CST)
The point was to let the first if handle for
!folding_cxx_constexpr the cases with STRING_CST
as one or both operands and if that falls through, return 2.
But I guess it could be rewritten as:
if (!DECL_P (base0) && TREE_CODE (base0) != STRING_CST)
return 2;
if (!DECL_P (base1) && TREE_CODE (base1) != STRING_CST)
return 2;
/* Punt on non-zero offsets from functions. */
if ((TREE_CODE (base0) == FUNCTION_DECL && ioff0)
|| (TREE_CODE (base1) == FUNCTION_DECL && ioff1))
return 2;
if (!folding_cxx_constexpr
&& (TREE_CODE (base0) == STRING_CST
|| TREE_CODE (base1) == STRING_CST))
{
if (DECL_P (base0)
|| DECL_P (base1)
|| (TREE_CODE (base0) == TREE_CODE (base1)
&& ioff0 >= 0 && ioff1 >= 0
&& ioff0 < TREE_STRING_LENGTH (base0)
&& ioff1 < TREE_STRING_LENGTH (base1)
/* This is a too conservative test that the STRING_CSTs
will not end up being string-merged. */
&& strncmp (TREE_STRING_POINTER (base0) + ioff0,
TREE_STRING_POINTER (base1) + ioff1,
MIN (TREE_STRING_LENGTH (base0) - ioff0,
TREE_STRING_LENGTH (base1) - ioff1)) != 0))
;
else
return 2;
}
else
...
Jakub
