[v2 of PATCH 06/14] Strip location wrappers in operand_equal_p

[David Malcolm]

On Mon, 2017-12-11 at 18:37 -0500, Jason Merrill wrote:
> On 11/10/2017 04:45 PM, David Malcolm wrote:
> > gcc/c-family/ChangeLog:
> >     * c-warn.c (sizeof_pointer_memaccess_warning): Strip any
> > location
> >     wrappers from src and dest.
> 
> Here the existing calls to tree_strip_nop_conversions ought to
> handle 
> the wrappers.

They don't; when EXP is a VIEW_CONVERT_EXPR wrapper around a VAR_DECL...

11887   static inline bool
11888   tree_nop_conversion (const_tree exp)
11889   {
11890     tree outer_type, inner_type;
11891   
11892     if (!CONVERT_EXPR_P (exp)
11893         && TREE_CODE (exp) != NON_LVALUE_EXPR)
11894       return false;

...tree_nop_conversion bails out at this "return false;", and hence
tree_strip_nop_conversions simply returns the wrapper that was passed
in.

I tried adding fold_for_warn on src and dest, but it doesn't do quite
the right thing, as
  FAIL: c-c++-common/Wsizeof-pointer-memaccess2.c  -std=gnu++98  (test for 
warnings, line 482)
  FAIL: c-c++-common/Wsizeof-pointer-memaccess2.c  -std=gnu++98  (test for 
warnings, line 483)
  FAIL: c-c++-common/Wsizeof-pointer-memaccess2.c  -std=gnu++98  (test for 
warnings, line 484)
...due to "src" changing from being a VAR_DECL to being its STRING_CST
value after the fold_for_warn,

So one approach for Wsizeof-pointer-memaccess*.c is the patch I posted
("[PATCH 06/14] Fix Wsizeof-pointer-memaccess*.c"), which ensures that
any wrappers have been stripped before the call to operand_equal_p in
sizeof_pointer_memaccess_warning.

Alternatively, here's a patch which strips wrappers in operand_equal_p.
FWIW I prefer doing it in sizeof_pointer_memaccess_warning, rather than
touching operand_equal_p.

What do you think?

Successfully bootstrapped&regrtested on x86_64-pc-linux-gnu, as
part of the kit.

gcc/ChangeLog:
        * fold-const.c (operand_equal_p): Strip any location wrappers,
        before computing hashes.
---
 gcc/fold-const.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/gcc/fold-const.c b/gcc/fold-const.c
index 0f11076..2b938900 100644
--- a/gcc/fold-const.c
+++ b/gcc/fold-const.c
@@ -2804,6 +2804,9 @@ combine_comparisons (location_t loc,
 int
 operand_equal_p (const_tree arg0, const_tree arg1, unsigned int flags)
 {
+  STRIP_ANY_LOCATION_WRAPPER (arg0);
+  STRIP_ANY_LOCATION_WRAPPER (arg1);
+
   /* When checking, verify at the outermost operand_equal_p call that
      if operand_equal_p returns non-zero then ARG0 and ARG1 has the same
      hash value.  */
-- 
1.8.5.3